Beaks, Bones and Bird Songs: How the Struggle for Survival Has Shaped Birds and Their Behavior - Roger Lederer (2016)
What We Do To Birds
When not protected by law, by popular favor or superstition, or by other special circumstances, [birds] yield very readily to the influences of civilization, and, though the first operations of the settler are favorable to the increase of many species, the great extension of rural and of mechanical industry is, in a variety of ways, destructive even to tribes not directly warred upon by man.
—GEORGE PERKINS MARSH, Man and Nature
Alexander Wilson, in his American Ornithology of 1840, described the Passenger Pigeon as living “in such prodigious numbers, as almost to surpass belief; and which has no parallel among any of the other feathered tribes on earth.” With a North American population of three to five billion birds, blackening the sky with its enormous flocks, the Passenger Pigeon was hunted with abandon. About 18,000 birds were killed every day by commercial harvesting in New York State in 1855. In a single year, a billion birds were killed in Michigan. The last bird died in a zoo in 1914. The Maoris hunted the flightless Moas of New Zealand to extinction by 1455. The last Dodo was seen in 1675, the species done in by hunting and the introduction of exotic animals to Mauritius. In the last century 100 birds have gone extinct, primarily by hunting and the introduction of predators (such as dogs, cats, rats, and snakes), and a few by habitat loss.
Imagine coming home one day and finding your house severely damaged, your bank accounts drained, and people you don’t know hanging around. It would be intimidating and stressful. You might be able to adjust, rebuild, and recoup your physical and financial losses, perhaps move elsewhere if you could find suitable lodging, or you could end up homeless, destitute, and starving. Scenarios like this happen after major disasters, but humans are resourceful and most of us manage to recover. Now imagine you are a forest bird arriving at your breeding grounds after a long flight. Instead of an expected stand of trees you find a few scattered saplings, shrubs, and flowers interspersed between newly constructed streets and houses. Bird species you are not familiar with have invaded your old haunts. Your normal food supply is nowhere to be seen. Could you survive?
Evolution is a superb sculptor. Over hundreds of millions of years the machinery of natural selection has honed birds to pinnacles of near perfection, having discarded tens of thousands of species along the way that could not meet the challenges of the ever-changing earth. Varying climates, shifting continents, volcanic eruptions, fires, and other perturbations effected changes in organisms, purging some and refining others. Sometimes these changes are subtle and take many generations, but given sufficient time, ecosystems recover and within them communities of birds suited for survival in their particular habitats. But since the beginning of the industrial revolution the physical environment began to change at a much faster pace, leaving many birds behind. Very few places have not been seriously disturbed by human activity. Cities like Beijing and New Delhi are virtually devoid of avian life, and in metropolises like New York and London, House Sparrows and Rock Doves dominate the avifauna.
Even New Zealand, often envisioned as a pristine land, has seen 40 of its 115 endemic birds go extinct and 41 introduced species become residents. Botanist Joseph Banks, sailing with Captain Cook to New Zealand in 1769, wrote: “This morn I was awakd by the singing of the birds ashore from whence we are distant not a quarter of a mile, the numbers of them were certainly very great.” New Zealand has lost more bird species than any other country and the majority of its land birds are threatened, endangered, or on the cusp of extinction. The only confirmed sighting in New Zealand of a Black-faced Monarch, common in eastern Australia, was in the late 1990s when it was caught by a cat, but it seems possible that the species once inhabited the islands. Every nation has some version of this problem. Some are addressing it by setting aside reserves, enacting environmental laws, and welcoming ecotourism, although many of those efforts are only moderate. Many other nations do little or nothing.
The Black-faced Monarch.
One interesting quirk in this dilemma is the Korean Demilitarized Zone (DMZ), which was created at the end of the Korean War in 1953 to minimize hostilities between North and South Korea. The DMZ is roughly 150 miles long and 2.5 miles wide. This strip of land has seen very little human activity and has become home to many species of plant and animals, including several thought to be extinct on the rest of the peninsula. The DMZ has become an important rest and refueling stop for birds on the Australasia-East Asia flyway such as the Red-crowned and White-naped Cranes and Siberian herons. This unusual example shows the resilience of natural communities if they are left to their own ecological devices.
Without the interference of humans, the natural extinction rate of birds is about one per century. Over the last five centuries approximately 200 species of birds have gone extinct and today at least 1200 are in danger of disappearing. By around 2050 we will begin to see about one bird species per year go extinct. The environment and the particular ecosystems in which birds evolved and to which they are superbly adapted for survival are simply changing too fast for evolution to keep pace. Based upon the historical rates of the evolution of 540 vertebrate species, animals would have to evolve at a rate 10,000 times faster than they do now to adapt to climate change by the end of the century. And climate change is happening at a slower rate than other perturbations—the disappearance of habitats is probably the most urgent problem.
THE PERILS OF HABITAT DESTRUCTION AND DEGRADATION
Habitat destruction and degradation are greater immediate threats to birds than any other predicament. Turning grasslands into cornfields or replacing a forest with condominiums eliminates the vast majority of the local birds. Traveling across the Sacramento Delta and the San Francisco Bay by train, I get a good view of the productive estuary and wetlands: rafts of ducks, cormorants on pilings, an occasional pelican flying by, and bunches of shorebirds which have wintered here for millennia. Oil and sugar refineries, megastores, a racetrack, all manner of unknown abandoned factories, and one enormous sea of asphalt, which evidently had some past purpose, interrupt my view. The placement of some of these operations may have some logic, but why an auto repair garage had to be built on the edge of valuable waterfowl habitat is beyond me.
