Throughout the barred owl's range, other birds are taken as prey, although avian species make up a much smaller proportion of their diets than mammals. The maximum known representation of bird prey in a barred owl food study was 25.1% in Alberta, meaning that they augment their diet less heavily with bird prey than their near equivalent in Europe, the tawny owl. No specific variety of bird is subject to the most frequent predation by barred owls and birds are the most diverse class in these owl's prey spectrum, with more than 100 species of bird known to be hunted.  Conspicuous nesting sites of barn swallow and purple martin on manmade structures and objects were revealed via video-monitoring to suffer heavy predation by barred owls. In the case of the barn swallows, all ages of swallow as well as possibly eggs were eaten. 65 of 95 monitoring barn swallow nests were consumed by owls over a 3-year period. The muddy bank nests of cliff swallows are also vulnerable to barred owls, while other swallow species are known to be opportunistically taken.
In more enclosed wooded areas, radio-tagging and video-monitoring of various passerines nests as well as examinations of owl pellets has shed light on the relationship of barred owls with these potential prey resources. Not only was the barred owl found to be a surprisingly routine predator at woodland passerine nests, but that an unexpected bulk of the acts of predation in studies from Missouri and Illinois were carried out during the daytime. Many different forest bird species (most frequently acadian flycatchers and indigo buntings in Missouri and Illinois) were hunted. These studies indicated that the barred owl may snatch passerines of any age, but recent fledglings are taken preferentially due to their more conspicuous behavior and limited ability to fly away. In Minnesota, about 62% of studied hermit thrush and ovenbird fledglings were taken per one study, with all thrush that nested in the 50 m (160 ft) radius of the barred owl's nests failing to produce any young. A similarly high rate of local determent by barred owls has been found for other woodland thrushes like the veery, wood thrush and varied thrush, with the additional finding that pre-dawn singing by certain thrushes, when their escape abilities are dulled by the dim light, leaves them vulnerable to barred owl ambushes. Forest birds seem to recognize the barred owl as a threat, with mobbing behavior evoked easily by playing recordings of their calls in the daytime.
A wide diversity of bird prey may be occasionally hunted by barred owls in different circumstances. Smaller or mid-sized bird prey species known have including different species, though usually a relatively low species diversity and in low numbers, beyond swallows and thrushes of tyrant flycatchers, vireos, chickadees, wrens, mimids, tanagers, other cardinalids and finches. Somewhat higher diversity of species are known from the sparrow and warbler families. Birds down to the size of the calliope hummingbird, North America's smallest hummingbird at 2.7 g (0.095 oz), may be taken by barred owls. At the opposite end of passerine prey for barred owls, this species will sometimes take all ages of the American crow, from very young nestlings to adults. Numerous non-passerine birds are also taken, though seldom in great numbers and of low known species diversity. One exceptional family is the woodpeckers, which are probably so widely taken because of their generally overlapping habitat preferences with those of barred owls. Several species of woodpecker are preyed upon almost throughout the range, including at least a half dozen in Oregon alone, from the smallest North American species, the downy woodpecker, to the largest, the pileated woodpecker. Other small-to-medium-sized bird species known as prey for barred owls are: mountain quail, grey partridge, rock dove, band-tailed pigeon, mourning dove, purple gallinule, killdeer, American woodcock, least tern, snowy egret, cattle egret and belted kingfisher. Although they take many chicks of gamebirds, adults of these species are vulnerable as well. In many areas, ruffed grouse are not infrequently taken, comprising up to nearly 6% of prey items in Alberta. In Oregon, the weights estimated for ruffed grouse taken by barred owls varied enormously, from small chicks estimated at 25 g (0.88 oz), to adults weighing about 576 g (1.270 lb). Broader study in the Pacific Northwest indicated that adult ruffed grouse were mainly taken. Barred owls are also known to take adult spruce grouse of about the same size as the ruffed grouse, as well as much larger species including the common pheasant and the sooty grouse, the latter estimated to average 1,050 g (2.31 lb) when taken. Barred owls are also known to prey on the young of other, larger birds, such as the American white ibis and wild turkey.


Barred owl predation on reptiles is widely reported but they seldom take large numbers in any given area. Most reported instances of such captures are of various small lizards, often of skinks in the genus Plestiodon, most often from the Midwest to the western parts of the range. Several reported instances of barred owls hunting snakes are also known, but they are perhaps even more seldom preyed upon than lizards. More than a half dozen snake species are known to be captured, several of which are colubrids, which are mostly harmless. The estimated body mass of black racer taken in Oregon was only 77 g (2.7 oz), well under their mean mature size. However, consumption or predation on dangerous pit vipers, such as timber rattlesnakes and copperheads, by barred owls has been reported, although it is not known whether these are taken as adults. Rarer still is barred owl predation on turtles. Predation by this species was reported upon a very young river cooter, which had a carapace width of only 31.4 mm (1.24 in), as well as on juvenile gopher tortoise and apparently diamondback terrapin. Much more characteristic than any reptilian prey are amphibians, with various types of frogs, salamanders and similar species reported in this owl's foods. Amphibians were more considerably more popular in the diet in western part of range, comprising 10.5% of known studies against 4.4% in the east. In total, well over 20 amphibian species have been identified in the foods of barred owls and amphibians collectively can make up to 24.5% of the local diet (as was reported in Alberta). While salamanders and newts are probably often visually discerned while scanning the forest floor, many frogs are probably hunted down by sound during their crepuscular choruses.
Amphibians are taken almost entirely during the breeding season, as they become unavailable to barred owls during the winter months. Most reported amphibian prey in Oregon were unidentified "medium-sized salamanders". A diversity of frog sizes may be taken, varying potentially in size from spring peepers, which average around 4 g (0.14 oz), to American bullfrogs, which average around in mature bullfrogs 430 g (15 oz). A notable act of successful predation was carried out by a barred owl on a rough-skinned newt, which contains toxins that are often deadly to predators. Apparently, the owl was able to survive after consuming the newt. The rarest variety of vertebrate prey for barred owls is fish. However, there are several accrued accounts of fishing by these owls, including older accounts of barred owls coming to ice holes made by human fishermen and more recent accounts of possibly routine fishing by the owls on the St. Johns River in Florida, in the latter case utilizing a fishing dock as a hunting perch. At least five species of fish have been identified in the foods of barred owls, including fairly large fish like brown bullheads and largemouth bass.
The balance of assorted invertebrates in the diet of barred owls can be quite high. Although many of those found in pellets are unidentified to species, nearly 40 species of invertebrates have been found in their foods. Broad studies indicate arthropods (including millipedes and spiders but predominantly insects) in general comprise up to about 16% of the barred owl's foods. When hunting insects, barred owls most often prefer ground-based beetles. In Oregon, 11.7% of the diet was assorted beetles (14 species were identified), being somewhat more numerous among 3686 prey items than other non-rodent prey orders. However, some insects prey such as luna moth, eastern tiger swallowtail and green darner are presumably hawked on the wing around dawn and dusk. It is known that barred owls will sometimes come hunt near manmade light sources and campfires, flying out from the perch to quickly capture flying insects that were attracted to them. Of 123 prey items found in southern Manitoba, flying Sphinx moths and flightless scarab beetles each comprised 7% (most of the remaining balance being unidentified mammals and birds). Crayfish of at least four identified species are another widely taken type of invertebrate, presumably snatched up by barred owls from shallow waterways. Crayfish seem to be exclusively taken in the east and Midwest, areas where they comprised 3.4% of all known food studies, and none at all were recorded in the western part of the range. In Missouri, annually up to 31.1% (though, in some years, 0%) of the diet was comprised by crayfish. Barred owls occasionally feed on snails and slugs, the latter especially in the Pacific Northwest. Another snail, the Pacific sideband, was surprisingly often present in the foods in Oregon as at least 135 were taken. Beyond slugs, other "soft" invertebrates are sometimes hunted, especially earthworms. Earthworms were most prominent in the foods of barred owls in Nova Scotia, where 27.6% of 186 video-monitored prey deliveries in Nova Scotia were worms, the most regularly delivered of all prey types there.


