28 August 2001
Prepared by: Susan Yasuda, USDA Forest Service, Eldorado National Forest, Placerville Ranger District, 4260 Eight Mile Road, Camino, CA 95709
SPECIES: Flammulated Owl (Otus flammeolus)
McCallum (1994b) describes six subspecies for the flammulated owl including Otus flammeolus flammeolus.
Otus flammeolus rarus - based on two specimens from Guatamala,
however, thought to be captured while migrating, and possibly from southern
Mexico or the Pacific Northwest. Johnsgard (1988) considers this to be an invalid
subspecies based on the specimens collected from wintering grounds.
Otus flammeolus idahensis - based on a specimen with a short wingspan from the northern United States.
Johnsgard (1988) considers it from British Columbia.
Otus flammeolus borealis - northern subspecies with plumage duller than idahensis or rarus.
Otus flammeolus frontalis - Colorado Front Range subspecies with plumage browner than flammeolus with dark black streaks in the shafts.
Otus flammeolus meridionalis - smaller subspecies with
glossier plumage than rarus from Guatemala, though Johnsgard (1988) considers
it also from Mexico.
No special status in California.
Global Rank 4
RANGE IN CALIFORNIA:
1. Historical References
Flammulated owls occur in the western United States and occupy most of Oregon, Washington, Utah, Nevada, Arizona, and New Mexico. The species also exists in montane regions of California, western Colorado, and central Mexico, and has small populations in Baja California, Idaho, and British Columbia (Johnsgard 1988). The breeding range covers over nine hundred thousand square miles with about ten percent occurring in California (USDA, 1994).
2. Current Breeding Distribution
Flammulated owls breed from southern British Columbia
south through the western United States (Zeiner et al. 1990). In California,
it is found in summer thoughout the Cascades, Sierra Nevada, forested parts
of the coast ranges from Del Norte County south to Monterey County, the Transverse
Ranges, the Peninsular Ranges (Winter 1974), the Klamath Ranges (Zeiner et al.
1990), and all national forests (Timossi 1990) where suitable habitat exists.
The breeding range is limited to the higher parts of the yellow pine (ponderosa
pine) belt, between elevations of 366 m (1200 ft) to 1676 m (5500 ft) in the
north, and up to 2743 m (9000 ft) in the southern part of its range (Winter
1. Average Territory Size/Home Range
Territories vary from 1.6 to 4 ha (4-10 acres) in size, with diameters rarely exceeding 274 m (890 ft), and are defended only by the adult males in May and June (Zeiner et al. 1990). They may be distributed singly, but are more often in small groups (Reynolds and Linkart 1987a, Ziner et al. 1990) causing some to believe that flammulated owls nest in colonies (Johnsgard 1990), however, not all researchers support this theory (Reynolds and Linkart 1987a, Palmer 1988, McCallum 1994b).
Home range size is not well defined but seems to vary from 5-20 ha (12 to 50 ac) (Zeiner et al. 1990) and appears to be dependent on the degree of patchiness and age of overstory trees with home range increasing with a decrease in amount of suitable habitat components. Home range shape is determined by the topography of the area and the existence of neighboring home ranges (Johnsgard 1988). Breeding densities vary from 3.2 to 5.2 adult males per 100 ha (247 ac) (Ziener et al. 1990). Ranges of females are not known but are probably smaller, as females are fed by males during incubation and the early nesting period (McCallum 1994b). A study in Oregon, showed a reduction in the male home range from 16 ha (39 ac) during the incubation stage to 7.9 ha (20 ac) during the nestling period, possibly to decrease time between feeding visits (McCallum 1994b).
Flammulated owls show significant site fidelity (about 50% return rate) with the males being more faithful than the females. The females have a higher tendency to disperse, but usually only move to adjacent territories, which correspond to dispersal distances of about 425 m (1394 ft) (Reynolds and Linkart 1987a). The young leave the home ranges of their parents at about the age of 8 weeks, which is usually only shortly before fall migration starts in October. Their dispersal distance on the breeding grounds the following spring is not known (Johnsgard 1988).
