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Rachel Carson’s ‘Silent Spring’ 60 years on: Birds still fading from the skies

The spotted tody-flycatcher, native to South America and the Caribbean, hunts insects alone or in pairs, and is well-adapted to humans, happy in forest or overgrown pasture. Image courtesy of Alexander Lees.

The spotted tody-flycatcher, native to South America and the Caribbean, hunts insects alone or in pairs, and is well-adapted to humans, happy in forest or overgrown pasture. Image courtesy of Alexander Lees.

  • Rachel Carson’s “Silent Spring” catalyzed the modern environmental movement and sparked a ban on DDT in the U.S. and most other nations, though DDT has since been replaced by a growing number of other harmful biocides.
  • Now, 60 years later, birds may face more threats than any other animal group because they live in — or migrate through — every habitat on Earth. Birds are impacted by land-use changes, pollution (ranging from pesticides to plastics), climate change, invasive species, diseases, hunting, the wildlife trade, and more.
  • The 2022 update to the “State of the World’s Birds” report notes winners and losers amid increasing human alteration of the planet, but documents a continuing downward trend.

In her landmark 1962 book, Silent Spring, biologist Rachel Carson chronicled the damage — and looming consequences — of human “contamination of air, earth, rivers, and sea with dangerous and even lethal materials,” which she called “elixirs of death.” In the book’s spellbinding opening parable, which profiles a fictional town of the future, she wrote:

“It was a spring without voices. On the mornings that had once throbbed with the dawn chorus of robins, catbirds, doves, jays, wrens, and scores of other bird voices there was now no sound; only silence lay over the fields and woods and marsh.”

Silent Spring focused on DDT. During World War II, the U.S. military declared this revolutionary biocide to be “the most powerful of the new weapons the army is now using in its war on insect-borne diseases,” specifically malaria, yellow fever, typhus and bubonic plague.

After the war, planes “broadcast sprayed” leftover stockpiles across the United States and many other countries to kill weeds, crop-eating insects and to control mosquitoes.

DDT was hailed as a miracle biocide and was produced and marketed for years with virtually no environmental testing. Its toxic bioaccumulation proved to be a disaster for birds, leading to the biocide’s being banned. Image courtesy of the Science History Institute.

DDT was the world’s first modern synthetic insecticide, a chlorinated hydrocarbon that lingers in the environment. It was never safety-tested. Later studies determined that it causes neurological damage, is toxic to wildlife and humans, stores in fatty tissues, and bioaccumulates in greater and greater concentrations up the food chain.

DDT sparked a global avian catastrophe. It leached into soil and water, contaminating the rodents, worms, insects, fish and other prey that birds fed on, killing some outright. The biocide also interfered with calcium metabolism in egg production, particularly in birds of prey, which were “catastrophically impacted,” says Alexander Lees, a conservation biologist at Manchester Metropolitan University and an associate of the Cornell Lab of Ornithology.

Thin-shelled, fragile eggs fractured in bird nests, unable to support the weight of a growing embryo. Incapable of reproducing, just 417 bald eagles remained in the lower 48 U.S. states by 1963. The California condor was extinct in the wild by 1987; just 27 were left alive in captivity. Peregrine falcons went missing from parts of North America. Scores of songbirds vanished, too, as did cormorants, pelicans and other waterbirds.

The gray crowned crane has two endangered subspecies in African wetlands, savannas, farms and ranchlands, and is declining. The cranes are threatened by everything from habitat loss, drought and pesticide use to hunting and egg collecting. Image courtesy of Alexander Lees.

Carson’s legacy: Bird species recoveries since DDT

Birds are beloved by many, and Silent Spring became a bestseller despite brutal industry attacks. Critics called Carson’s claims “more poisonous than the chemicals she condemns” and labeled her “an alarmist, mystic and hysterical woman.” As the 20th century’s most influential environmental book, it catalyzed the modern environmental movement, and sparked creation of the U.S. Environmental Protection Agency (EPA) and passage of the Clean Air  and Clean Water Acts.

