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Bye-Bye Birdies: Almost 3 Billion Birds Disappeared From North America's Skies In Less Than 50 Years

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A new study reports that birds living or breeding in Canada and the United States have declined by an average of 29% since 1970

Minette Layne via a Creative Commons license

Thanks to human actions, most of North America’s bird populations are declining. A recently published study reports that North American bird populations have declined by an estimated 2.9 billion individuals (29%) since 1970. Most of the lost birds are common species, including familiar backyard birds, such as sparrows, finches and warblers, that live or breed throughout the United States and Canada.

“Multiple, independent lines of evidence show a massive reduction in the abundance of birds,” ornithologist and lead author, Ken Rosenberg, a senior scientist at the Cornell Lab of Ornithology and the American Bird Conservancy, said in a press release.

“We expected to see continuing declines of threatened species. But for the first time, the results also showed pervasive losses among common birds across all habitats, including backyard birds.”

Dr. Rosenberg collaborated with scientists from Canada’s environment agency and the U.S. Geological Survey to investigate how many birds have been lost from North America. This study was possible because birds are probably the best-monitored animals on Earth, and have been for many decades, especially due to long-running citizen science projects like the Breeding Bird Survey and the Christmas Bird Count.

“These data are consistent with what we’re seeing elsewhere with other taxa showing massive declines, including insects and amphibians”, said co-author Peter Marra, senior scientist emeritus and former head of the Smithsonian Migratory Bird Center when this study was initiated, who now is director of Georgetown University’s Environment Initiative.

The study notes that birds are indicators of environmental health, and their decline signals that natural systems across the U.S. and Canada are now being so severely impacted by human activities that they can no longer support the same rich wildlife populations.

“It’s imperative to address immediate and ongoing threats, both because the domino effects can lead to the decay of ecosystems that humans depend on for our own health and livelihoods -- and because people all over the world cherish birds in their own right”, said Professor Marra. “Can you imagine a world without birdsong?”

Birds are important indicators of ecological health, thus, this sweeping loss of birds -- especially common species -- indicate that a comprehensive ecological and environmental unraveling is underway. These losses indicate that severe, widespread biotic changes and ecosystem impacts are echoing throughout the entire food web, including pollinators, predators and prey. Basically, wild birds are unwitting (and unwilling) canaries in North America’s ecological coal mine.

“Declines in abundance can degrade ecosystem integrity, reducing vital ecological, evolutionary, economic, and social services that organisms provide to their environment”, the authors write in their paper.

Three billion goodbyes?

Dr. Rosenberg and his collaborators collected their numbers from 12 databases incorporating nearly 50 years of data amassed by multiple monitoring projects and citizen scientist surveys, including the annual North American Breeding Bird Survey and the Christmas Bird Count, throughout the Unites States and Canada.

“Citizen-science participants contributed critical scientific data to show the international scale of losses of birds”, co-author John Sauer of the U.S. Geological Survey pointed out. “Our results also provide insights into actions we can take to reverse the declines.”

Dr. Rosenberg and his collaborators quantified the net change in abundances of 529 species by integrating estimates of the population size across each species’ range along with 48-year population trajectories. These 529 species represent 76% of the birds that breed in North America.

Dr. Rosenberg and his collaborators then increased the area covered by their analysis by including data collected by a network of 143 NEXRAD weather radars across the contiguous United States, which can monitor areas that are not surveyed very often by on-the-ground efforts. Using these independently derived -- and nonhuman -- data, Dr. Rosenberg and his collaborators could estimate long-term changes in the movement of birds through the nighttime skies during spring migration between 2007 and 2017. NEXRAD radar data showed a 14% decline in spring migration during the past decade.

doi:10.1126/science.aaw1313

Combining and analyzing these data allowed Dr. Rosenberg and his collaborators to uncover extensive continent-wide population-level changes; they estimated that nearly 3 billion individual birds disappeared since 1970. Just 12 bird families represented 90% of the disappeared bird species examined (Figure 3A), including many of North America’s most familiar birds such as sparrows, warblers, finches and swallows.

The hardest-hit birds live on grasslands and prairies and other wide-open spaces. A 53% plunge in grassland birds -- more than 700 million birds of 31 species, included the loss of 139 million individual western and eastern meadowlarks, two species of large yellow-breasted songbirds with distinctive and clear flute-like songs -- vanished since 1970.

Alan Vernon via a Creative Commons license

The analysis found that meadowlarks weren’t unusual: 74% of all grassland bird species examined are declining, probably due to intensified agricultural practices that swallow up and destroy grassland habitats, smothering these fields under huge clouds of pesticides that kill the insects that many of these birds eat.