The barred owl's range overlaps with multiple other predators of similar prey species. Due to the time period barred owls are active, the most interaction occurs with other owl species. Of the owls in North America, about three-quarters are reliant on similar small mammal prey, usually rodents, with a mixture of other prey genera as supplements. Other than its ecology where it today co-exists with spotted owls, however, there is some level of niche differentiation from a majority of sympatric owls. In the eastern forest biome, the barred owl is the only large owl species to dwell mainly in continuous forest areas. While many of the owls sympatric with barred owls over majority of their eastern and Midwestern range share a preference for hole-nesting, smaller hole-nesting owls usually prefer different habitats, such as the open country-dwelling barn owl and the screech owls, which usually in North America dwell at the interface of forest and open habitats. Both North American species in the Aegolius owl genus are forest-dwelling cavity nesters but are much smaller and are at entirely different trophic levels.
A singular diurnal raptor species that mirrors the barred owl at nearly all ecological levels is the red-shouldered hawk. Both species have similar distributions, habitat preferences and somewhat similar dietary habits and trophic level. They may considered as nearly nocturnal and diurnal ecological equivalents. In multiple parts of the range, including southwestern Ohio, North Carolina and northern Michigan, the paralleling habitat usage and nesting behavior of the barred owl and red-shouldered hawk has been noted. One of the few respects in which their habitat usage differs is that the barred owl is more adaptive to nesting in suburban areas if they have old growth trees that provide plentiful tree hollows. In contrast, red-shouldered hawks tend to avoid suburban areas whilst nesting, but may acclimate to these areas during the winter. Barred owls seldom alter their range throughout the year and remain more or less constrained to the stands they used during nesting. The red-shouldered hawk averages somewhat smaller and has a more limited diet than barred owls, but probably goes after dangerous prey such as snakes more regularly. Multiple occasions are recorded where the barred owl and red-shouldered hawk have nested in the same area, often within the same grove of trees, remarkably with little to no conflict. At least one nest was found including eggs from both species. When nesting near other hawks like red-tailed hawks and Cooper's hawks, the relationship tends to be much more contentious between hawk and owl, despite barred owls sometimes sharing space or using the old nests of these hawks. A wing-clapping display by a pair of barred owls was recorded during antagonistic encounters in Manitoba with a pair of broad-winged hawks. Wing-claps were previously not recorded in this species, and when recorded for other owl species were often for the purposes of courtship displays.
One predator that is a major source of conflict for the barred owl is the great horned owl. In every part of their range, barred owls are compelled to share space with the larger owls. There is habitat partitioning between the barred owl and great horned owl that allows them to often co-exist. Great horned owls prefer various more open habitats mixed with trees, often in rather upland areas, which differs from the habitats preferred by the barred owl. If a great horned owl moves into an area, barred owls appear to avoid said areas, based on radio telemetry data. In much of the east, habitat alteration and fragmentation tends to favor the great horned owl at the expense of the barred owl. Where more continuous forest is available, however, the great horned and barred owl can occur surprisingly close to one another. In one case, a barred owl was observed to roost only 400 m (1,300 ft) from a great horned owl. In general the reforestation at the northern sections of the Great Plains have, on the contrary, benefited barred owls (and may have been a part of allowing their westward expansion) and been perhaps slightly detrimental to the great horned owl. However, even where the habitat becomes less ideal, the great horned owl is unlikely to vacate an area, unlike the barred owl which can be entirely displaced if woods become too small and fragmented. Great horned owls and barred owls have similar diets, as both are wide-ranging, large and opportunistic owls. However, the great horned owl is larger in bulk, sometimes averaging nearly twice as heavy, with much heavier, larger feet and talons. The great horned owl is probably rather more powerful and accesses a wider variety of prey than barred owls, which additionally take considerably fewer prey species because they occur in more limited habitats and have a much smaller overall distribution. A study utilizing stable isotopes in Alberta appeared to confirm that the great horned owl preys on nearly twice as many prey species as do the barred owls of the area.
The great horned owl is indeed likely to be the greatest natural enemy of the barred owl. There are several accounts of the horned owl species preying on nestlings, fledglings and adults of the barred. Other than horned owls, predation of the barred owl seems to be fairly rare outside of the nestling age, both due to the owl's relatively large size and their nesting habits, most often in secluded tree hollows. One more virulent nest predator is likely to be raccoons (Procyon lotor), which can nearly decimate both tree hollow and stick nest locations of almost any kind of bird, especially in peri-urban areas where they largely exist without controlling predators. Both the American marten and the fisher are known to be nest predators of barred owls, in turn appearing to cause the owls to switch nest sites. Other birds of prey may be an occasional threat to barred owls. Northern goshawks have reportedly killed both young and adult barred owls. One modern account mentions predation by a goshawk on a nestling barred owl (i.e. weight about 392 g (13.8 oz)). A well-known instance of a goshawk attack on an adult barred owl concluded with the owl and goshawk killing one another. There are some very rare, singular cases of predation on barred owls (age unknown) by red-tailed hawks, which nonetheless generally appears to be a less menacing co-inhabitant than the goshawk. More surprisingly, a Cooper's hawk, a smaller species of raptor, was observed to apparently prey upon a full-grown barred owl in British Columbia. An American alligator was reported to have preyed on a barred owl in at least one instance.
On the other hand, the barred owl is a significant predator of smaller raptor species as well. Most smaller owls that co-exist with barred owls are at occasional risk of predation. A particular cause of concern in intraguild predations by the barred has been their encroachment into the areas inhabited by western screech owl (Megascops kennicotti). Several instances of predation have been noted on the screech owls and the recent, unprecedented presence of the barred owls appears to have a correlation with the decline of the western screech owl in British Columbia and in Bainbridge Island, Washington. In one instance, a biologist who called in an eastern screech owl (Megascops asio) in Ohio observed it to be immediately captured and consumed by a barred owl. The barred owl is a serious predator of eastern screech owls, but is less deadly to them in general than the great horned owl. Various additional owl species known to be preyed upon by barred owls including the flammulated owl (Psiloscops flammeolus), northern pygmy owl (Glaucidium gnoma), northern saw-whet owl (Aegolius acadius) and long-eared owl (Asio otus). The interspecific owl trophic chain was perhaps most conspicuous in a case where a barred owl that was shot in New England was found to have a long-eared owl inside its stomach which in turn had an eastern screech-owl in its own stomach. More unexpectedly, barred owls may even prey on other Strix species. As many as four records of circumstantial but likely predation by barred owls on spotted owls have been reported. A likely event of predation by a barred owl on an adult great grey owl was observed. The authors hypothesized that the victim may have been a smaller male great grey owl (which can be about the same body mass as a large female barred) but this is the only known instance to date of a great gray owl being killed by another species of Strix owl. Barred owls have been known to take adults (or full-grown juveniles) of diurnal raptors as well, including snail kites, Cooper's hawks, sharp-shinned hawks and possibly swallow-tailed kites.


The barred owl's usual preferred a nest site is usually the hollow trunk of a large tree or the broken-off snag from a large tree branch. Hollows or snags may be made by any variety of sources, often due to a disease or storm, with hollows and snags large enough to accommodate these birds usually only occurring in an old-growth tree. Typically, nest sites are in rather deep and dark wooded areas, often with a well-developed understory but somewhat sparse lower branches, and may be fairly close to water. Average nest heights are between 6.8 and 13.4 m (22 and 44 ft) above the ground.  In 25 studies from throughout the range, mean nest tree height was 18.2 m (60 ft) (lowest mean from Florida where it was 5.9 m (19 ft); the highest from Oregon where it was 28 m (92 ft)), mean nest tree diameter was 65.7 cm (25.9 in) (thinnest mean in Saskatchewan at 47.4 cm (18.7 in); thickest in Washington at 106 cm (42 in)), while the mean height of the tree cavity used from these studies was 9.8 m (32 ft).
A big beech with a rotting core, encompassing a large cavity reached through a deep crevice, is an ideal nest site. The most widely reported nesting trees in breeding cards were elms (21%) and beeches (15%), followed by oaks, hickories, yellow birches, sycamores, aspens, maples and poplars. In Washington, the most often used nest trees were balsam poplar, Douglas fir and grand fir. Balsam poplar comprised 62% of known nest sites in Manitoba as well. It was found in Maryland that snags used were significantly higher than the average height of miscellaneous snags available in environment. The mean size of tree holes the owls used in Maryland was 33 cm (13 in) in inside diameter and 54 cm (21 in) in depth. These were slightly larger than the average from Michigan, which hollow used averaged 25 cm (9.8 in) in mean diameter and 35 cm (14 in) in mean depth. Record depth tree cavities used by barred owls was around 2.4 m (7.9 ft) deep from the opening on the tree. One study of cavity nesting birds in Ontario found that the barred owl preferred to nest in the most massive trees of any cavity-nester in the study area. In continuous bottomland forest, nests are often about every 226 ha (560 acres). Territory lines often remain the same even after the original owls are replaced entirely by a new pair. It was thought in Nova Scotia that some pairs may prospect a potential nest site as much as year before they use it. Despite usually using sickly or dying trees, some nests have found in partially hollow but still living oaks.
Usually in areas with few or no natural tree hollows, often within younger secondary forests or overharvested areas, this species will uses other birds’ nests and occasionally also the dreys of squirrels. Evidence shows that the preference of barred owls for hollows and snags over bird nests is due to their earlier nest type having a more secure microclimate with better shelter (additionally, owl nests in hollows generally tend to be somewhat less vulnerable to predation than those of owls using old bird nests). Nest built by other birds that are most widely used are probably red-shouldered hawk and Cooper's hawks, while those of red-tailed hawks, usually being in more open areas, are used secondarily outside of a local basis. In the south, nests have been found between fronds of palmetto palm leaves, in holes of broken palm stems and rotten snags of the palms. One unconventional nest was on the ground at the base of a lookout tower in Everglades National Park. Another was on the roof of a shed in Saskatchewan. Yet another was in an earthen bank in Texas. Locally, barred owls can take to nest boxes but, in general, barred owls take to these less readily than their cousin Strix owls in Europe. Suitable nesting hollows may be used quite often in subsequent years, with records of a single hollow seeing up to 25 years of barred owl use (presumably not by the same owls however). Other long-used nests were one reused in New England for 10 years by the same pair until it rotted out and while a nest box in Nova Scotia was reused 10 times over 16 years. Over 6 years in Minnesota, 14 nest boxes were reused; 7 were used once, 6 were twice and one was used three times. Like all owls, barred owls never construct their owl nest but they may press or dig slightly if soil is present or remove the top leaves from a squirrel drey.
In normal circumstances, barred owls tend to pair bond for life. Courting pairs are usually newly mature birds but also possibly widowed owls or those re-establishing existing pair bonds after the winter. During courtship, barred owl males especially may engage in nodding, bowing with half-spread wings and may wobble and twist their head from side to side. Copulation between pairs usually occurs in late winter, February to March, and occurs several times, probably to ensure implantation. The female enters a pre-breeding lethargy stage wherein she is fed by the male. In barred owls, egg laying occurs at two to three day intervals.  Egg laying typically begins in March and runs throughout April. In more tropical locales like Florida, egg laying may occur as early as late December, though 22 were laid in between early January and early March. At similar latitudes in Texas, 22 first eggs were laid between as early as mid-February to as late as early June (although the latter may have been a replacement clutch). 23 clutches in Iowa and Illinois were initiated in between late February and late April, with roughly corresponding initial egg dates in New Jersey and probably western Maryland as well. 63 initial eggs in New England were laid between mid-March and mid-May. Further north, 38 clutches in Nova Scotia were initiated in between late March and late May, with initial clutches dates about a week later in Ontario. Normally the female lays 2 to 3 eggs, although as many as 5 is possible, directly on the base of the nest site. The mean clutch size in three broad samples from several parts of the range was between 2.22 and 2.46. In Minnesota, the mean clutch size was 2.68. The eggs are pure white, slightly rough and not glossy, and oval in shape. In 157 eggs, the length of the egg could measure from 42.5 to 55.5 mm (1.67 to 2.19 in) while the diameter could range from 37.5 to 45.3 mm (1.48 to 1.78 in), with a mean of 50.6 mm × 43.3 mm (1.99 in × 1.70 in). 25 eggs in Nova Scotia averaged slightly smaller, at 49 mm × 41 mm (1.9 in × 1.6 in). The mean weight of the egg is around 45.5 g (1.60 oz). The female alone incubates, doing so for about 28 days, while the male gathers food for her.
The female tends to closely brood the young for three weeks. Then after, she begins to hunt for the young. Both parents normally continue hunt for the young until they are about 6 weeks old and can fly well. During the first three weeks, the male does all prey deliveries, either bringing prey directly into the nest or leaves for the female at the nest entrance or on a nearby branch. The mean number of prey deliveries when the young are 6–10 days old is 2.4 per night, 1.4 when they are 11–15 days old, 3.6 when they are 16–20 days old and 2.2 when they are 21–25 days old. He will continue hunting until the young disperse. The female's prey deliveries are much more frequent when she resumes hunting, ranging from a mean of 4.8 to 8 deliveries nightly. Male prey deliveries are often sporadically at any point through the night while female deliveries tend to be clustered immediately after sunset or just before sunrise. Barred owls have a variable reaction to human disturbance. Some parent owls remain sitting, while some leave the nest upon a person's approach and some attack people climbing to the nest, as well as those approaching young on or near the ground. There are several accounts of barred owls engaging in fierce nest defense against humans, sometimes reportedly knocking people out of trees. However, their aggression is variable and, based on studies of similar owls like tawny and Ural owls from Europe, attacks tend to only occur when intrusions and disturbance by humans are frequent. A distraction display was recorded by a female barred owl when humans approached. In it, she spread and quivered her wings and engaged in chittering and squealing, somewhat similar to the sounds made by begging young.
The average hatchling weighs about 46 g (1.6 oz). Like most birds, the young are initially altricial. The white down feathers that the barred owls are hatched with is replaced by white-tipped barred-buff second down at two to three weeks of age, correspondingly with growth of the wing primaries. The earlier chicks are bigger and stronger, while the latter ones may not survive if food is scarce. Size differences between barred owl nestlings may be less pronounced if the female does not begin incubation until the laying of the second egg. The larger young may fight with the younger siblings for food. The young barred owls first start moving about the nest at around this 3 week point and may start to perform threat displays if scared. Adult-like feathers begin to appear at six weeks of age, starting at the scapulars, then radiating down across the abdomen and flanks up through the upper breast, with the last wisps of down remaining for up to 4 months. The young often start exploring around the nest tree, often falling to ground, which makes them quite vulnerable to predation despite the parents' continued protection. However, the fledglings can usually clamber back up the tree using their feet and bills, constantly wing-flapping.
Fledging occurs at about 36–39 days. After that, both parents continue to hunt for the young but prey deliveries taper off as the young begin to make their first flights and practice hunting. Short flights are typical when the young barred owls are up to around 10 weeks old with longer flights commencing at about 14 weeks. By the time they are flying and hunting somewhat assuredly in early to mid-autumn, the young move away and gain independence. Dispersal of 5 young from Nova Scotia was 0.8 to 64 km (0.50 to 39.77 mi) away from their nests of origin. Furthermore, a recovered 6 month old was 8 km (5.0 mi) away from its nest of origin, while five encountered as adults were found at a distance of 16 and 43 km (9.9 and 26.7 mi) from the nests where they hatched. An exceptional dispersal distance from Nova Scotia was 1,600 km (990 mi) away to Stoney Creek, Ontario. The post-dispersal stage is one of great mortality among young owls. Usually juvenile owls are considered "floaters", often hovering around the perimeter of fiercely defended territories for some time. In some areas, floaters may make use of nest boxes more readily than mature birds. Yearlings have been known to breed only very rarely, otherwise barred owl usually first breed when they are around two (sometimes three) years old. Therefore, around two years old is considered the age of maturity. The percentages of successful nests (i.e. at least 1 fledgling produced per attempt), per study were found to be: 86% of 22 clutches in Minnesota (with a mean of 2.42 fledglings per successful attempt), 66% of 114 clutches in Michigan (with a mean of 1.97 fledglings per successful attempt), 25% of 6 clutches in Maryland (with a mean of 1 fledgling per all attempts and 1.48 per successful attempts), 69% of 48 clutches in Nova Scotia (with a mean of 0.25 fledgling per all attempts and 2 per successful attempts) and 50% of 12 nests in Washington state. Little is known about the specific factors that dictate breeding success, but are likely to include the quality of the nesting site, the food supply in the area, the levels of disturbance from outside actors (usually humans) and the maturity of the pair.