Sixty years have passed since Silent Spring hit the shelves; 50 since the EPA outlawed DDT; and 20 years since most nations banned it and other persistent organic pollutants under the Stockholm Convention. The result: Many of the birds most threatened by DDT made miraculous comebacks.

Peregrine falcons now nest on every bridge spanning New York’s Hudson River. More than 300,000 bald eagles fill U.S. skies. They, along with brown pelicans and ospreys have been removed from the U.S. endangered species list. More than 300 California condors fly wild, and as of this month, they soar over northern redwood forests for the first time in a century.

A range of environmental regulations and protections have brought back both individual species and entire bird groups. However, these are the exceptions amid a broader downward spiral that began centuries before Carson’s book or the advent of synthetic chemical biocides.

Since birds inhabit every ecosystem, they’re affected by every environmental disturbance: lost habitat, climate change, pesticides, pollution of air, water and land, invasive species, and disease. A 2022 update to BirdLife International’s “State of the World’s Birds” reports what co-author Tris Allinson called “a steady ongoing, inexorable decline.”

But “conservation works,” says Brian Rutledge, former vice president of the National Audubon Society: With good science and sufficient investment, it’s possible to reverse the declines.

‘Ongoing declines’

With some 11,000 known avian species worldwide, birds are ubiquitous. They’re present from pole to pole, from high mountains and deserts to remote islands and cities. They play integral roles in every biome, pollinating plants and spreading seeds, including fruit- and berry-bearing varieties that feed many animals. Each year, they consume 400 million to 500 million metric tons of insects that can damage crops and kill trees. A single bird can eat enough bugs to save 29 kilograms (65 pounds) of coffee on a Latin American plantations.

And people love birds: In the U.S. alone, the bird-watching industry is valued at $41 billion per year.

Birds are also important indicators of the state of the planet — and they’re in trouble. Since Carson’s time, numbers have dropped by “many billions,” says Allinson, a senior global science officer at BirdLife International. Nearly half of all species (5,245) are declining. Anyone alive in 1970 in the U.S. or Canada has seen one in four birds disappear during their lifetime, 2.9 billion in all: from robins and sparrows, to blackbirds, finches and other familiar backyard denizens.

Birds are getting hit from all sides: In the Anthropocene, humans are altering the natural world to an “unparalleled degree,” disrupting and devastating ecosystems and driving extinctions. It’s impossible to gauge how many species have vanished globally since the passing of the dodo in 1681 — the first recognized bird extinction.

The best guess comes from the Red List of Threatened Species. This database, maintained by the International Union for Conservation of Nature, tracks wildlife population trends. The list has recorded 159 bird extinctions dating back to 1500 C.E., when the European Age of Discovery began impacting the world. An additional five species only exist in captivity; 22 more are “possibly extinct.” Most of those are flightless or island species.

American black vultures in Maranhão, Brazil. Scavengers can die from eating poisoned carrion. Image courtesy of Alexander Lees.

The trajectory is of “really significant global concern” for about one-fifth of all birds, says Allinson. “Each year, when we reassess [for the ‘State of the World’s Birds’ report], we find slightly more species that are falling. It’s unfortunately often a one-way process.”

But that’s not the whole story. With focused conservation, “we’ve reversed the declines in some rare species,” notes Lees. The 2022 status report, of which he is the lead author, tallied 676 rebounds (6% of all species); another 4,300 (39%) are holding steady.

Many waterbirds, for example, are increasing in North America and Europe. Common cranes and Eurasian spoonbills, once eaten at medieval banquets and gone from Great Britain for centuries, are now breeding on the edges of major cities. Flamingos still mass in such numbers that the landscape turns pink. Massive flocks of starlings — though considered invasive pests in the U.S. — still whirl and shapeshift in a synchronized dance through the sky in almost mystical murmurations.