Birds living in virtually all forested habitats also showed sharp declines, with a cumulative reduction of more than 1 billion individual birds since 1970.

North American sparrows, a group of “little brown birds” with evocative songs that often live in our backyards and eat from our bird feeders, lost nearly one quarter -- 750 million -- of their numbers in the last 48 years (Figure 3A and C).

Cephas via a Creative Commons license

Even red-winged blackbirds, common denizens of wetlands and marshes throughout most of North America, declined by an estimated 92 million individuals (Figure 3A and C).

Shorebirds, a group that is already threatened by extensive damage to their coastal habitat by development, disturbances by people, their vehicles and their pets, and by rising sea levels, were also hard hit with more than a 30% decline (Figure 3D).

Brocken Inaglory via a Creative Commons license

Perhaps most concerning were the steep declines seen for ten introduced invasive species. These are highly adaptable species that thrive under what appears to be the most adverse of conditions. For example, European starlings, which are highly adaptive generalists that often live in close proximity to urban and suburban areas, declined by an astonishing 63% (Figure 3D and E). This reflects similar population trends in starling populations in Europe (more here). Indeed, if starlings are experiencing problems, this suggests something serious is afoot.

Tim Sackton via a Creative Commons license

Most of the lost birds (more than 2.5 billion birds) are widespread and common species that play outsized roles in local food webs and ecosystem functioning, ranging from seed dispersal to pest control (Figure 3).

doi:10.1126/science.aaw1313

Of the 67 avian families surveyed, 38 showed a net loss in total abundance, whereas 29 showed gains (Figure 3B), indicating that the overall species composition of bird communities is changing.

“While not optimized for species-level analysis, our model indicates 19 widespread and abundant landbirds (including 2 introduced species) each experienced population reductions of >50 million birds”, the authors wrote (ref).

Their analyses estimate that 2.9 billion birds have disappeared since 1970.

“Three billion is a lot of birds, but there are a lot of birds anyway, so what does it mean?” asked biostatistician Robert O’Hara, a professor of statistics at the Norwegian University of Science and Technology (Norges teknisk-naturvitenskapelige universitet, or NTNU), who was not part of the study. “I’d trust the 29% number much more than 3 billion.”

“I think the trends in relative abundance are probably reasonably good”, Professor O’Hara added before noting that “the absolute number [3 billion] does not have any validation in the study so we don’t know how ‘true’ this number is.”

Nevertheless, all the data agree that many bird populations are declining -- although some species are experiencing a more serious decline than others.

Waterfowl may show us the road back to recovery

But not all bird families have declined. For example, many raptors, some of which which nearly went extinct, are doing extremely well since the 1970s after the pesticide DDT was banned and the birds were protected by endangered species laws enacted in both the United States and Canada.

Joe Ravi via a Creative Commons license

Waterfowl (ducks, geese and swans) populations have also made enormous gains over the past 48 years, which likely result from concerted conservation efforts by hunters and billions of dollars of government funding designed to restore and protect wetlands where these birds are found.

Unfortunately, meadowlarks and sparrows do not have an organized, active group of people to advocate for their continued existence, and these birds’ populations have not declined enough to fall under federal protection.

However, a good place to start conservation efforts could be working towards expanding government programs that reward sustainable agriculture practices that use fewer pesticides and offer incentives to farmers to set aside hedgerows, trees and grassy margins where birds thrive.

Ordinary people can also help wild birds by keeping their cats indoors at all times, turning off outdoor lights during spring and autumn migration, and reducing or ending the use of pesticides on their property.

“It’s a wake-up call that we’ve lost more than a quarter of our birds in the U.S. and Canada”, said co-author Adam Smith, a senior biostatistician for Environment and Climate Change Canada.

“But the crisis reaches far beyond our individual borders. Many of the birds that breed in Canadian backyards migrate through or spend the winter in the U.S. and places farther south—from Mexico and the Caribbean to Central and South America. What our birds need now is an historic, hemispheric effort that unites people and organizations with one common goal: bringing our birds back.”

Source:

Kenneth V. Rosenberg, Adriaan M. Dokter, Peter J. Blancher, John R. Sauer, Adam C. Smith, Paul A. Smith, Jessica C. Stanton, Arvind Panjabi, Laura Helft, Michael Parr, and Peter P. Marra (2019). Decline of the North American avifauna, Science, published online on 19 September 2019 ahead of print | doi:10.1126/science.aaw1313

Bye-Bye Birdies: Almost 3 Billion Birds Disappeared From North America’s Skies In Less Than 50 Years | @GrrlScientist

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