European researchers reviewed thousands of bird surveys conducted from 1980 to 2009 in 25 European countries and scrutinized the population trends of 144 bird species. They found a reduction of a staggering 421 million birds over that time period—and 90 percent of that number was caused by a decrease in some of the most common species such as Eurasian Skylarks, House Sparrows, Grey Partridges, and European Starlings. Not all species waned in number: Great and Blue Tits, European Blackbirds and Robins, Chiffchaff, Blackcap, and even some rarer species such as Marsh Harriers, White Storks, and Stone Curlews increased, likely because of conservation efforts and stronger legal protection. But the increases were small compared to the overall loss of birds. Expanding urbanization and farming methods such as the increased use of agrochemicals and the loss of hedgerows contributed greatly to these losses.
The reduction in bird numbers is generally proportional to the loss of suitable habitat up to about a 50 percent decline. So a 30 percent loss of habitat, for example, results in an approximate 30 percent reduction in birds. But when the loss of habitat exceeds 50 percent, entire species diminish disproportionately and may vanish entirely. Habitat fragmentation, breaking a large expanse of habitat into smaller parcels, usually with loss of vegetation between the tracts, changes the dynamics and constitution of avian communities. As a habitat is broken up, the borders of the patches become longer compared to the enclosed inner areas. This edge effect engenders physical differences such as increased wind, sunlight, and differences in food types and abundance. But the results are not always predictable. A forest in central Sweden fragmented by logging showed a decrease in the number of arthropods on the forest edges, but a study in Canada reflected an increase in bugs. Some studies indicated an increase in bird species diversity on the edges and others a reduction. The outcome of habitat fragmentation depends on how the environment was split up, what bird species are present, and what the adjacent habitats are.
Studies in a tropical forest of Ecuador showed that a reduction in the size of forest patches generally resulted in a decreased number of bird species, but the consequences of habitat disturbance varied. With low levels of disturbance that put the forest back to a recent successional state, the diversity of bird species increased because an increase in open space and sunlight prompted more plant growth and productivity; with higher levels of disturbance that sent the forest back to an early successional stage, the diversity of bird species decreased because few plants were available to support the avian community. Not all avian guilds changed in the same way. Nectarivore species declined as nectar-producing plants declined; frugivores survived after some habitat disturbance as berry bushes increased in abundance; granivores multiplied as habitat disruption resulted in more grassy plant species; and insectivores responded positively, perhaps because of the decline in nectarivores which competed for insects. A survey in Mexico after a major hurricane in 1988 showed declines in nectar and fruit eaters (because all fruits and flowers were knocked to the ground) versus only minor reductions in the numbers of omnivores and insectivores. Wintering bird species suffered less than residents because the residents tend to be specialists and the visitors are adapted to be generalists on their wintering grounds.
Deforestation in New Zealand, leaving a large forest edge.
In the United States the composition of suburban bird communities depends largely on how the natural habitat was altered. In starkly urban areas with little natural habitat nearby, a few species such as House Sparrows and European Starlings appear in large numbers. Suburbs built in forested areas reduced the numbers of trees and birds, but when plans provided for stands of native vegetation, the diversity of bird species increased as the vegetation grew. In deserts or scrublands, suburban development and artificial watering meant a greater variety of plants and more birds. A study in Arcata, California, by Humboldt State University found that the total number of birds and diversity of the avian population diminished with increased road surface, while the abundance of non-native species increased.
Swainson’s Warblers of the southeastern United States have been adjusting to the disappearance of their preferred habitat of canebrakes and swamplands by establishing breeding populations in young pine plantations, which mimic to some degree the thick understory that the birds prefer. For seven to eight years the young pines, destined to become paper pulp, provide a suitable nesting habitat, but once the trees reach 40 feet succession removes the understory and the birds leave. About 60 million acres of pine plantations in various stages of growth are located in the southeastern United States, so some will always be available as nesting sites.
The birds that face the greatest challenges to survival are those with restricted habitats such as the Kirtland’s Warbler, which only nests in young Jack Pine stands in a small area of northern Michigan. Once near extinction 50 years ago, the bird population has been brought up to about 5000 birds today thanks to habitat restoration and their range is slowly expanding. The Bali Starling, once almost extirpated, numbered only six birds in 2001. Today about 50 birds live on Bali and another 60 or so on a small Indonesian island nearby where the bird was introduced. Many other threatened bird species occupy small islands. The Floreana Mockingbird, with only 200 individuals, is restricted to two tiny islets in the Galapagos. The Cerulean Paradise-flycatcher exists in a small population of perhaps 100 birds on the island of Sangihe, Indonesia. The islands don’t need to be oceanic ones; the Honduran Emerald (hummingbird) lives only in three isolated inland valleys of Honduras.
The take-home lesson is that the outcome of habitat disturbance on avian communities is extremely complex and every situation is unique. We do know, however, that minimizing habitat fragmentation, using environmentally sensitive practices such as the selective logging of trees, leaving edges of native vegetation around farm fields, and planting a variety of shrubbery and trees in suburbs and cities can help considerably in preserving diverse avian communities.
The Bali Starling has started on the road to potential recovery.