Flamingo in Río Lagartos Biosphere Reserve, Yucatan Peninsula, Mexico, where these birds nest in the tens of thousands. Image © Steve Winter.

The threats birds face

The growing avian crisis, like the larger extinction crisis, is driven by increasing human population, overexploitation and overconsumption, says Lucy Haskell, science officer at BirdLife International. Even the “winners” — birds that have bounced back from the brink — still face myriad, multiple, compounding threats.

Avian species collide with power lines and smash into lit-up buildings during nighttime migrations. They’re poisoned when they eat animals shot with lead-based bullets. They ingest plastic. Indian vultures were nearly exterminated by eating carrion from livestock that were treated with a veterinary drug. Rutledge calls poorly sited 120-meter (400-foot) wind turbines “bird Cuisinarts,” and is amazed that safer technology hasn’t hit the market. Domestic cats kill billions of birds each year.

But deforestation is by far the greatest exterminator. Lees calls habitat loss, fragmentation and degradation “the three horsemen of the apocalypse.” Birds are losing space to breed, nest, roost and find food, often left with only tiny, unsuitable scraps of habitat.

Nearly two-thirds of all birds inhabit forests, and “many can’t live anywhere else,” says Haskell. That’s particularly true in the tropics, which lost primary rainforests last year at a rate of 10 soccer fields a minute. Annual deforestation in the Brazilian Amazon has hit a 10-year high. Globally, more than 252,000 square kilometers (97,500 square miles) of tree cover vanished from August 2020 to July 2021, an area the size of the U.S. state of Wyoming.

Meanwhile, monoculture reforestation efforts nurture relatively few bird species, and prove inhospitable for specialists like the white-backed woodpecker that needs dead trees for nesting. Boreal forests are being logged for lumber, for toilet paper sold to the U.S., and are falling to harvest the sand beneath them — used to frack natural gas wells and oil wells. Old-growth forests in Canada and native forests in the U.S. are being leveled to produce wood pellet biofuel — a “green energy” climate solution that may emit as much or more carbon as coal.

Land used for agriculture increased sixfold over the past 300 years and now affects more than 1,000 globally threatened avian species, says Haskell. The greatest destruction is in the tropics, driven by commodities: timber, paper, palm oil, soy, sugar, beef and others, produced at industrial scale.

“The fundamental question,” Lees says, “is how we can we feed X billion people, without destroying the planet.”

High- or medium-impact threats affecting five globally threatened bird species and the underlying drivers of these threats. Data from BirdLife International. Image courtesy of Lees et al. (2022).
Rainforest being burned in Aceh, Sumatra, to make way for oil palm plantations. Image © Steve Winter.

Changing climate, severe weather, disease

One of the biggest changes since Rachael Carson’s time is increasing damage from human-caused climate change, which didn’t get public or government attention until 1988. It now ranks as the second-greatest threat to birds. The effects on wildlife and ecosystems are only beginning to unfold. But “100-year” floods and storms are now common and extreme drought and unprecedented wildfires are scorching Earth with growing regularity.

We do know that rising temperatures are altering birds’ seasonal rhythms. To successfully raise chicks, timing is everything. Spring migration, breeding and nesting need to be synchronized with peak food abundance. But individual adaptations by plants, insects and animals are uncoupling well-timed systems finely tuned over millennia. It’s an asynchronous cascade that may consign little food for baby birds. Some plants and trees unfurl early and some caterpillars are unable to eat larger, tougher leaves. Ill-timed migrants may hatch their young after edible caterpillars have already metamorphosed into insects.

Birds scramble to adapt. New research documented 72 species that now lay their eggs a month early. Others are nesting further north. This spring, for the first time, all of Rutledge’s 25 bluebird nesting boxes on his land in Colorado remained vacant.