2. Time of Occurrence and Seasonal Movements
Flammulated owls migrate at night to winter from Mexico to Guatamala (Zeiner et al. 1990) and El Salvador, casually north to southern California (AOU 1983). The flammulated owl summers from British Columbia south to southern Mexico and winters from southern Mexico to El Salvador, migrating southward in the lowlands mainly in October, and northward in April. The species occurs year-round in a semiarid cool temperature climate and leaves the northern part of its range during winter, when the adult lepidopterans, coleopterans, and orthopterans it eats are unavailable. The exceptions to this pattern are the few fall and winter records from the southern United States (McCallum 1994b).
Arrival in California occurs around the second week of April and departure is near the end of October (Phillips 1942, Winter 1974). Some females arrive on breeding grounds as early as males, but others appear later (Reynolds and Linkart 1987b). Virtually nothing is known about the species range, habitat or diet in winter (McCallum 1994b).
Natal dispersal begins in August, when young stop roosting together. Brood division may assist in predator avoidance due to conspicuous begging from young at night as well as multiple predation by diurnal predators if located at one roost. Studies that tracked nestlings did not detect them returning to the area they were banded. More research and nest searches in outlaying areas around the study areas were indicated as needed to determine if young are returning to the local area (McCallum 1994b).
3. Nest Type
Flamulated owls are secondary cavity nesters and rely on nest cavities previously excavated by woodpeckers, most often by pileated woodpeckers (Bull et al. 1990) and northern flickers.
4. Foraging Strategy
The flammulated owl's preference for yellow pine and/or Douglas-fir has been linked to prey availability as there are four times as many lepidopteran (moth and butterfly) species associated with Douglas-fir and ponderosa pine than other common western conifers. Both high prey diversity and structure of these forest types may favor successful foraging by flammulated owls primarily in open mature forests versus dense even-aged stands. Foraging occurs in the open upper two-thirds of tree crowns, between trees and on the ground (McCallum 1994b).
Flammulated owls feed primarily on insects which they capture in the air by "hawking" (Ehrlich et al. 1988), on the ground or trees by pouncing from a nearby perch (Richmond et al. 1980) or gleaning them from trunks or branches (Zeiner et al. 1990). Hunting occurs mainly at dawn and dusk with less activity occurring in the middle of the night (Marshall 1957).
Males utilize territorial song posts associated with large diameter (Reynolds and Linkart 1987a) ponderosa pine and Douglas-fir in open mixed conifer stands (averaging 289 years of age) to attract females and defend their territories from other males (McCallum 1994b, Reynolds and Linkart 1987a). Radio tracked birds blended in by sitting next to tree trunks or in dense clumps of foliage. Mated pairs move through their home range with males entering and calling from cavities with the female following the male into a cavity, presumably selecting a nest in the process (McCallum 1994b).
6. Mating Systems
Flammulated owls are long-lived, low fecundity species, monogamous breeders (Erhlich 1988, McCallum 1994b). Unmated males may continue to sing throughout the summer, however, their presence does not increase the current population but instead serves as a buffer against future declines by providing potential breeding males in an area. Peak activity for breeding occurs in June and July (Zeiner et al. 1990) with pair formation occurring as late as June (McCallum 1994b).
7. Clutch Size
There is typically only one clutch per year (McCallum 1994b) with two to three eggs (Johnsgard 1988, Zeiner et al. 1990) however, Marti (1997) indicates that four egg clutch sizes happen but appear to be rare.
8. Incubating Sex
The female does all of the incubation (Johnsgard 1988, Zeiner et al. 1990).
9. Incubation Period
Incubation, lasts about 26 (Johnsgard 1988, Zeiner et al. 1990) to 28 days (Erhlich 1988). Hatching occurs in June and July based on studies from New Mexico, Colorado and Idaho (McCallum 1994b). Data from studies in California were lacking on natural cavities but would possibly be similar to this based on elevation and time of arrival. Hatching occurred during the month of June in an artifically constructed cavity, in the form of a nestbox, on the Eldorado National Forest, in northern California (USDA 2001).