CLIMATE CHANGE: HOW BIRDS ADJUST, OR NOT
We know a good deal about the effects of climate change: rising air and ocean temperatures, coral reef bleaching, glacial ice melting, and sea level rising causing the inundation of islands. Lesser-known effects include large swaths of Rocky Mountain forest trees being killed by bark beetles, which now survive the milder winters. It is clear that bird habitats have been affected; the question is if and how birds will survive the effects of increasing temperatures.
A migratory journey initiated by the changing photoperiod has been an appropriate strategy for eons as a lengthening photoperiod in the Northern Hemisphere in the spring paralleled the increasing temperature. Although other factors such as soil moisture come into play, plants begin to leaf out, flower, and produce nectar and fruit as the soil and air warm. Insects and other invertebrates emerge and become active. But rising temperatures and the resultant earlier appearance of flowers and bugs are now causing an increasing disconnect between when the birds arrive and the availability of their food. These changes threaten both immediate and long-term survival of the species as spring is nesting season and abundant food is critical. Birds arriving after the peak of food abundance will face serious hardships, plants that depend upon birds as pollinators get little or no service, and herbivorous insects will have ample opportunities to eat whatever they wish until their aerial predators arrive.
Ten indicators of a warming world.
Birds with the longest migration routes or times in passage are at the greatest disadvantage and have suffered greater population declines than resident and short-term migrants. Populations of the European Pied Flycatcher, a black-and-white insectivore that winters in western Africa, have declined up to 90 percent in some locations. Its arrival time at the breeding grounds has not changed and is out of sync with its insect fare, which is emerging earlier. Although migratory behavior is genetically determined, it is malleable and some birds are adjusting. To reach their breeding grounds earlier, individual birds of migratory populations have the flexibility to winter not quite as far south as usual, leave their wintering grounds earlier in the spring, or fly faster to arrive at the nesting area earlier. The Icelandic Black Godwit population has moved the initiation of its northward migration up by two weeks. The birds did not change their spring migration arrival time; instead, they began their breeding cycle earlier than usual because of the warm weather, giving the young a chance to grow and migrate south (to the United Kingdom, Ireland, and France) earlier to find the best wintering areas. These offspring moved northward earlier the next season. So as the older population dies off, succeeding generations will be more in sync with warmer conditions. The American Bird Conservancy says that 20 species of migratory birds in North America arrived three weeks earlier in 2012 than they did in 1965. American Robins in Colorado are now arriving two weeks earlier than they did in 1995. Thirty years worth of data show that birds breeding in Oxfordshire, United Kingdom, have advanced both their arrival and departure times by eight days.
Many birds, including at least seven North American warbler species (Prothonotary, Blue-winged, Golden-winged, Black-throated Gray, Pine, Hooded, and Cape May), have shifted their range northward in the past 24 years by an average of more than 65 miles. The National Audubon Society reports that almost 60 percent of the commoner bird species in North America have relocated their ranges northward by an average of 35 miles and more than 60 species have moved more than 100 miles. The Baltimore Orioles may need a new name because by 2080 their feathered mascot will be nesting in Canada rather than Maryland. Minnesota might require a new state bird as the state is getting too warm for the Common Loon whose entire breeding range is moving to Canada. An exception, the Red-cockaded Woodpecker, has not moved, probably because its inflexible niche restricts it to the pine forests of the far southeastern United States. Thirty-five years of data from the North American Christmas Bird Counts by the Cornell Laboratory of Ornithology indicate that bird species need 30 years or more to shift their ranges in response to warming temperatures.
GLASS COLLISIONS, ALIEN PREDATORS, AND OTHER DILEMMAS
The problems of habitat loss and climate change are growing and seem intractable and perhaps insoluble, at least in the near term. But birds confront plenty of other anthropogenic problems that are significant, but can to some extent be mitigated.
Have you ever walked into a sliding glass door? Collisions with windows kill at least 100 million birds a year in the United States—more than any other direct cause besides habitat destruction—according to Daniel Klem, the leading expert in bird-window collisions. Not too long ago I received a call from an architectural firm in San Francisco. They were designing a building near the bay with numerous windows, a danger to both resident and migrant birds. Having recognized that problem, the San Francisco Planning Department had earlier established Standards for Bird-Safe Buildings (as New York, Toronto, and Chicago have done). The architects asked me to help them design a building to meet these standards, so I did a lot of research, including talking with Dr. Klem. Ultimately, public opposition to the building quashed the project.
Before 1900, most buildings were mainly brick, stone, wood. With new materials and designs, façades of buildings include a lot more glass. Birds usually cannot see the glass; they either look right through it or they see the reflection of vegetation in it and think there is safe passage. About half of the collisions with windows result in a fatality caused by brain hemorrhage or vertebral damage. We don’t know what happens in the long run to those birds that survive the impact and fly off. To reduce bird strikes, one can install screens, put decals or strips of tapes on the glass, hang ornaments in front of the glass, or place a thin film to make the glass opaque to birds. Taking advantage of the fact that birds can see UV, a German firm makes window glass with internal crisscrossing UV strips; birds can see the window but it looks normal to the human eye. Using “fritted” glass with imbedded patterns of lines or dots is another way to make windows more visible to birds. Windows can also be installed at an angle with the bottom of the glass further back than the top. This simultaneously minimizes the force of the impact as the bird doesn’t hit the glass straight on and the ledge formed at the bottom of the window provides a place for a stunned bird to recover.
Bird-window strikes can happen anywhere at any time, but most collisions are with large windows near ground level. Migration time is dangerous because birds are on the move, but so is wintertime for those birds that come to feeders. If you have a feeder, either place it within at least 3 feet of the house so the birds can’t pick up speed when they leave, or far away from the house so it’s not near any windows.