Many birds are on the move, wintering further north, shifting ranges toward the poles, or shifting to higher elevations. “But there’s only so far they can go,” says Haskell. She emphasized the need to protect land in places where birds are likely to be found in coming years.

Atlantic puffins, Northumberland, England, United Kingdom. Puffins nesting on Maine’s coastal islands aren’t finding enough fish to feed their young amid “marine heat waves” and intense storms. Scientists dubbed survivors “micro puffins”; they’re half the normal size. Image courtesy of Alexander Lees.

But as shifting species play musical chairs, they may face competition as they enter new areas. Wildlife photojournalist Steve Winter observed an early example while documenting the resplendent quetzal in a Guatemalan cloud forest in 1997. “Every time I found a nest, the chicks were killed by emerald toucanets,” Winter said. “They’d always lived at lower altitudes.”

It’s particularly challenging for specialists that need particular food. Atlantic puffins that nest on Maine’s coastal islands, for example, aren’t finding enough fish to feed their young amid “marine heat waves” and intense storms. Scientists dubbed survivors “micro puffins”; they’re half the normal size.

The complexity of climate change raises ethical issues, says BirdLife’s Allinson. Conservationists rarely move wildlife beyond their natural ranges, as newly introduced species can devastate ecosystems. But as climate-appropriate habitat shifts, he asks, “do we maintain [bird species] by moving them around the world?”

Meanwhile, existing and emergent diseases are adding risk, culling birds already weakened by climate change or other stressors. Some diseases have reached as far as Antarctica. Salmonella bacteria, for instance, got to Antarctica via cruise ships and are reportedly infecting Adélie penguins. The current avian flu outbreak is killing untold numbers of U.S. birds, including eagles and black vultures.

Invaders

Many island birds evolved in isolation without mammalian predators until humans arrived with the domestic animals and pests they brought along. The invaders took a huge toll on flightless birds: 68% of those known to science are gone. “Introduction of alien species has caused more extinctions to date than anything else,” Allinson says.

On South Pacific islands, rats and mice eat seabird chicks. “It’s impossible to find storm-petrels on Rapa,” says Tehani Withers, who heads island restoration for the Ornithological Society of Polynesia. Shearwater populations have also collapsed.

Locals compound the problem by dumping feral cats on remote islets to control rodents, but the rat-cat combination is doubly deadly. Cats are particularly efficient predators: Tibbles, a single cat owned by a lighthouse keeper, purportedly wiped out an entire species, the flightless Stephens Island wren, off the coast of New Zealand.

The brown tree snake is another notorious invasive. It arrived in Guam in the 1950s, possibly hitchhiking on a cargo ship from New Guinea, and wiped out the island’s birds. Introduced mosquitos that carry avian malaria and pox have made Hawai‘i the “bird extinction capital of the world.”

The greater sage grouse, an icon of the U.S. West, isn’t an island bird, but it’s a species that faces numerous threats, including invasive Asian cheatgrass. The weed thrives in disturbed soil, spreads like wildfire — and burns. “In the past five years, we’ve had over 10 million acres [4 million hectares] of cheatgrass fire in this ecosystem,” says Rutledge, adding that it destroys the sagebrush that grouse need to survive.

Population abundance indices for bird species dependent on major habitat types in (a) North America, (b) Europe, (c) India, and (d) Botswana and Uganda. Image courtesy of Lees et al. (2022).
Eradicating invasive species is key to saving island bird species. Image © Steve Cranwell.

Hunting

Hunting ranks as the fourth-largest threat to birds. They are eaten, killed for traditional medicine and sport, eradicated as pests, collected for the pet trade, and caught by fisherfolk as bycatch. Lees points out that, ultimately, “it’s irrelevant from the bird’s perspective whether it ends up in a cage, on someone’s mantle, or in someone’s stomach. It’s still removed from the breeding population.”