10. Nestling Period
About 22-25 days after hatching, the young leave the nest (Johnsgard 1988, Zeiner et al. 1990), with the fledgling period lasting approximately 25-32 nights (McCallum 1994b).
11. Development at Hatching
Erhrlich (1988) describes the owlets as semiprecocial,
indicating the young are hatched immobile, eyes
closed, downy and fed by adults.
12. Number of Broods
An average of 2.4 young are fledged per nesting attempt, with majority of nests that are successful fledging all of their young (Johnsgard 1988). First nesting year birds have a lower reproductive success (.25 fewer young) than pairs in which at least one parent was known to have nested previously. Flammulated owls may double clutch if thier first brood is lost early in the season (Reynolds and Linkart 1987a).
13. Who Tends Young
The male is the sole provider for the incubating female, as well as the young until well into the nestling period (Johnsgard 1988, Zeiner et al. 1990). After the twelth night of hatching, both parents will begin to forage and deliver food to the young (Johnsgard 1988, McCallum 1994b).
1. Nest Site
a. Nest Substrate
The owls selectively nest in dead ponderosa pine snags, and prefer nest sites with fewer shrubs in front than behind the cavity entrance, possibly to avoid predation and obstacles to flight. Flammulated owls will nest only in snags with cavities that are deep enough to hold the birds, and far enough off the ground to be safe from terrestrial predators. The cavity is typically unlined, 28-31 cm (11 to 12 in) deep with the average depth being 21.2 cm (8.4 in) (McCallum and Gehlbach 1988). California black oak may also provide nesting cavities, particularly in association with ridge tops and xeric mid-slopes, with two layered canopies, tree density of 1270 trees/ha (2.5 ac), and basal area of 58 m(sq)/ha (624 ft(sq)/2.5ac) (McCallum 1994b). Flammulated owls will also occupy nestboxes ((Marti 1997).
b. Height of Nest
The nest is usually 1-12 m (3-39 feet) above the ground (Zeiner et al. 1990) with 4.9 m (16 feet)
being the average height of the cavity entrance (McCallum and Gehlbach 1988).
c. Height or Size of Nest Plant
Flammulated owls in coniferous forests tend to prefer large diameter trees with a diameter at breast height of 50 cm (20 in) (USDA 1994).
d. Plant Species Concealing Nest
In California, the species breeds in conifer habitats from ponderosa pine up to red fir forests
(Verner and Boss 1980) with a strong association with late seral ponderosa pine forests,
mixed with California black oak and Douglas-fir (USDA 1994).
e. Percent Nest Cover
Nest occurs within a cavity offering total cover minus the entrance hole.
2. Vegetation Surrounding the Nest
a. Canopy Cover
Flammulated owls nest in habitat types with low to intermediate canopy closure (Zeiner et al. 1990). They prefer to forage in older stands that support understories, and need slightly open canopies and space between trees to facilitate easy foraging. The open crowns and park-like spacing of the trees in old growth stands permit the maneuverability required for hawk and glean feeding tactics (USDA 1994).
b. Dominant Plant Species in Canopy
Nesting cavities are typically found in ponderosa pine forests, however, the flammulated owl will use other tree species including aspen. In the western Sierra Nevada, the Wildlife Habitat Relationship (WHR) database lists ponderosa pine, black oak woodland, mixed conifer, Jeffrey pine, red fir, and lodgepole pine as the habitats used by flammulated owls (Verner and Boss 1980, Zeiner et al. 1990). A nesting record from the Argus Mountains of California was in an old pinyon forest (McCallum 1994b).
Studies in several states, including California show owl territories tend to be on south slopes,
ridgetops and plateaus, where ponderosa pine and Douglas-fir occurs (McCallum 1994b). The
owls also seem to prefer nest sites on ridges, on the upper third of slopes, and on east or south
facing slopes (Bull et al. 1990).
d. Tree DBH
Owls nested on slopes with stands of trees whose average diameter at breast height (dbh) are
greater than 50 cm (20 in) (Bull et al. 1990).
e. Snags, Stumps and Logs
Flammulated owls are obligate secondary cavity nesters (McCallum 1994b), requiring large snags
to roost and nest in.
f. Distance to Water
No information located.