University of Toronto buildings with fritted glass to reduce bird strikes.
According to Dr. Klem, a number of rare birds are further imperiled by window collisions: the Swift Parrot of Australia, the Cerulean Warbler of North America (under consideration as an endangered species), the Black Rail of the southeastern United States and the Caribbean, the Kirtland’s Warbler of Michigan, and the Plain Pigeon of the West Indies. Unlike habitat destruction and climate change, individual and collective solutions exist for buildings and their windows. Birds have no survival skills to avoid windows without some help from us so implementing bird-safe solutions is imperative.
Cats and Other Alien Predators
The Egyptians domesticated house cats about 4000 years ago, revered them as sacred, and mummified them when they died (one cat cemetery in ancient Egypt contained 300,000 cats). Cats reached the Middle East and Europe about 1000 BC on the ships of Greek and Phoenician traders as the felines were kept on ships to control vermin. Roman armies carried cats with them to protect their grain supplies and when the armies retreated the cats remained in the United Kingdom and parts of Europe. House cats became common in the United States in the 19th century to keep agriculture-loving mice and rats under control.
An estimated 77 million domestic cats live in the United States today (maybe 600 million worldwide) along with an unknown number of feral felines. According to a U.K. study, the density of cats may be up to 665 per square mile, this number negatively correlating with the number of bird species. Only one-third of cat owners keep their cats exclusively indoors, so they hunt outdoors. In a U.S. study, small cameras attached to house cats that were free to roam indicated that they ate perhaps a billion birds each year. Add in feral cats and the number rises to 4 billion. Figures for the United Kingdom, Australia, and New Zealand are equally dismal. Perhaps 33 bird species worldwide have been exterminated by cats. The only positive side to this tale is that felines tend to take a decent proportion of less fit birds, many of which would not survive anyway.
This problem doesn’t have any easy solutions, but disposing of feral cats is a good start. My local city park was an unwanted pet dumping ground for years. On my walks I often spotted dozens of feral cats, especially adolescents, and noted that certain birds such as the California Quail had disappeared from the park, and birds of the lower vegetation such as towhees, thrushes, and robins were declining precipitously. At the same time cat aficionados were putting food out for the stray felines, no doubt increasing their numbers. Happily the volunteer organization Cat Coalition began trapping cats and finding homes for them. More than 1000 cats were removed from the park and after a few years quail and other birds reappeared.
Unfortunately, feral cats still roam my local park, as they do in many areas worldwide. There’s a story about the Stephen’s Island Wren, a flightless songbird endemic to the island of the same name near New Zealand. The birds were rare and the lighthouse keeper’s cat contributed to the bird’s extinction around 1900. About 1870, another New Zealand island, Little Barrier, was invaded by felines that went on to play a significant role in the total extinction of the Little Barrier Snipe, the local extinction of the North Island Saddleback, and the severe reduction in numbers of the Grey-faced, Cook’s, and Black Petrels. In 1905 New Zealand’s Canterbury Press had this quote: “And we certainly think that it would be as well if the Marine Department, in sending lighthouse keepers to isolated islands where interesting specimens of native birds are known or believed to exist, were to see that they are not allowed to take any cats with them, even if mouse-traps have to be furnished at the cost of the state.”
Little Barrier Snipe, painted in 1844, would be extinct by about 1870.
Cats are not the only alien invader to threaten birds. Dogs, goats, rats, snakes, opossums, and other predators have been major causes of extinction on oceanic islands. Virtually every native bird species such as the Cardinal Honeyeater and Guam Flycatcher was extirpated from the island of Guam by the brown tree snake, accidentally introduced with shipments of lumber from New Guinea just after World War II. Finding the island teeming with birds and lizards, the snakes advanced at a mile a year.
A study of 220 islands revealed that each successive predator introduction increased the number of endemic bird species lost. As endemic species declined and alien birds became more common, extinction rates fell. The more adaptable alien birds were apparently able to withstand pressure from predators. This is a lesson for those islands which still have endemic species not yet threatened by predators—do not let any more in.
Humans have created a number of other hazards that birds face on a regular basis all over the world. An unfortunate event occurred on New Year’s Eve in 2010 in Beebe, Arkansas. Thousands of Red-winged Blackbirds were roosting in a wooded area on the edge of town when, about 11:30 P.M., they came flying chaotically into town, frightened and disoriented, colliding with buildings, signs, cars, and each other; 2000–3000 birds died. Speculation as to the cause of death ranged from poisoning to a UFO invasion, but the most likely explanation is that they died of blunt force trauma or hypothermia or both. Huddled together for warmth for the night, the diurnal birds were driven by the noise of fireworks into the cold darkness and their demise. Similar mass bird deaths occurred in the week following that event; Turtle Doves died in Italy, Jackdaws in Sweden, geese and ducks in Ontario, and more Red-winged Blackbirds in Louisiana. It appears that all the birds were frightened by noisy celebratory activity and driven out of their roosts to their deaths.