More than 50 shorebirds are among the victims, including endangered godwits and curlews, culled mostly for food during long migrations to and from Australia. The dickcissel, a sparrow-like migrant that overwinters in Venezuelan rice fields, has been hunted to near-extermination. Longline fishing rigs, stretching across 60 kilometers (40 miles) of sea and outfitted with 1,800 hooks, catch thousands of albatrosses and other seabirds.

Both the legal and illegal trades have mushroomed over the past three decades and decimated populations. Parrots and macaws are popular pets, prized by European and U.S. collectors. Some birds are still smuggled from the wild. Taped to smugglers’ bodies, stuffed into plastic bottles, drugged inside suitcases, and moved in every way imaginable, up to 80% die in transit. “They can fetch unbelievable sums,” Lees says. One online source quoted prices of up to $4,000 for an African gray parrot or scarlet macaw. The trade has decimated populations.

A red-backed shrike, a declining European grassland bird, seen here in Dobrich, Bulgaria. Image courtesy of Alexander Lees.

The so-called “Asian songbird crisis” centers in Java, where “There’s a strong culture of bird-keeping,” says Stuart Marsden, a conservation ecologist at Manchester Metropolitan University.

Trappers catch birds in Indonesia’s forests and sell them for both caged pets and songbird competitions. “There’s potentially more birds in captivity than there are in the wild,” Marsden says. Brazilians also have a long history of keeping pet birds, which they call xerimbabos: “something beloved.”

The once common yellow-breasted bunting is being eaten to extinction as a delicacy in China: numbers plummeted by 90% since 1980. The helmeted hornbill’s huge, solid beak is more valuable than ivory, carved and sold to wealthy Chinese buyers; it is now critically endangered.

Over the past 50,000 years, growing human populations, armed with ever-more sophisticated weapons, have wiped out at least 20% of all bird species — 469 so far.

The passenger pigeon was a high-profile hunting casualty. The species was once North America’s most abundant bird, with flocks so thick they blotted out the sun. That made them easy to shoot. Nobody thought so many could possibly disappear forever. The last one died in 1914.

These charts quantify the threats to the world’s birds. Data from BirdLife International. Image courtesy of Lees et al. (2022).

‘Elixirs of death’

Though Silent Spring brought global attention to DDT and helped get it banned, the world is still awash in manufactured chemicals. In January, researchers determined that the sheer volume of these pollutants — some 350,000 chemicals — has contributed to a global tipping point: Synthetic materials introduced into the environment have become too numerous to be safely controlled, say scientists, and therefore have transgressed the novel entities planetary boundary, threatening the stability of Earth’s operating system.

Pesticides, herbicides and rodenticides still pose major threats to birds’ survival, but there are occasional victories. After 20 years of controversy, the U.S. EPA finally banned the neurotoxic insecticide chlorpyrifos in 2021. The chemical was implicated in harm to 97% of all threatened and endangered wildlife, including more than 100 bird species. However, experts call such regulation a whack-a-mole approach. One biocide is banned; another hits the market.

A 2019 study found that in one year, the U.S. sprayed 322 million lbs (146 million kg) of pesticides that are banned in other countries. The U.S. uses 72 pesticides that are illegal or being phased out in the EU. Among them are widely used neonicotinoids. They poison birds in various ways — by contaminating insects they eat and leaving residues in plants, fruit and nectar. Eating just one “neonic”-coated seed can sicken or impair birds’ ability to navigate, or kill them.

Endangered hyacinth macaws, the largest of all parrots, can fetch up to $12,000 each on the black market. Image © Steve Winter.

Add in what Lees calls “a massive increase in herbicide use” and rodenticides, and the toll becomes exponential. Brazil, under President Jair Bolsonaro, has approved use of more than 290 pesticides and lowered scientific standards for toxicity. The country now ranks among the highest users of pesticides on Earth. Hyacinth macaws there have died due to “reckless use of pesticides,” but overall bird losses in Brazil are poorly documented.