3. Landscape Factors
The flammulated owl occurs mostly in mid-level conifer forests that have a significant ponderosa
pine component (McCallum 1994b) between elevations of 366m (1200 feet) to 1676 m (5500
feet) in the north, and up to 2743 m (9000 feet) in the southern part of its range in California (Winter 1974).
b. Fragmentation and Patch Size
Owl territories are usually adjacent and about two square miles in size. The dispersing females move far enough to reach an adjacent territory (Reynolds and Linkart 1987b) however, forest fragmentation could negatively affect the dispersal of female owls if the amount of unsuitable habitat created exceeded the distance females are willing or able to travel to reach suitable habitat (Reynolds and Linkart 1987b). Reynolds and Linkart (1987) showed this distance to generally be about 425 m (1380 ft). A pair of owls appear to require about .8 to 4 ha (2 to 10 ac) during the breeding season, and substantial patches of brush and understory to help maintain prey bases (Marcot and Hill 1980). Areas with edge habitat and grassy openings up to 2 ha (5 ac) in size are benficial to the owls (Howle and Ritcey, 1987) for foraging.
c. Disturbance (Natural or Managed)
The owls have been shown to prefer late seral forests, and logging disturbance and the loss of
breeding habitat associated with it has a detrimental effect on the birds (USDA 1994). Timber
harvesting is often done in preferred flammulated owl habitat, and some of the species' habitat and
range may be declining as a result (Reynolds and Linkart 1987b, Bull et al. 1990). Several studies
have shown a decline in flammulated owl numbers following timber harvesting (Marshall 1957,
Howle and Ritcey 1987).
A main threat to the species is the loss of nesting cavities as this species cannot create its own nest
and relies on existing cavities. Management practices such as intensive forest management, forest
stand improvement, and the felling of snags and injured or diseased trees (potential nest sites) for
fire wood effectively remove most of the cavities suitable for nesting (Reynolds et al. 1989).
However, the owls will nest in stands that have been selectively logged, as long as they contain
residual trees (Reynolds et al. 1989). Flammulated owls successfully fledged young in a nestbox
placed in a thinned conifer plantation averaging sixty-five years in age (USDA 2001).
The suppression of wildfires has allowed many ponderosa pines to proceed to the more shade
resistant fir forest types, which is less suitable habitat for these species (Marshall 1957, Reynolds
et al. 1989). Encroachment of conifers along ridgetops can also negatively impact the black oak
component in the stand through competition of resources and shading resulting in loss of potential
nest cavities for flammulated owls in live hardwood trees. Roads and fuelbreaks are often placed
on ridgetops and the resultant removal of snags and oaks for hazard tree removal can result in the
loss of existing and recruitment nest trees.
Except for migration, this species is restricted to montane elevations with seasonally temperate
climates. Climate may influence the distribution of the species indirectly through the prey base,
(primarily nocturid moths) rather than directly through thermoregulatory abilities as this species
tends to forage at night when the temperatures are lowest for the day (McCallum 1994b).
4. Special Factors
a. Brood Parasitism
There is no documention of nest or brood parasitism from any avian species including the brown-
headed cowbird (USDA 1994).
Flammulated owls have a diet that consists almost entirely of insects. Reynolds and Linkart
(1987b) state that insects in the lepidopteran family (moths) are the most commonly taken
prey item, however, other studies claim beetles to be the most important (Marshall 1957). Prey
lengths vary from 6 to 55 mm (.2 to 2in), but most are at least 15 mm (.6 in) (Johnsgard 1988). McCalum (1994b) indicates that flammulated owls tend to be opportunistic insectivores and are not tied to the population cycles of a particular group of prey taxa, however, the early availability of noctuid moths, may advance the suitability of North American territories for foraging by up to one month, although this still needs to be researched. McCallum (1994b) also mentions that noctuid moths may be the only available food during cold spring nights as they have been observed flying over the forest canopy when temperatures were below freezing. Noctuids may be the only factor limiting flammulated owl migration, but they are probably limiting only in May and early June (McCallum 1994b). Speculation occurs as to what percentage of the diet of flammulated owls is comprised of small vertebrates, if any at all. Owls overwintering in northern areas subsist on vertebrates (McCalum 1994b), however further study is needed to assess what component vertebrates play in the owl's summer diet.