The barred owl is a naturally long-living bird. Some record lifespans recorded per banding studies in the wild are 18 years 2 months (initial banding Kentucky, died in Ohio) and 24 years and 1 month in Minnesota. There are several records of breeding barred owls nesting successfully for a decade or more. The record lifespan for a barred owl in captivity, where many animals can live longer without the stresses of surviving in wild conditions, was 34 years and 1 month, with six records of captive barred owls living over 30 years. Known causes of mortality are diverse, some due to predation (largely great horned owls, for nestlings to adults, and probably raccoons, for eggs, nestlings and fledglings). Some mortality is known to occur during hunting accidents. There are cases of barred owls being inadvertently killed in furbearer traps. Sometimes deaths occurs due to the defenses of prey. One barred owl was killed by the bite of an unknown rodent that was likely defending itself. Some cases of cannibalism between adult barred owls have been reported as well. This species, like other forest owls, is vulnerable to the respiratory disease aspergillosis. Spontaneous infections of West Nile fever are also known to kill wild barred owls. Barred owls were the most regularly infected with West Nile Virus of owl species in Georgia, as about 15% of studied barred tested positive (still at a lower rate than some hawks). Cases of Avipoxvirus are also known in barred owls but, as with West Nile virus, the rate of mortality to viral infection is not well-known. A case of follicular thyroid cancer was found in a wild barred owl that was unable to continue to fly. Fatty liver diseases have been recorded for barred owls in captivity. Eye lesions are fairly common in barred owls, but can be survived and possibly surgically corrected.
Parasitism is frequent in barred owls as expected for many different kinds of wild birds. The parasite load was determined to be higher in larger owls in Florida like the barred and great horned owl and lower in smaller owl species, like eastern screech owl. While parasitic infestations are not typically detected as direct mortality causes, in some severe cases complications or direct death can occur. These cases of mortality are most widely recorded in cases of Toxoplasmosis, although generally owls have lower rates of this dangerous parasite than some other species of birds of prey. Of barred owls in one study, 26.7% had Toxoplasma gondii, the cause of Toxoplasmosis, upon necropsy study, with adults having it more often than immature birds. Lethal cases of Trichomoniasis are also known. The effect of other parasites are more poorly known beyond generally compromising their condition but in one case Sarcocystis may have caused paralysis in one barred owl. Other parasites recorded in barred owls include Eimeria varia, Novyella, Neodiplostomum as well as apparently rare species of Centrorhynchus and Tetrameres that were first found within barred owls. Trematode flatworms such as strigeids as well as Tylodelphys and Brachylaima are found in intermediate volume in barred owls relative to other owls. Invertebrates such as hippoboscid flies and Mallophaga are known to infect barred owls as ectoparasites but seldom at severe levels. Concern was expressed that barred owls may compromise spotted owl populations with novel parasites. However, studies of Haemoproteus in barred and spotted owls in northwestern California found that native parasites were finding a new host in barred owls and may have been transmitted from spotted to barred owls but that the barred owl acted as a poor parasite host and may have diluted the parasite levels in owl populations. Furthermore, there was no evidence found that barred owls were spreading parasites to spotted owls.


The barred owl is one of the most common owls in North America. Partners in Flight estimates that the barred owl may number up to 3 million individuals globally, making it the perhaps the second most numerous North American owl behind the great horned owl and perhaps slightly ahead of other commoner species like barn owls and northern saw-whet owls. It estimated that Canada in total holds about 10,000-50,000 pairs. Canadian Maritimes had highest densities known, with 3600 pairs, being found in 80% of 10 km² (3.9 sq mi) blocks totaling 377; this was a conspicuously higher density than that recorded in Ontario, where they were in 28% of 1824 study blocks. Iowa, Tennessee and Maryland had the highest densities of pairs apparently in the United States, being present from 39 to 47% of blocks. Throughout the year, the mean number of sightings per route is 0.12 sightings while during Christmas Bird Counts (CBC), the mean in 0.25 per route.