I could write many more pages about problems such as light, noise, pollution, pesticides, power lines, communication towers, wind turbines, automobiles, airplanes, oil spills, fishing by-catch, hunting, poaching, egg-collecting, the pet trade, off-road vehicles, imported diseases, and lead ingestion, each of which contribute to the demise of birds. Enumerating bird deaths due to various causes is difficult and the numbers vary widely depending on the methodology used to collect data. Solar panels, for example, are estimated to kill 1000–28,000 birds a year and wind turbines 100,000–300,000. Coal may be responsible for eight million avian fatalities a year if the production and transportation of coal as well as its contribution to global warming are figured in. But, again, the two overwhelming causes for the reduction in bird populations are habitat destruction and climate change, followed by collisions with buildings and power lines, and predation by cats. We could dwell further on these awful tribulations, but let’s instead examine some of the ways that birds are adapting to the changing environment.
BIRDS ADAPTING TO A NEW WORLD
Urbanization—a shift from rural to urban areas—is perhaps the most difficult challenge to bird survival and may be a major driver of avian species extinction in this century. Only 2.7 percent of the earth is covered by cities yet the majority of the human population lives in them. The United Nations predicts that by 2050 more than half the population of the world will live in cities. In addition to habitat disruption and disappearance, the effect of urbanization is intense because of all it encompasses. Cities mean people, and the more people and their trappings, the fewer birds. During a weeklong visit to New York City, I saw few birds and virtually all of them were pigeons or House Sparrows. The two exceptions were in Central Park: a very cold Blue Jay on a fence and a soaring Red-tailed Hawk. Cities are a drastic change from native ecosystems.
Realizing that urbanization is spreading rapidly and changing habitats for birds, some ornithologists are shifting their research focus as well. Since 1970, the number of published research papers on urban birds and their habitats has more than quadrupled. The vast majority of studies have been conducted in North America and Europe; fewer than 5 percent were done in developing countries. Given that the population and thus urbanization of developing countries is happening at a far faster rate than in developed countries, the survival of birds faces major threats without the information needed to protect them.
But birds are not disappearing under asphalt and bricks without a fight. Many birds have adjusted to, and even benefit from, human activity. A good number have adapted to survive city life, particularly Rock Doves, House Sparrows, and European Starlings. In fact, more than 20 percent of the world’s bird species are represented in cities. Caracas, Venezuela, a city of six million people, has a non-native population of Blue and Gold Macaws surviving on what they can forage and what the locals leave out for them. Local legend has it that an Italian immigrant, Vittorio Poggi, rode around the city on his motorcycle with a macaw he trained to fly alongside; he eventually released 100 more birds which he bought, bred, or received from people who no longer wanted them as pets.
The Macaws of Caracas, Venezuela.
South London hosts several colonies of wild parrots, the most common being Rose-ringed Parakeets with perhaps 8200 pairs. Native to parts of Asia and Africa, Rose-ringed Parakeets were once kept by ancient Greeks and Romans and are popular as pets today. Their population has been on the rise at least since the 1990s, having escaped either from a broken shipping crate at Heathrow Airport or from the collapse of a large aviary, or having been released by the late musician Jimi Hendrix on Carnaby Street. The long, chilly winters no doubt cull the bird’s populations but they are surprisingly hardy, feeding on berries, seeds, nuts, buds, vegetables, and fruit. A bit aggressive, they tend to dominate bird feeders. Everyone seems to have adjusted to them and the U.K. Department of Environment, Food, and Rural Affairs (DEFRA) has deemed their elimination not cost effective. The story of the Monk Parakeet is different. Native to Brazil and Bolivia, they became established in London, probably because of escapees or releases from the pet trade. Their enormous communal stick nests, some as large as a small car, are often built on power transmission poles or towers and when wet sometimes cause blackouts or fires. Although the Monk Parakeet population is only about 150 birds, they pose such hazards that DEFRA has decided to reduce the population to 50 birds.
Parrots are common in other cities as well. In the center of San Jose, Costa Rica, amid buildings, shoppers, traffic, and general bustle, hundreds of Red-lored Parrots adorn building ledges and the trees of the central park. San Francisco is known for its flock of Red-masked Parakeets on Telegraph Hill, a bird colony that was generated, apparently, by a couple of escapees. The city of Bakersfield, California, hosts 1000 Rose-ringed Parakeets. Large flocks of Red-lored Parrots, Mitred Parakeets, and Lilac-crowned, Blue-fronted, White-fronted, and Yellow-headed Amazons can be found in urban locales of southern California where they live off the fruits and nuts of plants, exotic imports like the birds themselves. Non-native parrots of three dozen species have found refuge in North America, including the very adaptable Monk Parakeets of Brooklyn, Chicago, and Montreal.
A potential threat to crops, the Monk Parakeet population is increasing rapidly in the United States and its large nests have interfered with electrical transmission lines.
Overall, urban bird populations average 30 percent higher than nearby rural populations of the same species. Feral pigeons and House Sparrows have been associated with humans for thousands of years so it’s not too surprising that the populations of these birds are higher in urban habitats as compared to nearby rural areas. But even European Blackbirds, which invaded cities less than two hundred years ago, have urban populations two orders of magnitude higher than adjacent woodlands, their native habitat. Since the 1950s, 47 bird species living in the inner city of Warsaw, Poland, have diminished in number or disappeared as the city grew, but the populations of 37 species increased and 12 new bird species colonized the city.