Failure to begin nesting in May and early June may require adults to molt while still feeding
their young in late summer. Though they may be able to tolerate such overlap, it would require an increase in foraging to meet the energy demands of the molt as well as the needs of the young. Owls have been known to starve during spring snowstorms (McCallum 1994b) possibly due to lack of aerial prey during extreme weather conditions.
5. Sensitivity to Human-Induced Disturbance
Flamulated owls are most susceptible to disturbance during the peak of their breeding season (June and July), which corresponds to the time when they are the most vocal. Clark (1988b) cautions against the extensive use of taped calls, stating that they can disrupt coutship behavior. McCallum (1994b) mentions that owls are tolerant of humans, nesting close to occupied areas and tolerating observation by flashlight at night while feeding young. Wildlife viewing, primarily bird watching and nature photography has the potential to disrupt species activity and increase their risk of exposure to predation especially during the nesting season (Knight and Gutzwiller 1995) when birds are most vocal and therefore easier to locate.
The effects of mechanical disturbance have not been assessed, but moderate disturbance may not have an adverse impact on the species. Whether a nesting pair would tolerate selective harvesting during the breeding season is not known, however, mechanical disturbance that flushes roosting birds may be a threat to adult survival in October when migrating accipiters may be more common than in June, when the possibility of lost reproduction is greater (McCallum 1994b).
Aerial spraying of carbaryl insecticides to reduce populations of forest insect pests may affect the abundance of non-target insects important in the early spring diets of flammulated owls (Reynolds et al. 1989). Although flamulated owls rarely take rodents as prey, they could be at risk, like other raptors, of secondary poisoning by anticoagulant rodenticides. Possible harmful doses could cause hemmorhaging upon the ingestion of anticoagulants such as Difenacoum, Bromadiolone, or Brodifacoum (Mendenhall and Pank 1980).
Predators include spotted and other larger owls, accipiters, long-tailed weasels (Zeiner et al. 1990), felids and bears (McCallum 1994b). Nest predation has also been documented by northern flying squirrel in the Pacific Northwest (McCallum 1994a).
As flammulated owls come late to breeding grounds, competitors may limit nest site availability (McCallum 1994b). Saw-whet owls, screech owls, and American kestrels compete for nesting sites, but flammulated owls probably have more severe competition with non-raptors, such as woodpeckers, other passerines, and squirrels for nest cavities (Zeiner et al. 1990, McCallum 1994b). Birds from the size of bluebirds upward are potential competitors. Owl nests containing bluebird eggs and flicker eggs suggest that flammulated owls evict some potential nest competitors (McCallum 1994b). Any management plan that supports pileated woodpecker and northern flicker populations will help maintain high numbers of cavities, thereby minimizing this competition (Zeiner et al. 1990).
Flammulated owls may compete with western screech-owls and American kestrels for prey (Zeiner et al. 1990) as both species have a high insect component in their diets. Common poorwills, nighthawks (Erhlich 1997), and bats may also compete for nocturnal insect prey especially in the early breeding season (April and May) when the diet of the owls is dominated by moths. (McCallum 1994b).
8. Exotic Species Invasion/Encroachment
Flicker cavities are often co-opted by European starlings, reducing the availability of nest cavities for both flickers and owls (McCallum 1994a). Africanized honey bees will nest in in tree cavities (Merrill and Visscher 1995) and may be a competitor where natural cavities are limiting, particulary in southern California where the bee has expanded its range north of Mexico.
9. Population Trend
So little is known about flammulated owl populations that even large scale changes in their abundance would probably go unnoticed (Winter 1974). Several studies have noted a decline in flammulated owl populations following timber harvesting (Marshall 1939, Howle and Ritcey 1987). However, more and more nest sightings occur each year, but this is most likely due to the increase in observation efforts.