Barred owls are thought to be partly responsible for the recent decline of the northern spotted owl, native to British Columbia, Washington, Oregon, and California. The 2011 Revised Recovery Plan for the Northern Spotted Owl (p. vi) states "Based on the best available scientific information, competition from the barred owl (S. varia) poses a significant and complex threat to the spotted owl." Northern spotted owls were thought to be already declining considerably before barred owls moved into their range, mostly in sync with large-scale logging operations and land development carried out by humans, with their problems now further exacerbated by the barred species's presence. There are ecological discrepancies between the species in areas of sympatry. While both species prefer old-growth forest areas, the spotted owls tend to live in significantly higher elevation areas in Washington's Cascade mountains, with nest sites averaging 966.2 m (3,170 ft) metres above sea level against a mean of 54.1 m (177 ft) for barred owls, in areas with more steep slopes. The barred owls of the area additionally prefer wetter, more variable forest areas, down to riparian zones with limited forested land, while the spotted tended to cluster in more homogeneous upland and ancient coniferous forests. However, little is known on the feasibility or benefits of habitat maintenance that favors spotted over barred owls. Habitat management measures are hypothesized to be insufficient to mitigate the negative effect the barred owls are having. In areas where barred owls moved in within 0.8 km (0.50 mi) of a spotted owl nest area, 39% of spotted owls disappeared and were not seen again, while in areas still free of barred owls (so spared from this interspecific pressure), 11% of spotted owls disappeared and were not found again.
Since the 1960s, barred owls have been expanding their range westward from the eastern US and Canada. While some authors have described the expansion of barred owls into the west as "natural", others state that this is a mischaracterization, as there is little to suggest that the barred owls could have reached the spotted's range without the inadvertent aid of humans— increasing temperatures, wildlife suppression, and tree planting likely facilitated the range increase. When spotted owls and barred owls share the same area, the barred owls generally are more aggressive and out-compete the spotted owls, leading to decreased populations of the native owls. The more aggressive response of barred owls to interspecific stimuli has been verified with experiments incorporating vocalization and owl dummies. Additionally, the adult survival rates appear higher for barred owls (an estimated 91%) than for spotted owls (an estimated 82%). Therefore, the barred owl is considered "demographically superior". Another potential threat is that barred owls and spotted owls occasionally interbreed, creating hybrids ("sparred owl" or "botted owl").  Only 47 hybrids with barred owls (all between female barred owls and male spotted owls) were found in an analysis of more than 9,000 banded spotted owls; consequently, hybridization between these two species is considered to be "an interesting biological phenomenon that is probably inconsequential compared with the real threat—direct competition between the two species for food and space". Most hybrids favor their barred owl heritage with similar and more pale overall coloring than spotted owls, though the back tends to be intermediate in color between the two and the beak coloring is variable. However, there has been much variation described. Due to variances in appearance, previously hybrids between the species were overestimated from field identification, only being certainly identified by genetic loci. Moreover, no recent hybrids could be detected in a survey of the Cascade Mountains.


John James Audubon illustrated the barred owl in Birds of America (published in London, 1827–1838) as Plate 46, where it is shown threatening a grey squirrel. The image was engraved and colored by Robert Havell's London workshops. The original aquatint by Audubon is owned by the Brooklyn Museum.


Strophostyles helvola, commonly called amberique-bean, annual sand bean, or trailing fuzzybean is a species of flowering plant in the legume family. It is native to eastern Canada and the eastern United States.


It is an annual to perennial herbaceous vine, up to 3 m long, with light pubescence on the stem, leaves, and pods. The trifoliate leaves are often divided into three lobes, in a fiddle-shape (panduriform). They possess unique pea-like pink-purple flowers (fading to cream-yellow), with a gradually curving keel petal (the keel petal is one of the most distinguishing characters among the species of the genus). The fruit of S. helvola is up to 10 cm long, containing shiny black seeds with hairy coats originating from the inner surface of the pods. This seed coating lends the seeds buoyancy in water, which is thought to have contributed to its dispersal along major aquatic routes.
Strophostyles helvola is primarily diagnosed by its keel petal (prominent, thin, curving away from the banner at the distal end); long, cylindrical pods; and highly lobed leaves (though not always lobed, and Strophostyles umbellata may also show lobing).


In addition to the type, at least one infraspecific taxon has been recognized, S. helvola var. missouriensis (S. Watson) Britton, although there is little evidence for distinct varieties of this species.
A widely used orthographic variant is Strophostyles helvula, although only the former is taxonomically accepted.


Strophostyles helvola is a wild relative of the cultivated common bean (Phaseolus vulgaris), and could serve as an important model for understanding how herbaceous legumes adapt to different stressful environments. Specifically, S. helvola has coastal populations which show high salinity tolerance due to up-regulated genes.


It is native to eastern Canada and the eastern United States. This bean grows in many habitat types, including disturbed areas, where it is a pioneer species, taking hold in areas where few other plants grow, and in several types of soil, especially sandy types, and it can grow in dry or moist conditions. It can often be found in seaside dune habitat, where arbuscular mycorrhizae help it withstand saline conditions.


This plant was used medicinally and as food by Native American peoples. The Houma people used it to treat typhoid and the Iroquois used it topically for poison ivy irritation and warts. The Choctaw people used the boiled, mashed roots for food. Discovery of large quantities of S. helvola seeds in archaeological sites also suggests a use similar to common bean at one time; though the seeds are smaller than cultivated bean, it is nutritionally similar and possesses the largest seeds and pods for the genus. The pods have been used in the present day as a sauteed vegetable in South Central Mindanao, Philippines.


Strophostyles umbellata, commonly known as the pink fuzzybean or perennial wild bean, is a species of perennial flowering plant in the family Fabaceae. It is native to fields and woods in the southeastern and central United States. It blooms from June to September.
This species is best distinguished from its congeners by its thick, relatively straight keel petal, held close to the banner petal. It also uniquely possesses a perennial, branched caudex at its base. It is most similar morphologically to S. helvola, the differences being that S. helvola has a much thinner keel, curving away more from the banner petal throughout its length. Its leaf morphology can be highly variable, ranging from the highly lobed panduriform shape typical of Strophostyles helvola, to the thin, sericeous, lanceolate leaf typical of S. leiosperma.
Strophostyles umbellata individuals tend to be scattered from one another, which, possibly combined with self-incompatibility, can contribute to their observed low pod set. Like S. helvola, its seeds also possess a cellular, waxy coating, which may aide in buoyancy and water dispersal.


Struthiopteris spicant, syn. Blechnum spicant, is a species of fern in the family Blechnaceae, known by the common names hard-fern or deer fern.  It is native to Europe, western Asia, northern Africa, and western North America. Like some other species in the family Blechnaceae, it has two types of leaves. The sterile leaves have flat, wavy-margined leaflets 5 to 8 millimeters wide, while the fertile leaves have much narrower leaflets, each with two thick rows of sori on the underside.
The Latin specific epithet spicant is of uncertain origin, possibly referring to a tufted or spiky habit.
S. spicant is hardy down to −20 °C (−4 °F) and evergreen, growing to 0.5 m (1 ft 8 in). It has gained the Royal Horticultural Society's Award of Garden Merit.
The species was first described in 1753 by Carl Linnaeus as Osmunda spicant. It has been placed in a wide range of genera, including Blechnum (as Blechnum spicant). In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), it is placed in the genus Struthiopteris, in the subfamily Blechnoideae.


Strymon istapa the mallow hairstreak, mallow-scrub hairstreak, dotted hairstreak or Hewitson's hairstreak. This diurnal butterfly is a widespread species that can be found in xeric habitats throughout the southern United States, Central America, parts of the Caribbean (including Cuba and Grand Cayman), and rarely in South America. This species can be spotted in rural and suburban areas in which human infringement has created open fields or tracks of overgrown weeds as a result of land clearing. These butterflies are often seen rubbing their hindwings together presumably to attract attention to their antenna mimicry scales located on the outer margin of the hindwing.


The gray hairstreak (Strymon melinus) is also called the bean lycaenid or cotton square borer. It is a member of the Lycaenidae family, known as the gossamer-winged butterflies and the second-largest family of butterflies. It is one of the most common hairstreaks in North America, ranging over nearly the entire continent. It also occurs throughout Central America and in northern South America.


The adult gray hairstreak has a wingspan of 20–32 millimetres (0.79–1.26 in). The upper sides of the wings are gray with an orange spot on the hind margin. The underside of the wings are a lighter gray with white and black lines and orange and blue marginal spots near the hind-wings' tail-like extensions.

Caterpillars are green with markings on the sides, covered in short yellow hairs.


The gray hairstreak lives in a wide range of habitats ranging from tropical forests and mountains to temperate woodland areas and meadows, as well as cities and farmland.


The caterpillars of the gray hairstreak butterfly consume a wide range of food plants. However, they do mainly use mallows and legumes as their preferred host plant. They commonly use clovers as their food plant as well, eating rabbit-foot clover (Trifolium arvense), white clover (T. repens), bush clover (Lespedeza capitata), white sweet-clover (Melilotis alba), and Malva neglecta. Young caterpillars are typically found eating flowers and fruiting bodies of their host plant while the older caterpillars eat the leaves.


"NatureServe Explorer 2.0 Strymon melinus Gray Hairstreak". explorer.natureserve.org. Retrieved 3 October 2020.
"Butterflies of Mexico, USA & Canada: Gray Hairstreak". Learn About Butterflies. Retrieved May 10, 2013.
Will, Kip; Gross, Joyce; Rubinoff, Daniel; Powell, Jerry A. (2020). Field Guide to California Insects. Oakland, California: University of California Press. p. 408. ISBN 9780520288744.
"Gray Hairstreak (Mt. Diablo Butterflies) · iNaturalist". iNaturalist. Retrieved 2020-12-04.
"Gray Hairstreak". butterfliesofmassachusetts.net. Retrieved 2020-12-04.


Stylogomphus albistylus, the eastern least clubtail, is a species of dragonfly in the family Gomphidae. It is typically found in North America, particularly in the Appalachians and eastward. It can also be found in the states of Ohio, Michigan, and Wisconsin.
The IUCN conservation status of Stylogomphus albistylus is "LC", least concern, with no immediate threat to the species' survival. The population is stable.


Stylosanthes biflora, known by the common name sidebeak pencilflower, is a species of flowering plant in the legume family. It is native to the Southeastern United States where it is widespread in open areas of native vegetation. It producers yellow-orange flowers in the summer and fall.
This species is highly variable throughout its range, and numerous species had previously been segregated out of it. However, their morphological differences have been found to be so overlapping that the former segregates are now considered the same species.


The brown booby (Sula leucogaster) is a large seabird of the booby family Sulidae, of which it is perhaps the most common and widespread species. It has a pantropical range, which overlaps with that of other booby species. The gregarious brown booby commutes and forages at low height over inshore waters. Flocks plunge-dive to take small fish, especially when these are driven near the surface by their predators. They only nest on the ground, and roost on solid objects rather than the water surface.


