The Alarming Population Decline among Wild Birds, with Special Attention given to the Eurasian Skylark and the American Bobolink
I recall it was the summer of 1954 when my childhood hobby of collecting birds’ eggs and trading them at school came to an end. The British government implemented the Protection of Birds Act, 1954 forbidding the taking of wild bird’s eggs, and protecting the adults and their nests from human interference. This was with the intention, of course, of protecting endangered birds.
Up until that time, it was standard practice among country boys to go “bird nesting” and gather the eggs you found. The United States introduced similar protective legislation in 1918 through the Migratory Bird Treaty Act which applied to nearly 1100 species of bird, although American law did not cover non-native species such as the house sparrow, European starling and pigeon.
With such strict protections, you would have expected bird populations to boom, but this is not the case. The reasons are complicated and the points below are my efforts to describe some of the important aspects of avian demographics. The severity of the current decline on individual species of endangered birds is conveyed at the end of this paper using the skylark and the bobolink as examples.
A. Background data
- A recent survey of 529 bird species in the USA and Canada found a net decline of nearly 3 billion individual birds since 1970, with the current bird population 29 percent lower than it was. The impact is different by species and environment, but overall, the net population is down substantially. Common birds such as meadowlarks, dark-eyed juncos, horned larks and red-winged blackbirds are included in this impact, along with rarer bird species. There are also species that provide the contrary story. Bald eagles thrive today, with a gain of 15 million, falcon populations are up 33 percent, and there are 34 million more waterfowl (ducks and geese).
- Migrating birds are included in the overall decline. Current USA radar data suggests a 14 percent decrease in nocturnal spring-migrations among birds during the past decade.
- Europe is believed to be suffering a similar situation. In Britain, wintering waterfowl have more than doubled, plus species such as the jackdaw, wood pigeon, blackcap, great spotted woodpecker, nuthatch and mallard show a several-fold increase. Conversely, species like the song thrush, turtle dove, grey partridge, nightingale, cuckoo, swift, fieldfare and hawfinch depict alarming declines, making them endangered birds.
- There are 83 million pairs of breeding birds in the UK, down 19 million compared to the late 1960s, but the total population appears to have remained fairly constant since the 1990s. Not included in these numbers are the estimated 6 million captive red-legged partridges and 47 million pheasants that are released annually for shoots.
- A new study released by the University of New South Wales estimates the worldwide median number of wild birds as 50 billion, although it acknowledges uncertainty over the accuracy of these calculations. Reliable historic data does not exist because of the use of different methodologies in the past, and the difficulty of conducting global counts.
- Explanations for the cause of avian decline emphasize habitat loss (e.g. changing farm practices, urbanization), the use of pesticides, and climate change. By comparison, the global human population during the past 50 years has increased from 3.7 to 7.9 billion.
- Some species continue to be common and widespread, and four species qualify as members of the worldwide “billion birds” club; these are the house sparrow (with 1.6 billion birds), the European starling (1.3 billion), the ring-billed gull – named for the dark ring around its bill (1.2 billion), and the barn swallow (1.1 billion).
- Simultaneously, several bird species have become extinct. In North America, the dusky seaside sparrow, living on the east coast of Florida, was last seen alive during the 1980s, and the Bachman’s warbler that breeds in the south-east and mid-western states, and winters in Cuba, is suspected of falling extinct during the second half of the 1900s. Habitat destruction is the cause of both of these endangered birds.
- In Europe, the pied raven (a genetic color morph of the common raven), only found on the Faroe Islands, was last spotted during the 1940s. It possesses a large area of white feathering that was constantly reproduced, unlike albinism where white feathers are produced only for one generation. Since the year 1500, about 180 bird species worldwide have become extinct, out of the nearly 10,000 species that survive today.
- So why do these trends matter? The worry is what happens to nature when species that play key roles in decomposition, pollination and seed dispersal decline or disappear. The potential effects on human society as a result of plant extinctions, the loss of natural pest controls, and the spread of diseases are unclear.
B. The skylark and the bobolink
And now to the fate of the Eurasian skylark and the American bobolink (named for its bubbling “Bob O’Lincoln” song), both potentially endangered birds. The species are not related. The bobolink is a member of the blackbird family and the skylark belongs to the lark group of birds, with its cousin, the horned lark, the only lark that appears in North America. Both species rely on grassland and farmland for habitat. The American study found that the greatest loss in bird population during the past 50 years occurred among grassland birds, with a decline of 53 percent and a reduction of 520 million individuals.
Both of these species are countryside symbols of the return of spring and summer. Males deliver a bubbly, metallic song, often fluttering high above the fields, as they look for mates. Their melody is associated with joy, freedom and enthusiasm, and has inspired poets such as Emily Dickinson, Shelley, Tennyson and Wordsworth. Both species nest on the ground, but that is where the similarities end.
Their appearance is distinctively different as the illustrations show. The bobolink migrates annually from southern Canada and the northern states to southern South America, a return journey of approximately 12,500 miles (20,000 km). By contrast, skylarks in most of Europe do not migrate; also, the two species do not appear in each other’s territory, although efforts were made to introduce skylarks into North America, Australia and New Zealand during the late 1800s and early 1900s. Those released in North America were generally unsuccessful, although a few survive on the southern tip of Vancouver Island and at the higher elevations of the Hawaiian Islands. Introductions were much more self-sustaining in south-east Australia, Tasmania and New Zealand where the skylark has become well established, although its population is unknown. Both skylarks and bobolinks in their native territories are suffering severe declines, primarily because of habitat loss due to changed farming methods.
Skylarks, although relatively common and widespread in the UK, with a current population estimated at about 1.7 million, are considered to have suffered a population decline of around 75 percent since the early 1970s. The agricultural switch from spring to fall sown cereals has interfered with the birds’ food supplies and disrupted their nesting; the former spring sowing allowed skylarks to raise two or three broods of chicks each year, whereas winter cereals allow only one brood. Additionally, the move from hay to silage has caused nests to be destroyed by cutting machinery because of earlier harvesting, and on grasslands, intensified stock grazing has exposed nests to trampling and made them more accessible to predators. Efforts to reverse this trend are underway, including organic farming, offering incentives for sowing spring crops, and establishing rules to prevent nest destruction. Indications are that population numbers are at least stabilizing.
The plight of the bobolink, also an endangered species, is similar to the skylark, with its population declining around 65 percent since 1970. Even so, it is fairly common, with a breeding population of around eight million, of which 28 percent breed in Canada and 72 percent in the United States. Unlike the skylark, the bobolink produces just one brood each year. Habitat loss is the main cause for the reduction in its breeding territory. In its wintering locations, it has to put up with the use of dangerous pesticides and is often regarded as an agricultural pest. During migration, it is hunted and collected as food in Jamaica, and in Argentina it is trapped and sold as a pet.
Efforts are underway to reduce these interferences, with bans on the use of dangerous pesticides, encouraging grassland conservation on working farms, maintaining larger fields which are preferred by the bobolink, controlling natural prairie through prescribed burning, and probably, most important of all, incenting farmers to mow hayfields outside the breeding season. As with skylarks, we await the outcomes of these conservation efforts in an attempt to save these endangered birds.