Birds are declining faster and faster in 3 US hotspots, new study finds
Bird populations are plummeting across North America. And in some hot spots, their decline is accelerating, a new study reveals.
The number of wild birds declined at an accelerating rate in California, the Midwest and the mid-Atlantic between 1987 and 2021. In these hot spots, losses were associated with high-intensity agriculture, the study found.
Birds play an important role in the ecosystem, including spreading plant seeds and keeping insect populations in check. For decades, scientists have worried about declining bird populations due to human activities, both in North America and around the world – a fate shared by many other animals. What’s unique about this new research is that it reveals just how much the decline in North America has accelerated since the late 1980s.
“We are not talking about decline but about the acceleration of decline,” lead author of the study François Leroypostdoctoral researcher in macroecology at Ohio State University, told Live Science. “We see that this decline is accelerating more and more with the intensification of human activities.”
Leroy and his colleagues mapped bird declines by studying data from North American Breeding Bird Surveywhich is an annual survey effort conducted by professional biologists and trained amateurs to monitor bird populations across North America. As part of the survey, participants walk specific routes and record the birds they find.
The researchers focused on specific routes with enough data to measure the rate of decline over 35 years. These routes took place primarily in the United States and included 261 bird species. For all species studied, overall bird abundance declined by at least 15%, with significant declines documented in about half (122) of species and accelerated declines reported in about a quarter (63) of species. Common birds — such as red-winged blackbirds (Agelaius phoeniceus), house finches (Haemorhous mexicanus) and American crows (Corvus brachyrhynchos) — were among the native species whose decline has accelerated.
The study focused on the rate of decline of specific routes. It is therefore difficult to know how many individual birds were lost across the entire continent during the study period. However, previous research has found that billions of birds have disappeared in recent decades.
A 2019 study published in the journal Science The North American bird population is estimated to have declined by 2.9 billion birds between 1970 and 2017. This estimate equates to a 29% decline, almost double the 15% decline documented in the new study. However, the 2019 study also covered an earlier and longer period during which losses could have been more severe.
People only started studying North American birds in the second half of the 20th century, but we’ve been killing them directly and indirectly for much longer than that. For example, commercial hunting by humans has forced homing pigeons (Migratory ectopists), a species believed to once have had a population of 3 to 5 billion peopleuntil extinction in 1914.
What caused “birdemia”?
The new study demonstrated that birds were experiencing losses not only at the species level, but also across entire families of species and across different habitats. To better understand this worrying trend, the researchers compared the bird data to potential contributing factors, such as changes in temperature, precipitation and land cover changes.
The accelerating decline of birds has coincided with large areas of cultivated land and intensive use of fertilizers and pesticides, signs of intense agriculture. This follows research in Europe which showed that agricultural intensification had a negative impact on bird diversity.
Intensive agriculture can destroy, modify and destroy traditional bird habitat. The amount of land used for agriculture in the United States has not changed as much since the 1980s. Agriculture has become more consolidated over this period, with a decline in mid-sized farms and a transition to larger farms, but there is slightly less land used for agriculture overall. Thus, bird losses cannot be attributed solely to the area of agricultural land. However, they could be the result of changes in agricultural practices.
Leroy said that from the new study, it’s not really possible to say which specific practice in agriculture is worst in terms of bird losses. However, he noted that based on previously published studies, it appears that pesticide use is one of the main suspects.
A 2023 study published in the journal PNAS found that the use of pesticides and fertilizers was the key to agricultural intensification being the main pressure behind most bird population declines, particularly in birds that feed on invertebrates. Most extinct bird species depend on insects for foodAnd insects are in sharp decline because they are killed by the use of pesticides. Birds too consume pesticides directly.
Leroy said he would like to know what farmers think about the correlation between agricultural intensification and bird loss. He and his co-authors also noted in the study that agriculture warms landscapes by reducing the amount of vegetation and changing its properties, which can then amplify the impacts of warming on birds.
Although the results were mostly bad news for the birds, there were some bright spots. For example, researchers noted a local increase in populations of forest birds, which likely benefited from the reforestation of former agricultural lands. There was also a small pocket of land just north of the Canada-US border where the overall abundance of birds increased – the only region in which this happened. However, Leroy said he had “no idea” why that was the case.
“That’s not to say that Canada is doing better, because if you look at other parts of Canada, there have been significant declines as well,” he added.