The brown booby was described by the French polymath Georges-Louis Leclerc, Comte de Buffon in his Histoire Naturelle des Oiseaux in 1781. The bird was also illustrated in a hand-coloured plate engraved by François-Nicolas Martinet in the Planches Enluminées D'Histoire Naturelle which was produced under the supervision of Edme-Louis Daubenton to accompany Buffon's text. Buffon did not include a scientific name with his description but in 1783 the Dutch naturalist Pieter Boddaert coined the binomial name Pelecanus leucogaster in his catalogue of the Planches Enluminées. The type locality is Cayenne in French Guiana. The current genus Sula was introduced by the French zoologist Mathurin Jacques Brisson in 1760. The word Sula is Norwegian for a gannet; the specific leucogaster is from Ancient Greek leuko for "white" and gastēr for "belly".
There are four recognised subspecies:
S. l. leucogaster (Boddaert, 1783) – Caribbean and Atlantic Islands
S. l. brewsteri Nathaniel Stickney Goss, 1888 – Pacific coasts of USA and Mexico
S. l. etesiaca Thayer & Bangs, 1905 – Pacific coasts of Central America and Colombia
S. l. plotus (Forster, JR, 1844) – Red Sea through the Indian Ocean to the west and central Pacific


The booby's head and upper body (back) is covered in dark brown to black plumage, with the remainder (belly) being a contrasting white. The bare part colours vary geographically, but not seasonally. The species also displays sexual dimorphism of the bare part colours, the males having a blue orbital ring, as opposed to the yellow orbital ring of the female. In addition the male of subspecies S. l. brewsteri is distinctly plumaged in having the forehead, forecrown and chin white, merging to a greyish brown neck and breast.
The female booby reaches about 80 centimetres (31 in) in length, her wingspan measures up to 150 cm (4.9 ft), and she can weigh up to 1,300 g (2.9 lb). The male booby reaches about 75 centimetres (30 in) in length, his wingspan measures up to 140 cm (4.6 ft), and he can weigh up to 1,000 g (2.2 lb).
Unlike other species of sulid the juvenile plumage already resembles that of the adult. They are gray-brown with darkening on the head, upper surfaces of the wings and tail, while the lower breast and underpart plumages are heavily flecked brown on white. Juveniles of subspecies S. l. brewsteri are once again distinct in having the underpart plumage more evenly mouse brown.
Their beaks are quite sharp and contain many jagged edges. They have fairly short wings resulting in a fast flap rate, but long, tapered tails. While these birds are typically silent, bird watchers have reported occasional sounds similar to grunting or quacking.


This species breeds on islands and coasts in the pantropical areas of the Atlantic and Pacific oceans.  They frequent the breeding grounds of the islands in the Gulf of Mexico and the Caribbean Sea. With the rise in pollution in the world, brown boobies have been using marine debris to make their nests. 90.1 percent of these nest were consisted of plastic, while nests near shipwreck have a high percentage of the wreckage debris. This bird nests in large colonies, laying two chalky blue eggs on the ground in a mound of broken shells and vegetation, but usually raises just one chick, the second one to hatch being unable to compete for food with its older sibling, or even ejected from the nest by it. It winters at sea over a wider area.
Brown booby pairs may remain together over several seasons. They perform elaborate greeting rituals, and are also spectacular divers, plunging into the ocean at high speed. They mainly eat small fish (such as flying fish, mullet, halfbeaks, anchovies,goatfish, crowned squirrelfish and Indian mackerel), squid (including the family Ommastrephidae) or shrimp which gather in groups near the surface and may catch leaping fish while skimming the surface. Along with plunge-diving, some fledglings and some adults practice kleptoparasitism, where they steal prey from other seabirds. For example, brown boobies have been observed stealing prey from great frigatebirds as they transfer food to their young. Although they are powerful and agile fliers, they are particularly clumsy in takeoffs and landings; they use strong winds and high perches to assist their takeoffs.


The Eurasian blackcap (Sylvia atricapilla), usually known simply as the blackcap, is a common and widespread typical warbler. It has mainly olive-grey upperparts and pale grey underparts, and differences between the five subspecies are small. Both sexes have a neat coloured cap to the head, black in the male and reddish-brown in the female. The male's typical song is a rich musical warbling, often ending in a loud high-pitched crescendo, but a simpler song is given in some isolated areas, such as valleys in the Alps. The blackcap's closest relative is the garden warbler, which looks quite different but has a similar song.
The blackcap breeds in much of Europe, western Asia and northwestern Africa, and its preferred habitat is mature deciduous woodland. The male holds a territory when breeding, which is defended against garden warblers as well as other blackcaps. The nest is a neat cup, built low in brambles or scrub, and the clutch is typically 4–6 mainly buff eggs, which hatch in about 11 days. The chicks fledge in 11–12 days, but are cared for by both adults for some time after leaving the nest. The blackcap is a partial migrant; birds from the colder areas of its range winter in scrub or trees in northwestern Europe, around the Mediterranean and in tropical Africa. Some birds from Germany and western continental Europe have adapted to spending the winter in gardens in Great Britain and Ireland. Insects are the main food in the breeding season, but, for the rest of the year, blackcaps survive primarily on small fruit. Garden birds also eat bread, fat and peanuts in winter.
Despite extensive hunting in Mediterranean countries and the natural hazards of predation and disease, the blackcap has been extending its range for several decades, and is classified by the International Union for Conservation of Nature as least concern. Its rich and varied song has led to it being described as the "mock nightingale" and it has featured in literature, films and music. In Messiaen's opera Saint François d'Assise, the saint is represented by themes based on the blackcap's song.


The genus Sylvia, the typical warblers, forms part of a large family of Old World warblers, the Sylviidae. The blackcap and its nearest relative, the garden warbler, are an ancient species pair which diverged very early from the rest of the genus at between 12 and 16 million years ago. In the course of time, these two species have become sufficiently distinctive that they have been placed in separate subgenera, with the blackcap in subgenus Sylvia and the garden warbler in Epilais. These sister species have a breeding range which extends farther northeast than all other Sylvia species except the lesser whitethroat and common whitethroat. The nearest relatives of the garden warbler outside the sister group are believed to be the African hill babbler and Dohrn's thrush-babbler, both of which should probably be placed in Sylvia rather than their current genera, Pseudoalcippe and Horizorhinus respectively.
The blackcap was one of the many bird species originally described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae, as Motacilla atricapilla. The current genus name is from Modern Latin silvia, a woodland sprite, related to silva, a wood. The species name, like the English name, refers to the male's black cap. Atricapilla is from the Latin ater, "black", and capillus, "hair (of the head)".
Fossils and subfossils of the blackcap have been found in a number of European countries; the oldest, dated to 1.2–1.0 million years ago, are from the Early Pleistocene of Bulgaria. Fossils from France show that the genus Sylvia dates back at least 20 million years.


The differences between subspecies are small, making subspecific boundaries hard to define, and the exact distribution of S. a. heineken is unclear, since birds from northwest Africa may be of this form. About 2% of male blackcaps on Madeira and the Azores are melanistic, with black plumage on the whole head and upper breast. Melanistic females are rarer, and are characterised by grey-brown underparts. This dark morph has also been recorded from the Canary Islands, but not from Cape Verde. The melanistic birds were formerly sometimes considered to be a distinct subspecies, S. a. obscura.


The blackcap is a mainly grey warbler with distinct male and female plumages. The nominate subspecies is about 13 cm (5.1 in) long with a 7–8 cm (2.8–3.1 in) wing length. The weight is typically 16–25 g (0.56–0.88 oz), but can be up to 31 g (1.1 oz) for birds preparing to migrate. The adult male has olive-grey upperparts, other than a paler grey nape and a neat black cap on the head. The underparts are light grey, becoming silvery white on the chin, throat and upper breast. The tail is dark grey, with an olive tint to the outer edge of each feather. The bill and long legs are grey, and the iris is reddish brown. The female resembles the male, but has a reddish-brown cap and a slightly browner tone to the grey of the upperparts. Juveniles are similar to the female, but their upperparts have a slight rufous tinge, and the breast and flanks have a more olive tone; young males have a darker brown cap than their female counterparts. This species is unmistakable; other dark-headed Sylvia species, such Sardinian and Orphean warblers have extensive black on the head instead of a small cap. They are also larger and have white edges on the tail.
Blackcaps have a complete moult in their breeding areas in August and September prior to migration. Some birds, typically those migrating the greatest distances, have a further partial moult between December and March. Juveniles replace their loosely structured body feathers with adult plumage, starting earlier, but taking longer to complete, than the adults. Blackcaps breeding in the north of the range have an earlier and shorter post-juvenile moult than those further south, and cross-breeding of captive birds shows that the timing is genetically controlled.


The male's song is a rich musical warbling, often ending in a loud high-pitched crescendo, which is given in bursts of up to 30 seconds. The song is repeated for about two-and-a-half minutes, with a short pause before each repetition. In some geographically isolated areas, such as islands, peninsulas and valleys in the Alps, a simplified fluting song occurs, named the Leiern (drawling) song by the German ornithologists who first described it. The song's introduction is like that of other blackcaps, but the final warbling part is a simple alternation between two notes, as in a great tit's call but more fluting. The main song is confusable with that of the garden warbler, but it is slightly higher pitched than in that species, more broken into discrete song segments, and less mellow. Both species have a quiet subsong, a muted version of the full song, which is even harder to separate. The blackcap occasionally mimics the song of other birds, the most frequently copied including the garden warbler and the common nightingale. The main call is a hard tac-tac, like stones knocking together, and other vocalisations include a squeaking sweet alarm, and a low-pitched trill similar to that of a garden warbler.
Male blackcaps will sometimes sing even when incubating, especially with the second brood. This appears to be intended to maintain the bond with the female. Wintering birds in Africa are quiet initially, but start singing in January or February prior to their return north.