About 114 bird species utilize cities or suburbs worldwide for part or all of their lifespan. Although domestic predators (dogs and cats) are common, predation pressure is low because dogs and cats also have human food to rely on and birds have an infinite number of hiding places. Gulls, vultures, ravens, and crows hang out at garbage dumps and along roadways looking for the superabundant food scraps. Hummingbirds, towhees, chickadees, nuthatches, sparrows, doves, finches, jays, and woodpeckers frequent bird feeders. Falcons, hawks, and owls even nest in cities, where they can find abundant prey. George and Gracie, a Peregrine Falcon pair, have been nesting on a San Francisco building since 2005; in 2014 they nested in a 30th-floor planter on a financial district skyscraper. A famous Red-tailed Hawk in New York City, dubbed Pale Male because of his light-colored head, has nested on an apartment building overhang on Fifth Avenue for 24 years with a new female about every three years. That he has survived that long is amazing as 75 percent of Red-tailed Hawks die before their first birthday.
The populations of year-round city resident birds have held steady or showed a strong increase since the mid-1970s. However, migratory birds that only use urban areas for nesting, such as Common Nighthawks and Chimney Swifts, are declining because competition for food and nesting sites with the growing populations of sedentary urban birds is too great for them. As cities grow, fewer and fewer niches remain for birds that only visit for a few months of the year.
New Reactions to City Predators
Another indication that birds are adapting to urban environments is their reaction to city-living predators. An analysis of the response of 44 European bird species to an approaching human showed that urban birds flew shorter distances to escape threats than rural birds of the same species. The longer the bird species were associated with the city (as judged by the number of generations) and the larger their populations, the shorter the escape distances, indicating the birds are adapting to city life. Urban birds with shorter flight distances are also less susceptible to predation by the European Sparrowhawk (and presumably other predators). However, as the prey population increased, so did the success of the sparrowhawks as they honed their urban hunting skills.
Besides cats, mammalian predators in urban and suburban areas include raccoons, opossums, foxes, dogs, rats, and skunks. Birds have few survival tactics except mobbing or escape to cope with predators, but researchers in Europe say that might be changing. They captured 1132 birds of 15 species in rural and urban areas, grading every bird on its escape behavior when in a human hand—squirming, biting, alarm calls, and feather loss. Researchers also timed how long each bird remained immobile “playing possum”—when laid flat in a human’s open palm. Urban birds shed more feathers, let out more calls and screams, and flew from the hand faster than country birds did. It appears that these tactics are escape techniques modified to cope with city predators, especially cats.
Plumage Color Changes
Originally from Asia, the highly invasive Morrow’s Honeysuckle has become common in the suburbs of the northeastern United States. Cedar Waxwings are frugivorous birds with yellow-tipped tail feathers. After about 1950, birds were being found with orange-colored feather tips, a result of the birds ingesting honeysuckle berries with the red-purple pigment rhodoxanthin. Whether this color change has any social or sexual implications for the birds is not known. In central Ohio, the brightness of male Northern Cardinals’ red plumage decreased as urbanization and exotic honeysuckle plants increased. The brighter red males from rural or forested areas with little or no honeysuckle bred earlier and raised more offspring than their dull city dweller cousins.
In Europe, the favorite food of the Great Tit is caterpillars, which live on a diet of carotenoid-containing leaves. Carotenoids are important as precursor vitamins, antioxidants, and pigments in birds, responsible for the Great Tit’s yellow chest and abdomen. Urban-dwelling caterpillars are less abundant, find fewer leaves, and contain lower amounts of carotenoids, so parent Great Tits have to make more foraging trips to feed their young caterpillars than forest-inhabiting nesters. In a polluted area, the carotenoid levels of the insects are so low that the young birds leave the nest with a dull yellow chest rather than a bright one. Whether these changes in feather color will alter social interactions among the birds is yet to be seen.
Researchers in Paris discovered that darker city (feral) pigeons are healthier than lighter ones, partly because darker birds can rid their bodies of heavy metals. Wild birds kept in cages for a year had their flight feathers tested for heavy metals such as zinc, cadmium, copper, and lead. Eumelanin, the pigment responsible for the black-brown dark-colored feathers, binds to heavy metals. At the next molt the new feathers were tested for heavy metals; the levels were down by 75 percent. Some evidence shows that darker pigeons are increasing as a proportion of the population, because their survival rates are higher and reproduction more successful. Like many evolutionary changes the darker birds just happened to have a physiology that benefited them when they inhabit an urban area with heavy metals.
Nesting and Foraging Modifications
The Barn Swallow has been associated with human environments in Europe for more than 4000 years and today over 99 percent of Barn Swallows nest indoors in barns, sheds, or other buildings. Given a generation time (average time between two consecutive generations) of Barn Swallows of 1.59 years, about 2500 generations allowed plenty of time to adapt to nesting in warmer, safer, human-constructed places. Chimney Swifts are so accustomed to nesting in human-made structures that only 10 instances of the bird nesting in the wild in the last century are known. The European Blackbird has only been nesting in close proximity to humans for about a hundred years. With a generation time of 2.27 years, they have only had 44 generations to adapt, so only 15 percent of blackbirds nest indoors. But city-dwelling blackbirds nest a few weeks earlier than their rural relatives and have two or three broods compared to the single brood of those nesting in forests; there have even been instances of winter broods among city blackbirds. The increased amount of light, providing more time for foraging and inducing the birds to breed earlier in the season, amelioration of weather conditions, and both natural and human food sources apparently make life a bit easier for these urban blackbirds.