Little data is available but a study by Reynolds and Linkart (1990) documented life spans up to seven years and one month for females and 8 years and 1 month for males.
11. Management Issues and Habitat/Population Objectives
a. Forest Harvest Rotations Vegetation Management
Logging practices that retain large trees for nesting cavities, provide an open structure, and retain islands of dense thickets and vegetation for roosting may not be as detrimental as a clearcut which may eliminate habitat components for at least 50 years (McCallum 1994b). Alterations in stand structure and canopy cover may increase or decrease predation from other raptors. Opening up of the canopy may increase use of the area by great horned owls for nesting and foraging. Accipiter nesting may decrease in the area due to loss of canopy but opening up the understory may increase foraging opportunities (McCallum 1994b).
b. Fuels Treatment
Based on studies on habitat, it appears the flammulated owl favors open forest structure for
foraging but dense foliage for roosting. Fire suppression leads to dense thickets of young stands
that provide roosting habitat, however, it may reduce suitable foraging habitat due to
inability to maneuver between trees. Grass and small shrubs, that harbor numerous prey species,
may be completely shaded out by the dense thickets which prevent sun from reaching the soil and
understory plants from growing. A comparative study of foraging performance and reproductive
success in dense thickets and artificially thinned stands of second growth would aid in identifying
any correlations of fire history and the current status of the owl. Fire suppression eventually leads
to wildfires, which can kill all trees, making large areas unsuitable for owls. Management practices that completely eliminate snags and/or densely packed small dbh trees for reducing fuel loads may also make an area unsuitable (McCallum 1994b).
c. Baseline Conservation Recommendations
1. Maintain multilayered open canopies with some shrub cover for foraging, along with adequate nest cavities McCallum 1994b). Preserve stands of mature trees .8 to 4 ha (2 to 10 acres) in size for nest stands (Marcot and Hill 1980).
2. Maintain snags with dbhs >50 cm (20 in) and taller than 6 m (20 ft) on ridgetops or upper slopes with east or south aspects, and in stands of large >50 cm (20 in) dbh trees with a high percentage of ponderosa pines in the overstory (Reynolds and Linkart 1987b, Bull et al. 1990).
3. Brush, understory, and even small grasslands should be maintained adjacent to the nest stands for foraging. Within the stand as well as in surrounding areas, a significant number of ponderosa pines and California black oaks with natural cavities or excavated by woodpeckers should remain undisturbed in the area to provide potential nesting habitat. Allow for future snag recruitment within and adjacent to the nest stand by continually retaining larger, mature trees (Marcot and Hill 1980, Bull et al. 1990). Management for pileated woodpeckers and northern flickers will insure future nest sites (Bull et al. 1990) will continue to occur within the forested stands.
4. The distribution and abundance of flammulated owls in California is not well known, therefore, more information needs to be obtained to begin to effectively manage for these small forest owls. Nocturnal surveys are needed to locate nesting localities, especially in broken coniferous woodlands with yellow pine and/or black oak and Douglas-fir (USDA 1994) and mist netting stations to identify migration corridors both to and from breeding grounds is needed.
5. Since flammulated owls will nest in boxes, it has been proposed that nest boxes be provided for them as a solution to the shortage of cavities. However, the costs of producing and maintaining the number and sizes needed by all secondary-nesting birds would be unreasonable. A better management alternative is to maintain existing cavity trees in management areas and provide long-term availability of large, diseased trees by setting aside areas with extended rotation periods within management units (Reynolds et al. 1989). Nestboxes can be used as a management tool to provide nesting habitat in areas where foraging habitat exists but natural cavities are lacking or absent due to past management activities or wildfire. They are not a substitute for natural habitat but serve as a temporary solution until natural habitat can become re-established in an area where it is already lacking.