Even well-meaning bird lovers are unknowingly causing harm. In the U.K., the 150,000 tons of feed people put out each year attracts rodents, which people kill with rat poison, then raptors feeding on the rodents and die. Pest control poisoning of voles, prairie dogs and moles in the U.S. West also eradicates hawks, owls, and even songbirds that eat maggots on carcasses.

Farmland has become inhospitable for many migratory and grassland species as farmers leave less wild habitat and use more pesticides. These bird groups have taken substantial hits in both the U.S. and Europe. Lees uses shrikes — predatory songbirds — as an example. “Being a shrike in the Anthropocene appears to be very difficult,” Lees says. Without large insects to eat, Japan’s red-backed shrike, Europe’s great shrike and the U.S. loggerhead shrike are all disappearing.

IUCN Red List Index for all bird species, showing trends in aggregate survival probability over time. Examples of species downlisted on the IUCN Red List Index to lower categories of extinction risk (green) or uplisted to higher categories (red) — and the threats driving these changes. Abbreviations: CR, Critically Endangered; EN, Endangered; EW, Extinct in the Wild; LC, Least Concern; NT, Near Threatened; VU, Vulnerable. Image courtesy of Lees et al. (2022).
The secretary bird, a highly threatened African raptor, is typical of many bird species in that its decline has been linked to multiple causes including habitat degradation, disturbance, hunting and capture for trade. Ngorongoro Conservation Area, Ngorongoro Crater, Tanzania. Image courtesy of Alexander Lees.

The way forward

Amid so much death and loss, it’s important to highlight successes. “Many bird species that are alive today wouldn’t be without conservation action,” Allinson points out; about 32 species have been brought back from near-extinction since 1993.

Despite a voracious market for songbirds in Indonesia, Stuart Marsden has seen comebacks for seemingly hopeless cases like the Bali myna — accompanied by an explosion in environmental activism, with people going from loving caged birds to loving them in the wild. In French Polynesia, Tehani Withers is training locals to trap rats, pull non-native weeds, and cull feral goats — with seabirds again nesting on these islands. Scientists are working with fishing fleets to keep albatross off longline hooks.

Restoring, connecting and protecting the ecosystems birds need to survive — along with targeted strategies to bring species back — could save many more. This dovetails neatly with other environmental goals, says Lees, such as cutting carbon emissions from deforestation and addressing the larger “sixth mass extinction” crisis.

It’s not an insurmountable challenge. There are precedents where global, national and corporate collaboration averted crisis, including the 1987 Montreal Protocol that protected the planet’s ozone layer.

Examples of successful bird conservation efforts; The top 10 actions implemented for species that have been downlisted on the IUCN Red List. Data from: BirdLife International. Images via Lees et al. (2022).

“We can reverse the situation,” says Withers, but it will require political will, public support, and investment. It would cost about $70 billion a year to reverse what the World Economic Forum calls “a catastrophic decline in biodiversity.” While that’s a huge sum, it’s a small amount when compared with environmentally damaging expenditures: In 2020, the world’s governments subsidized coal, oil and gas to the tune of $5.9 trillion. And in 2021, the world’s 10 largest companies brought in $31.7 trillion in profits.

Choosing not to act will have domino-effect consequences, says Allinson. Losing birds “undermines the ability of ecosystems to function, with potentially devastating consequences for all life, including our own.”

While sweeping changes are needed, experts note the many ways individuals can make a difference. Turn out lights in big buildings during migration season. Make climate-friendly energy choices. Stop dousing lawns and gardens with chemicals. Vote for political candidates who prioritize planetary health.

“At this point, every bird makes a difference,” says Rutledge.

Kirtland’s warbler, a conservation success story, seen in Crawford, Michigan, U.S. Image courtesy of Alexander Lees.

Banner image: The spotted tody-flycatcher, native to South America and the Caribbean. Image courtesy of Alexander Lees. 

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