The continental breeding range of the blackcap lies between the 14–30° July isotherms, and is occupied by the nominate subspecies, the other forms being restricted to islands or fringe areas in the Caucasus and eastern Iberia. Birds on the Mediterranean and Atlantic islands and in the milder west and south of the main Eurasian distribution often winter within the nesting range, but populations elsewhere are migratory. The blackcap is a leap-frog migrant; birds from the north of the breeding range travel furthest south, whereas Mediterranean breeders move much shorter distances. The wintering areas overlap with the breeding range, but also include extensive areas in West Africa, East Africa south to Lake Malawi, and further north in Ethiopia, South Sudan and Eritrea. The large majority of birds wintering in eastern Africa are of the southwest Asian race, S. a. dammholzi.
There is a migratory divide in Europe at longitude 10–11°E. Birds to the west of this line head southwest towards Iberia or West Africa, whereas populations to the east migrate to the eastern Mediterranean and on to East Africa. Cross-breeding in captivity of birds from the resident population on the Canary Islands with migratory blackcaps from Germany showed the urge to migrate is genetically controlled, the offspring showing intermediate behaviour in terms of restlessness at migration time. Similar experiments using birds from southern Germany and eastern Austria, on opposite sides of the migratory divide, demonstrated that the direction of migration is also genetically determined. Climate change appears to be affecting the migration pattern of the garden warbler and blackcap. Both are arriving in Europe earlier than previously, and blackcaps and juvenile (but not adult) garden warblers are departing nearly two weeks later than in the 1980s. Birds of both species are longer-winged and lighter than in the past, suggesting a longer migration as the breeding range expands northwards.
In recent decades, substantial numbers of continental European birds have taken to wintering in gardens in Great Britain, and, to a lesser extent, Ireland, where the blackcap was formerly just a summer visitor. Although the British climate is sub-optimal, compensatory factors include the ready availability of food, (particularly from bird tables), a shorter migration distance, and the avoidance of the Alps and the Sahara Desert.
It was originally thought that most of these wintering birds come from Germany, and isotope analysis (which enables the wintering location to be determined) showed that the continental birds wintering in Britain tend to mate only among themselves, and do not usually interbreed with those wintering in the Mediterranean or western Africa. This is because the British migrants arrive back on the breeding grounds earlier than blackcaps wintering around the Mediterranean, and form pairs before the southern birds arrive. Mixed pairings are also selected against because the hybrid young would migrate in an intermediate direction, which would take them into the Bay of Biscay.
It now appears that the wintering birds in the UK come from a much wider area than previously thought. The majority come from France, and some individuals come from as far away as Spain and Poland. The steady supply of winter food in gardens gives even Spanish-breeding birds an opportunity to put on weight quicker than in their home range.
A 2021 paper showed that blackcaps, particularly adults, wintering in Britain and Ireland showed high site fidelity and low movement between wintering sites, in contrast to blackcaps wintering in their traditional winter ranges. Adults that frequented gardens had better body condition, smaller fat stores, longer bills, and rounder wing tips. The bill and wing tip shapes reflected a more generalist diet than that of birds in traditional winter sites.
Blackcaps did not exclusively feed in gardens; visits were linked to harsher weather. Individuals generally stayed at garden sites until immediately before spring departure, and supplemental feeding may have benefits for winter survival, When preparing for migration, abundant supplemental food may allow blackcaps to attain better body condition and may facilitate earlier and more successful breeding attempts.
In the Iberian Peninsula, migratory blackcaps (and European robins) track similar climatic conditions over the season, which sedentary individuals must cope with great variation in climate over the year. This suggests a trade-off between the cost of travelling long distances of migrants, and the flexibility required by sedentary individuals to tolerate a wide variety of environmental conditions.


The blackcap's main breeding habitat is mature deciduous woodland, with good scrub cover below the trees. Other habitats, such as parks, large gardens and overgrown hedges, are used as long as they meet the essential requirements of tall trees for songposts and an established understory. Where other Sylvia warblers also breed, blackcaps tend to use taller trees than their relatives, preferably those with a good canopy, such as pedunculate oak. In prime habitat, breeding densities reach 100–200 pairs per square kilometre (250–500 pairs per square mile) in northern Europe, and 500–900 pairs per square kilometre (1,250–2,250 pairs per square mile) in Italy. Densities are much lower in poorer habitats such as conifer forests. Breeding occurs in Europe at altitudes up to 2,200 m (7,200 ft).
The preferred winter habitat around the Mediterranean is scrub and olive orchards, where densities approach the levels found in the best breeding areas. The British wintering population is atypical, with 95% found in gardens, mostly in towns at altitudes below 100 m (330 ft). In Africa, habitats include cultivated land, acacia scrub, mangroves and forest, and these warblers are found at altitudes up to 3,600 m (11,800 ft) in the east of the continent. Wintering birds wander in search of good fruit supplies, but often stay in good feeding areas, and return in subsequent winters. Migrants may occur in a wide variety of habitats, such as reed bed and fen, but show a preference for shrubland.


When male blackcaps return to their breeding areas, they establish a territory. Adults that have previously bred return to the site they have used in previous summers, whereas inexperienced birds either wander until they find a suitable area, or establish a very large initial territory which contracts under pressure from neighbours. Territorial boundaries are established initially by loud singing, performed while the male displays with his crown raised, tail fanned and slow wingbeats. This display is followed, if necessary, by a chase, often leading to a fight. The typical territory size in a French study was 1.12 hectares (2.8 acres), but in insect-rich tall maquis in Gibraltar, the average was only 0.16 hectares (0.40 acres). Females feed within a home range which may overlap other blackcap territories, and covers up to six times the area of the defended zone.
Sylvia warblers are unusual in that they vigorously defend their territories against other members of their genus as well as conspecifics. Blackcaps and garden warblers use identical habits in the same wood, yet aggressive interactions mean that their territories never overlap. Similar songs are a feature of the Sylvia warblers as a group, and it has been suggested that this promotes interspecific competition and helps to segregate territories between related species. It appears more likely from later studies that segregation of sympatric species, other than the blackcap and garden warbler, is due to subtle habitat preferences rather than interspecies aggression.


Blackcaps first breed when they are one year old, and are mainly monogamous, although both sexes may sometimes deviate from this. A male attracts a female to his territory through song and a display involving raising the black crown feathers, fluffing the tail, slow wingbeats, and a short flapping flight. He also builds one or more simple nests (cock nests), usually near his songpost. The final nest, which may be one of the cock nests or built from scratch, is a neat cup of roots, stems and grasses lined with fine material such as hair. The nest is typically 5.5 cm (2.2 in) deep and 10 cm (3.9 in) across, and is built in the cover of bramble, scrubs or trees. It is constructed mainly by the female, and may be up to 4.5 m (15 ft) above the ground, although lower than 1 m (3.3 ft) is more typical. The clutch is typically 4–6 eggs (range 2–7), which are usually buff with grey and brown blotches and a few dark brown spots. The average size of the egg is 19.7 mm × 14.7 mm (0.78 in × 0.58 in).
The eggs are incubated for an average of 11 days (range 10–16). Both adults incubate, although only the female stays on the nest at night. The chicks are altricial, hatching naked and with closed eyes, and are fed by both parents. They fledge about 11–12 days after hatching, leaving the nest shortly before they are able to fly. They are assisted with feeding for a further two or three weeks. If the nest is threatened, the non-incubating bird gives an alarm call so that the sitting parent and chicks stay still and quiet. A male blackcap may mob a potential predator, or try to lure it away with disjointed runs and flaps on the ground. The blackcap normally raises just one brood, but second nestings are sometimes recorded, particularly in the milder climate of the Mediterranean and the Atlantic islands; triple brooding has been observed once, the female laying a total of 23 eggs in the season.
Of eggs laid, 65–93% hatch successfully, and 75–92% of the chicks go on to fledge. The productivity (young fledged per nest) varies with location, level of predation and quality of habitat, but the national figure for the UK was 2.5. The adult annual survival rate is 43% (males 46%, females 29%), and 36% of juveniles live through their first year. The typical life expectancy is two years, but the record is 13 years and 10 months for a bird in the Czech Republic.


The blackcap feeds mainly on insects during the breeding season, then switches to fruit in late summer, the change being triggered by an internal biological rhythm. When migrants arrive on their territories they initially take berries, pollen and nectar if there are insufficient insects available, then soon switch to their preferred diet. They mainly pick prey off foliage and twigs, but may occasionally hover, flycatch or feed on the ground. Blackcaps eat a wide range of invertebrate prey, although aphids are particularly important early in the season, and flies, beetles and caterpillars are also taken in large numbers. Small snails are swallowed whole, since the shell is a source of calcium for the bird's eggs. Chicks are mainly fed soft-bodied insects, fruit only if invertebrates are scarce.
In July, the diet switches increasingly to fruit. The protein needed for egg-laying and for the chicks to grow is replaced by fruit sugar which helps the birds to fatten for migration. Aphids are still taken while they are available, since they often contain sugars from the plant sap on which they feed. Blackcaps eat a wide range of small fruit, and squeeze out any seeds on a branch before consuming the pulp. This technique makes them an important propagator of mistletoe. The mistle thrush, which also favours that plant, is less beneficial since it tends to crush the seeds. Although any suitable fruit may be eaten, some have seasonal or local importance; elder makes up a large proportion of the diet of northern birds preparing for migration, and energy-rich olives and lentisc are favoured by blackcaps wintering in the Mediterranean.
The continental birds wintering in British gardens rely on provided food, and the major items are bread and fat, each making up around 20% of the diet; one bird survived the whole winter eating only Christmas cake. Fruit is also eaten, notably cotoneaster (41% of the fruit consumed), ivy and honeysuckle, and apple if available. Some birds have learned to take peanuts from feeders. Blackcaps defend good winter food sources in the wild, and at garden feeding stations they repel competitors as large as starlings and blackbirds. Birds occasionally become tame enough to feed from the hand.