Some wild bird species incorporate aromatic plants into their nests to repel parasites. House Sparrows and House Finches in Mexico City put fibers from filter cigarette butts into their nests. Nicotine is a known arthropod repellent and the cellulose acetate in the filters contains significant amounts of the chemical. The more cellulose acetate in the nest the fewer the mites infest it. The cellulose acetate may simply be available nesting material for the birds, but the birds are benefitting from its parasite-repellent qualities. Although this study was done in 2013, there have been reports of birds incorporating cigarette filters into their nests for at least 45 years. One downside of this behavior is reflected in the incident of a building fire in South London, caused by a bird carrying a lit cigarette butt into its nest in a hole in the roof of the building. Several other reports from fire departments indicate that birds such as House Sparrows, European Starlings, and Rock Doves have been implicated in starting structural fires.
House Finch nest.
Birds learn the characteristics of their city with its litter, garbage, and intentional feeding providing ample opportunity for foraging. House Sparrows and starlings frequent outdoor cafes, pigeons extend their feeding bouts by foraging under streetlights at night, and many species quickly learn the location of bird feeders. In 1994 the month of February was designated as the official bird-feeding month in the United States. Over 60 million Americans feed birds at various kinds of feeders, spending over four billion dollars annually for food and feeders. Dozens of different species and billions of birds partake in these backyard offers. Bird feeding has been a regular pastime for at least a century and a half and probably far longer.
Adapting to Traffic
A 2013 paper reported on a 30-year study of Cliff Swallows killed by vehicles in Nebraska. Colonies nesting on bridges and overpasses flew over highways and passing traffic killed the birds. In the 1980s the kills averaged 20 birds per year, but since 2010 the annual average had dropped to five birds even though the colony had doubled in size and vehicular traffic stayed steady. Researchers Charles and Mary Brown wondered what was happening, so they took measurements of the deceased birds and compared them to live birds in the colony. The live birds had a 4.2-inch-long wing while the wings of the road-killed birds were 4.5 inches long. Studies of swallow flights indicate that shorter wings are better for making quick turns and make the birds better at dodging traffic; “natural” selection (by vehicles) is weeding out the longer-winged birds.
Evening Grosbeak at feeder.
Researchers in France measured the distance from moving vehicles at which birds began flying to avoid being hit. One would think that the faster the vehicle is traveling, the greater the distance at which the bird would initiate flight. Actually, the birds responded not to the speed of the vehicle, but to the posted speed limit! It appears that birds that regularly inhabit a stretch of roadway have learned the most common speed, which is somewhere around the posted limit, and react as if the vehicle was traveling at that pace, even if it were dawdling or speeding. Since most cars travel around the posted limit, this appears to be the best strategy to avoid collisions with oncoming traffic.
Noise and Bright Lights
Songbirds convey information to mates and competitors through song, but as environments get noisier, communication becomes more difficult. Long-term survival dictates some adjustment. Because most city noise (traffic, lawn mowers, industry) happens at low frequencies and the bird songs overlap some of those frequencies, it is advantageous for the singers to emphasize higher frequency song notes and dampen their low frequency notes. Male Song Sparrows in Portland, Oregon, sing higher-frequency notes and reduce the loudness of their low notes in noisy city environments. European Blackbirds in Salamanca, Spain, act similarly—more ambient noise causes birds to increase the pitch of their song. In the city with a noise level of 66 decibels, the average maximum frequency of bird songs was 3165 Hz while in the rural surrounding rural area where noise levels averaged only 37 decibels the song frequency was 2657 Hz. Comparable effects have been observed in Great Tits and Common Nightingales. Is this an evolutionary adjustment or just an acclimation by individual birds? Two populations of the Reed Warbler, widespread across Europe, were studied. One population resided in an area that was noisy for much of the year; the other lived in a much quieter locale. In the noisy environment, the Reed Warblers sang higher frequency songs than the birds in the quiet location. But when the noise levels were similar, so were the song frequencies. This indicates flexibility in their song repertoire, not necessarily an evolutionary change. But in most songbirds, a significant learning component by young birds occurs about a year after fledging. So it could very well be that young birds in noisy environments will only learn the higher ranges of their species’ songs and pass this knowledge onto their offspring. Being able to communicate one’s song is necessary to survival, so shifts in genetic makeup are likely to occur. Birds like the Rufous-crowned Sparrow simply decline or disappear with urbanization, so their songs remain unaffected in wild populations.
Since the arrival of the first commercially successful light bulb in 1879, the night sky has increased in brightness by a factor of six thousand. Scientists in Vienna found that in areas with streetlights, some species of birds begin to sing earlier than they do under normal lighting. In a seven-year study of the reproductive behavior of Blue Tits in the United Kingdom, female birds in nests on the forest edge near streetlights began to lay eggs an average of 1.5 days earlier than those in darker areas. Males in lighted areas were twice as successful in mating with a female in addition to his mate. It seems that the additional light gave the females more time to prepare the nest and start laying eggs and the males had additional time to sing and attract females from a different territory. Studies in Leipzig, Germany, found that the European Blackbird is healthier in cities than in the wild because the near-constant light of the city allows it to forage a lot longer.
Rufous-crowned Sparrow singing.
Adapting to urban environments apparently means adopting a sedentary lifestyle. The European Blackbird was formerly a migratory bird that preferred forests, but over the last several decades it has become a common city bird. Researchers compared fourteen populations of blackbirds, seven urban and seven rural, across a broad swath of northern Europe and found a strong trend for the urban populations to be more sedentary than rural ones. The tendency was strongest in the more northerly populations of Latvia and Estonia, even though the colonization by blackbirds in those countries was rather recent, occurring somewhere between 1930 and 1950, indicating a fairly rapid evolution of sedentary behavior. But a number of migratory bird species continue to nest in cities, such as the Pied Wagtail, Willow Warbler, and Song Thrush of Europe, and the American Robin and Cliff Swallow of North America.