Flammulated owls can be easily monitored by attracting them with taped and imitated calls. If
tapes are used, they should be played with caution, because these calling "intruders" can disrupt
the courtship behavior of some owls (Clark 1988b). Flammulated owl calls are ventriloquistic, making it difficult to locate a calling bird as it will sound farther away than it actually is (Reynolds 1987, Reynolds and Linkart 1998). The males regularly call within the home ranges, and respond well to taped recordings or imitation calls. Their vocalizations are distinctive and conspicuous. Using this method, it is possible to define territory sizes and densities (Marshall 1939). Caution should be used in determining habitat use by calls only, as males have been documented traveling up to 1 km to in response to a taped call (McCallum 1994b). Males call from spring arrival through the summer and after molt in fall (Phillips 1964). They are most responsive from May through early July (Reynolds 1987) but may vocalize most intensively for 2-3 weeks in spring (Bull et al. 1990). After eggs hatch, mated males cease to respond as readily, but unmated males respond through summer (Reynolds 1987). Since most of the calls heard in the field are from territorial reproductive males, nests can be located by systematic nest searches following audio detections. However, male presence is not adequate to determine habitat suitability as many males may remain unmated (Reynolds and Linkart 1987a, McCallum 1994a). The nests should be monitored so that success can be determined. Once territory boundaries were delineated, all suitable nesting cavities (tree cavities with entrance diameters >4 cm) within territories were located and checked for nesting owls (Linkart and Reynolds 1997).
Bull et al. (1990) studied the nesting ecology of flammulated owls by searching for calling males at night and finding their nests during the day. They walked routes that were 0.3-0.5 km (0.2-0.3 miles) apart and stopped every 0.3 km (0.2 miles) for 5 minutes. At each stop they first listened for owls, and if none were heard, they tried to illicit a response by imitating the owl's call. This method was effective, with 21 nests found in 1988, yet kept the disruption of owls to a minimum (Bull et al. 1990). The accuracy of some transect surveys have been questioned. Howle and Ritcey (1987) state that transect surveys may underestimate the actual number of birds present by up to 50%, due to complex soundscapes not allowing the birds to hear the callers. They recommend that the distance between call points be no greater than 0.5 km (0.3 miles). Flammulated owls respond best to tapes and imitated calls between a half hour after sunset and a half hour before sunrise (Reynolds and Linkart 1998).
Flammulated owls are not currently censused by the Breeding Bird Survey (USDI Fish and
Wildlife Service 1990). However, in 1999, the Breeding Bird Survey Protocol was successfully
tested on the Eldorado National Forest, California, to assess if it could be used to monitor
flammulated owls at night (USDA 1999).
Should nestboxes be used, a monitoring plan should be established to assess use, and to prevent
unwanted occupancy of non-native species such as the European starling and house sparrow.
Nestboxes should be checked prior to the arrival of flammulated owls for any required
maintenance as well as to document the first use by the owls. Visits should continue to record evidence of eggs, hatching, fledging and estimated time of banding the young and adult female. Failed nests should be revisited during the breeding season for any evidence of renesting (Marti 1997).
DeLong (2000) successfully captured migrating flammulated owls along a ridgetop in New Mexico by broadcasting flammulated owl calls at a netting station. He captured 94 flammulated owls during September and October with a capture rate of .3 birds per hour. Over 52% of the birds were captured during a five day span during a full moon. Three individuals were recaptured with an increase in weight suggesting the area around the netting station may have also served as a stop over during migration. The pilot study of the Sierra-Tahoe Owl Migration Project (STOMP) captured two flammulated owls the first night of operation in late August, of 2001, utilizing similar techniques along the Carson Mountain Range, along the eastern rim of Lake Tahoe in northern California (Smith 2001).
12. Associated Bird Species
The species depends on nothern flicker, pileated woodpecker, sapsuckers, and other primary cavity nesters to excavate nest cavities (McCallum 1994a). Loss of old forest types in the northern range of the species could eliminate habitat for the pileated woodpecker, resulting in loss of nesting cavities for the owl. South of the pileated woodpecker range, the northern flicker takes on the role as the main excavator of cavities utilized by flammulated owls (McCallum 1994b).
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