Blackcaps are caught by Eurasian sparrowhawks in the breeding range, and by Eleonora's falcons on migration. Eurasian jays and Eurasian magpies take eggs and young, as do mammals such as stoats, weasels and squirrels. Domestic cats are the most important predator, possibly killing up to 10% of blackcaps. Blackcaps are occasionally hosts of the common cuckoo, a brood parasite. The level of parasitism is low because the cuckoo's eggs are often rejected. Blackcaps have evolved adaptations which make it difficult for the parasitic species to succeed, despite the cuckoo's tendency to lay eggs which resemble those of their host. Blackcaps are good at spotting alien eggs, and their own eggs are very alike within a clutch, making it easier to spot the intruder. There is, however, considerable variation between different clutches, making it harder for the cuckoo to convincingly mimic a blackcap egg. The open habitat and cup nest of the warbler make it a potential target for the cuckoo; it may have experienced much higher levels of parasitism in the past, and countermeasures would have spread rapidly once they evolved.
The only blood parasites found in a study of blackcaps trapped on migration were protozoans from the genera Haemoproteus and Plasmodium. The study concluded that 45.5% of the males and 22.7% of the females were affected, but the number of parasites was small, and the ability to store fat for the migration flight was unimpaired. Seventeen strains of H. parabelopolskyi are found only in the blackcap, and form a monophyletic group; three further members of that group are found only in the garden warbler, and another three occur in the African hill babbler, supporting the shared ancestry of the three bird species. The protozoan Isospora ashmoonensis was first identified in a blackcap in Egypt. Blackcaps may carry parasitic worms that sometimes kill their hosts. External parasites include chewing lice and feather mites. The latter do little damage, although heavy infestations cause individual tail feathers to develop asymmetrically.


Aristotle, in his History of Animals, considered that the garden warbler eventually metamorphosed into a blackcap. The blackcap's song has led to it being described as the "mock nightingale" or "country nightingale", and John Clare, in "The March Nightingale" describes the listener as believing that the rarer species has arrived prematurely. "He stops his own and thinks the nightingale/Hath of her monthly reckoning counted wrong". The song is also the topic of Italian poet Giovanni Pascoli's "La Capinera" [The Blackcap].
Giovanni Verga's 1871 novel Storia di una capinera, according to its author, was inspired by a story of a blackcap trapped and caged by children. The bird, silent and pining for its lost freedom, eventually dies. In the book, a nun evacuated from her convent by cholera falls in love with a family friend, only to have to return to her confinement when the disease wanes. The novel was adapted as films of the same name in 1917, 1943 and 1993. The last version was directed by Franco Zeffirelli, and its English-language version was retitled as Sparrow. In Saint François d'Assise, an opera by Messiaen, the orchestration is based on bird song. St Francis himself is represented by the blackcap.
Folk names for the blackcap often refer to its most obvious plumage feature (black-headed peggy, King Harry black cap and coal hoodie) or to its song, as in the "nightingale" names above. Other old names are based on its choice of nesting material (Jack Straw, hay bird, hay chat and hay Jack). There is a tradition of the Royal Navy's Fleet Air Arm bases being named for birds. A former base near Stretton in Cheshire was called HMS Blackcap.


The blackcap has a very large range, and its population in Europe is estimated at 41–65 million breeding pairs. Allowing for birds breeding in Africa and Asia, the total population estimate is between 101 and 161 million individuals. It is therefore classified by the International Union for Conservation of Nature as being of least concern.
Blackcaps and other small birds are illegally trapped and hunted in large numbers in Mediterranean countries, particularly in Lebanon, Syria, Palestine, Malta, Libya, Egypt and Cyprus, where they are considered as a delicacy. Despite hunting and natural hazards, the European population of the blackcap has been rising for several decades as the range extends northwards, for example to Scotland and Denmark. There are occasional nesting records from outside the main range, such as in northern Israel and the Faroes, and wandering birds may appear further afield in Iceland or on the islands of Arctic Russia. In the Baltic, the spread of the blackcap appears to have been helped by the availability of territories formerly occupied by the declining barred warbler.


The table is based on Baker (1997). Parentheses indicate that the scientific name has changed from that originally given.
Hatching; Italy 65%; UK 76%, eastern Germany 93%. Fledging; Italy 75%; UK 80%, eastern Germany 92%.


The garden warbler (Sylvia borin) is a common and widespread small bird that breeds in most of Europe and in the Palearctic to western Siberia. It is a plain, long-winged and long-tailed typical warbler with brown upperparts and dull white underparts; the sexes are similar and juveniles resemble the adults. Its two subspecies differ only slightly and interbreed where their ranges overlap. Due to its lack of distinguishing features, this species can be confused with a number of other unstreaked warblers. The garden warbler's rich melodic song is similar to that of the blackcap, its closest relative, which competes with it for territory when nesting in the same woodland.
The preferred breeding habitat in Eurasia is open woodland with dense low cover for nesting; despite its name, gardens are rarely occupied by this small passerine bird. The clutch of four or five blotched cream or white eggs is laid in a robust cup-shaped nest built near the ground and concealed by dense vegetation. The eggs are incubated for 11–12 days. The chicks are altricial, hatching naked and with closed eyes, and are fed by both parents. They fledge about 10 days after hatching. Only about a quarter of young birds survive their first year. The garden warbler is strongly migratory, wintering in sub-Saharan Africa. A wide range of habitats are used in Africa, but closed forest and treeless Sahel are both shunned. Insects are the main food in the breeding season, although fruit predominates when birds are fattening prior to migration, figs being a particular favourite where available. These warblers have a mixed diet of insects and fruit in their African wintering grounds.
The garden warbler is hunted by Eurasian sparrowhawks and domestic cats, and its eggs and nestlings are taken by a variety of mammalian and avian predators. It may be host to various fleas, mites and internal parasites, and it is a host of the common cuckoo, a brood parasite. The large and fairly stable numbers and huge range of the garden warbler mean that it is classed as least concern by the International Union for Conservation of Nature. Despite a small population decline in much of its European range, the bird's breeding distribution is expanding northwards in Scandinavia.


The genus Sylvia, the typical warblers, forms part of a large family of Old World warblers, the Sylviidae. Fossils from France show that the genus dates back at least 20 million years. The garden warbler and its nearest relative, the blackcap, are an ancient species pair which diverged very early from the rest of the genus, between 12 and 16 million years ago. In the course of time, these two species have become sufficiently distinctive that they have been placed in separate subgenera, with the blackcap in subgenus Sylvia and the garden warbler in Epilais. These sister species have a breeding range which extends farther northeast than all other Sylvia species except the lesser whitethroat and common whitethroat.
The nearest relatives of the garden warbler outside the sister group are believed to be the African hill babbler and Dohrn's thrush-babbler.
The garden warbler was given the binomial name Motacilla borin by the Dutch naturalist Pieter Boddaert in 1783. The current genus name is from Modern Latin silvia, a woodland nymph, related to silva, a wood. The specific borin is derived from a local name for the bird in the Genoa area of Italy; it derives from the Latin bos, ox, because the warbler was believed to accompany oxen.
There are two recognised subspecies.
Sylvia borin borin (Boddaert, 1783), the nominate subspecies, breeds in western, northern and central Europe to Finland, central Poland, western Hungary and Bosnia.
S. b. woodwardi (Sharpe, 1877), named for Sharpe's collaborator Bernard Barham Woodward, breeds in eastern Europe and temperate Asia east to western Siberia.
Intermediate birds occur where the recognised forms meet and interbreed, and have sometimes been given subspecies status, including S. b. kreczmeri in Poland and S. b. pateffi in Bulgaria, but these are not generally accepted as valid taxa.


The garden warbler is 14 cm (5.5 in) long with a 7.6–8.4 cm (3.0–3.3 in) wing length. The weight is typically 16–22 g (0.56–0.78 oz), but can be up to 35.5 g (1.25 oz) for birds preparing to migrate. It is a plain, long-winged and long-tailed bird with unstreaked olive-brown upperparts and dull white underparts. It has a whitish eyering and a faint pale supercilium, and there is a buff wash to the throat and flanks. The eye is black, the legs are bluish-grey and the strong bill has a grey upper and paler grey lower mandible. The male and female are indistinguishable by external appearance including size. Juveniles have a looser plumage than an adult, with paler and greyer upperparts and a buff tone to the underparts. The eastern subspecies S. b. woodwardi is slightly larger and paler than the nominate form with a greyer tone to the upperparts and whiter underparts. The subspecies are hard to distinguish visually where they occur together in Africa, but a wing length greater than 80 mm (3.1 in) confirms S. b. woodwardi when birds are trapped.
The plain appearance of the garden warbler means that it can be confused with several other species. The melodious and icterine warblers usually have long bills and a yellowish tint to their plumage. The booted warbler is similar in colour, although it is smaller, more delicately built and has a flesh-coloured bill. Western and eastern olivaceous warblers are also relatively small, and have white outer tail feathers as well as a pinkish bill. Juvenile barred warblers, which lack the obvious barring of adults, are much larger than garden warblers and have a pale double wingbar.
Juvenile garden warblers have a partial moult mainly involving the body plumage between June and September prior to migration. Adults also have a similar, but sometimes more extensive, partial moult in late summer, and a complete moult in their African wintering areas before the return migration.


The male's song, usually delivered by birds in dense cover, is a rich musical warbling usually delivered in bursts of a few seconds duration, but sometimes for longer periods. The song is confusable with that of the blackcap, although compared to that species it is slightly lower-pitched, less broken into discrete song segments and more mellow. Both species have a quiet subsong, a muted version of the full song, which is much more difficult to separate. The most frequent call of the garden warbler is a sharp kek-kek, which is repeated rapidly when the bird is alarmed. A quiet rasping tchurr-r-r-r resembling the main call of the common whitethroat is also sometimes heard. The juvenile has a quia alarm vocalisation. Subsong may be heard on the wintering grounds in Africa, developing into the full song in March and April prior to the return to Europe.