Various urban features, too many to expound on here, affect migratory birds, but a particularly interesting one is all the electronic emanation from cell phones, radios, TV towers, and satellites—a common feature of cities. We don’t know much about how birds are affected by all this but one study by a German researcher, Henrik Mouritsen, who moved his laboratory from a rural area to the city of Oldenburg, gives us some indication. After moving, he found that the European Robins he was investigating no longer oriented in the proper direction in their wooden cages. After three years he discovered the cause was electronic interference from the outside. It wasn’t mobile phones, power lines, or wireless signals, but AM frequencies, those used by radio stations and certain kinds of electronic equipment. When he used aluminum-screened cages and grounded them electrically, the birds oriented normally. AM frequencies are stronger and reach farther at night, which may affect the birds’ navigational abilities. The study shows us that there are all kinds of electronic signals in our urban world and we have much to learn about how they affect the lives of birds and whether they are adapting to them in some way.
PEOPLE HELPING BIRDS SURVIVE
Birds cannot survive in the long run without assistance from us in the form of various organizations dedicated to birds. In the mid-18th century, Marie Antoinette was a fashion trendsetter, which eventually led to her downfall from the French throne. By wearing feathers in her hat she initiated a demand for feathers that by the 1850s was in full swing with hundreds of thousands of birds being killed for their plumes, especially egrets. In the United Kingdom at that time, the price of feathers by weight was equal to that of gold. Songbirds and even entire Arctic Terns were mounted on hats and sizeable colonies of birds were decimated in the process. Just as egret colonies teetered on the brink of extinction, the Lacey Act, prohibiting the interstate commerce of wildlife, was enacted in the United States in 1900, ending the bulk of the commercial plume trade.
The National Audubon Society of the United States came into being to stop the slaughter of wild birds and today is involved in many major protection efforts across the country. The Royal Society for the Protection of Birds was formed in the United Kingdom to counter the feather trade in the Victorian era and today focuses on conserving and protecting natural habitats. BirdLife International is the world’s largest nature conservation coalition, with 120 partners across the world who manage 1553 reserves or protected areas covering 11.1 million acres.
Numerous programs are aimed at teaching people to appreciate birds, value the natural world, and support efforts to protect and preserve its inhabitants. The Celebration of Urban Birds, the Urban Bird Sounds Project, Neighborhood Nestwatch, the Fledgling Birder’s Institute, the Birding Challenge, National Wildlife Federation Schoolyard (and Backyard) Habitats, and the Shorebird Sister Schools Program are just a few. The International Migratory Bird Day highlights and celebrates the migration of nearly 350 species of migratory birds between nesting habitats in North America and their wintering grounds. The Bird Education Alliance for Conservation is a coalition of educators representing universities, bird observatories, local, state, and federal agencies, and environmental education and conservation groups. Partners in Flight is a cooperative among federal, state, and local governments, charities, professional organization, conservation groups, industry, and others to seek ways to protect migratory land birds. And the list happily continues.
Birdwatchers: The Ultimate Key to Survival
Birdwatching is the fastest growing outdoor activity; somewhere between 45 and 85 million people call themselves birdwatchers and invest $20–$35 billion each year in birding activities. The average birdwatcher has an above average income and spends $1500–$2000 a year on books, binoculars, telescopes, travel, and lodging. Serious birders might spend close to $5000 for an exotic birding trip led by one of 127 bird-guiding companies. Neil Hayward, from Cambridge, United Kingdom, sighted 750 species in North America in 2013. He spent 195 nights away from home, drove 51,758 miles, was at sea for 147 hours, and took 177 flights through 56 airports while on his quest.
The Blue Jay is a bird most people are familiar with and no doubt is responsible for getting people interested in nature and conservation.
More and more bird festivals are offered each year, and big days and big years are organized all the time. January 5 is National Bird Day. It’s a big sport, but not just an esoteric one; birdwatching is becoming more ingrained into our national consciousness. But most birdwatchers don’t participate in festivals or competitions, they just want to incorporate birdwatching into their everyday strolls.
Too often there is a disconnect between the natural world of birds and other organisms and our technology-obsessed everyday life. Birdwatching connects people to the environment and helps them understand why birds need protection from human activities. And the more we understand birds, the more we understand the environment from which they come and which they depend upon for survival, and the more likely we are to be able to protect them.
Birdwatchers play a key role in helping birds survive.
Until the early 20th century, birds were being slaughtered for food, feathers, eggs, and sport. The Passenger Pigeon, Labrador Duck, and Great Auk did not survive this onslaught, but herons, egrets, and songbirds did thanks to the efforts of some enlightened politicians and activist citizen groups. From the role of protecting birds, the mission of protecting ecosystems arose slowly but necessarily. Are these efforts and laws sufficient to ensure the survival of birds? I am cautiously optimistic. The individuals, agencies, and industries that have created the greatest challenges to the survival of birds—habitat destruction and climate change—tend to be shortsighted and have goals at odds with bird conservation. On the other hand, the powerful plumage trade, the egg and meat hunters, and overhunting in the name of sport have largely been halted, so change is possible. Political action is necessary, but education is primary. Birds have evolved superb adaptations to the natural world and evolution polished those adaptations as the world changed. But now that we humans have put environmental change in high gear, birds can no longer keep up, so we need to be partners in their survival.