The garden warbler breeds in most of Europe between the 12–28 °C (54–82 °F) isotherms and east across temperate Asia to the Yenisei River in Siberia. Its range extends further north than any other Sylvia warbler. All populations are migratory, wintering in sub-Saharan Africa as far south as South Africa. Birds from central Europe initially migrate to the southwest, reorientating to the south or southeast once in Africa, although Scandinavian migrants may head south through the Alps and across the Mediterranean Sea. S. b. woodwardi reaches Africa by a more easterly route, many birds passing through the Arabian Peninsula. When garden warblers cross the Sahara, they fly at night, resting motionless and without feeding in suitable shade during the day. During their journey, they can metabolise not only body fat but also up to 19% of their breast and leg muscles and 39% of their digestive tract. Many birds pause for a few days to feed after the desert crossing before continuing further south.
The nominate subspecies occurs in the western and central parts of the winter range, although some birds occur as far east as Kenya. S. b. woodwardi winters in eastern and southern Africa. Movements in Africa are poorly known, although at least some birds return to the same location in subsequent years. There are only a handful of records of birds recorded in Europe in winter, from Corsica, the UK and Ireland. Spring migration routes are poorly known, but appear to lie more directly across the Mediterranean. This warbler has occurred as a vagrant in Afghanistan, Djibouti, Iceland, São Tomé and Príncipe, Somalia, Yemen, Svalbard, Jan Mayen and Madeira.
The breeding habitat of the garden warbler is open areas with dense bushes, including thickets and woodland edges. Shady areas and a bushy or herbaceous undergrowth are preferred, as are woods adjacent to rivers or reed beds; in Ireland it favours thickets on the shores of small lakes. A tolerance of willow, alder and birch allows it to breed farther north and at higher altitudes than any other European Sylvia warbler. Mature conifers and dense plantations are avoided, although young conifer plantations with thick undergrowth are suitable for nesting. Despite its name, it is not a bird of gardens. In Africa, a wide range of habitats with trees are used, although closed forests and arid areas are again avoided. This warbler occurs at altitudes of up to 2,600 m (8,500 ft) in suitable mountain woodland, although in East Africa it is usually found at a lower altitude than the blackcap, and in moister areas than the common whitethroat.


Garden warblers first breed when they are one year old, and are mainly monogamous, although the male at least may sometimes deviate from this. When males return to their breeding areas, they establish a territory. Sylvia warblers are unusual in that they vigorously defend their territories against other species in their genus as well as conspecifics. Blackcaps and garden warblers use identical habits in the same woods, yet aggressive interactions mean that their territories never overlap. Similar songs are a feature of the Sylvia warblers as a group, and it has been suggested that this promotes interspecific competition and helps to segregate territories between related species. However, it appears more likely from later studies that segregation of sympatric species, other than the blackcap and garden warbler, is due to subtle differences in habitat preferences rather than interspecies aggression. There are typically 3–9 territories per hectare (1.2–3.6 per acre), but in prime habitat, such as moist willow or birch woodland or young deciduous regrowth, there may be more than 10 pairs per hectare (4 per acre). Individual territories are similar in size to those of blackcaps at 0.2–0.76 ha (0.49–1.88 acres).
A male attracts a female to his territory through song and a display which involves rapid wing beating while perched. He will also build a number of simple nests (cock's nests) to show to his mate, although only rarely will she complete the structure, usually starting afresh. The nest is concealed in vegetation, the nature of which depends on local availability. Rubus species are commonly used in temperate regions, with willow predominating in alpine valleys. Sometimes, particularly in stinging nettles, the nest may be built around a number of vertical stems, in the manner of a reed warbler. The nest is normally between 0.3 and 1.2 m (0.98 and 3.94 ft) above the ground, and very rarely higher than 2 m (6.6 ft). The nest is a cup of dry grass, moss and twigs, with a soft lining of finer plant material or hair. It is larger and heavier than a blackcap's nest, averaging 8.3 cm (3.3 in) high and 11.2 cm (4.4 in) wide with a cup 5.5 cm (2.2 in) deep and 6.3 cm (2.5 in) wide.
The first eggs are laid in late April in southern Germany, early May in northwest Europe, and late May in Finland. The season is prolonged with some birds nesting as late as July. The clutch is typically four or five eggs (range two to six), which are usually whitish or buff with grey, purple and brown blotches. The average size of the egg is 20 mm × 15 mm (0.79 in × 0.59 in), and it weighs 2.2 g (0.078 oz), of which 6% is shell. The eggs are incubated for 11–12 days by both adults, although only the female stays on the nest at night. The chicks are altricial, hatching naked and with closed eyes, and are fed by both parents. They fledge about 10 days after hatching (range 9–12), leaving the nest shortly before they are able to fly. They are assisted with feeding for a further two weeks, and the family may stay together for a few days after that. The short incubation and fledging times may be a result of predation pressure, the rapid development of the chicks enabling them to leave the vulnerable nest as early as possible, even while still flightless. This avoids the possible loss of an entire brood, but means that the adults must provide food to the young for a significant period until they can fend for themselves. One brood per year is normal, although a few second broods are known.
The southward migration starts in mid-July, with larger numbers departing in August and peaking in early September. Most adults have gone by mid-September, although juveniles may linger for another month.
On average, just over 50% of breeding pairs are successful in producing at least one fledged young from a nest, with early breeding and low population density being factors increasing success. In the UK, more than 50% of the failures are due to predation and about 30% result from food shortages in bad weather. The annual survival rate is about 50% for adults and 26% for juveniles in their first year. The typical lifespan is two years, but a bird in Sweden lived to ten years and two months. Much greater ages, up to 24 years, have been recorded in captive garden warblers.


The garden warbler feeds mainly on insects in the breeding season, although other small invertebrates such as spiders are also eaten. It picks its prey off leaves and twigs, sometimes hovering to do so. It normally forages at less than 6 m (20 ft) above the ground. After nesting, there is a genetically controlled switch to a fruit diet, although insects are still consumed while the birds fatten prior to migration; birds gain weight more rapidly from a diet containing both fruit and insects than either alone. Berries and other soft fruit are preferred, and figs are particularly important for birds preparing to migrate. This predilection gives rise to the Italian beccafico (fig pecker) and Portuguese felosa-das-figueiras (fig-tree warbler) as names for this species. On this diet a bird can gain weight quickly and the liver increases the rate at which it produces fatty acids for storage in adipose tissue.
In Africa, the warbler eats insects as well as berries, and the fruits of the introduced Spanish flag is a favourite where present. An increase in body mass occurs again before the northward migration, birds fattening even more rapidly than prior to their southward journey. Most internal organs (including the liver, spleen, intestines, kidneys and heart) and the flight muscles lose weight during the journey over the Sahara, although the testes quadruple in mass in preparation for the breeding season. Unlike drier-habitat species like the common whitethroat, they leave from savanna rather than the treeless Sahel further north.
Fruit is normally picked by a perched bird, although there is a record of a mulberry fruit being taken in flight. Garden warblers often feed with conspecifics and other fruit-eating passerines. Over 35 plant species have been recorded as food for this warbler just in central Europe, with many additional species being consumed in the Mediterranean region and on the African wintering grounds.


The main predators of the garden warbler are Eurasian sparrowhawks and domestic cats. Some falcons will also take adults, and the Eleonora's falcon hunts the garden warbler and many other small passerines as they migrate across the Mediterranean. Eurasian jays and Eurasian magpies take the eggs and young of warblers, as do mammals such as stoats, weasels and squirrels. The garden warbler is a host of the common cuckoo, a brood parasite. The blackcap has a much lower level of parasitism than its relative because the cuckoo's eggs are often rejected.
External parasites of the garden warbler include the fleas Ceratophyllus gallinae and Dasypsyllus gallinulae and the mite Syringophilosis borini, named after its host. Two species of protozoan parasites in the genus Isospora occur in garden warblers, I. sylvianthina and I. sylviae. Samples from two sites showed infection levels above 74% and 28% respectively for the two species. The extent of infection does not impact on the bird's body mass or the amount of body fat. Three strains of another protozoan, Haemoproteus parabelopolskyi are found only in the garden warbler, and form a monophyletic group. Seventeen further members of that group are found only in the blackcap, and another three occur in the African hill babbler, supporting the shared ancestry of the three bird species.


The garden warbler has a very large range of 9,650,000 km² (3,730,000 sq mi), and its population in Europe is estimated at 17–31 million breeding pairs. Allowing for birds breeding in Asia, the total population is between 54 and 124 million individuals. There is no evidence of any serious decline in numbers, so it is classified by the International Union for Conservation of Nature as being of least concern.
There has been a slight decline in numbers in Europe since 1980, although the Scandinavian population is growing. Climate change appears to be affecting the migration pattern of the garden warbler and blackcap. Both are arriving in Europe earlier than previously, and blackcaps and juvenile (but not adult) garden warblers are departing nearly two weeks later than in the 1980s. Birds of both species are longer-winged and lighter than in the past, suggesting a longer migration as the breeding range expands northwards.


In his History of Animals, Aristotle considered that the garden warbler eventually metamorphosed into a blackcap. The composer Olivier Messiaen used the song of the garden warbler as the basis for his 1971 solo piano piece La fauvette des jardins, the title being the French name of the species. His Turangalîla-Symphonie, a major work inspired by the legend of Tristan and Iseult, has a summer garden scene as its sixth movement. This features the song of the warbler, along with those of the nightingale and blackbird.
The garden warbler is prized as a gastronomic delicacy in Mediterranean countries. French epicure Jean Anthelme Brillat-Savarin said of the warbler when cooked like ortolan bunting "if it were the size of a pheasant, it would be worth an acre of land". An Italian stuffed sardine dish sarde a beccafico derives its name from its supposed resemblance to the cooked birds, known in that country as beccafico, fig-pecker.
Old names for the garden warbler, such as strawsmear, small straw and haychat, are often derived from its choice of nesting material, although the commonest of the English folk names was "pettychaps". These names were often shared with other warblers including the blackcap, common whitethroat and common chiffchaff.


The lesser whitethroat (Curruca curruca) is a common and widespread typical warbler which breeds in temperate Europe, except the southwest, and in the western and central Palearctic. This small passerine bird is strongly migratory, wintering in Africa just south of the Sahara, Arabia and India.
Unlike many typical warblers, the sexes are almost identical. This is a small species with a grey back, whitish underparts, a grey head with a darker "bandit mask" through the eyes and a white throat. It is slightly smaller than the common whitethroat, and lacks the chestnut wings and uniform head-face color of that species. The lesser whitethroat's song is a fast and rattling sequence of tet or che calls, quite different from the common whitethroat's scolding song.
Like most "warblers", it is insectivorous, but will also take berries and other soft fruit. This is a bird of fairly open country and cultivation, with large bushes for nesting and some trees. The nest is built in low shrub or brambles, and 3 to 7 eggs are laid.