Perhaps one of the world’s best known fossils is Archaeopteryx. With its beautifully preserved feathers, it has long been regarded as the first bird in the fossil record, and is often called “the icon of evolution”. Only a handful of specimens have ever been found, its elusivity adding to its fascination.

You know that feeling when you miss a flight because you overslept after a night of getting plastered? Maybe not.

A large-scale analysis of bird migrations in the contiguous United States confirms what ornithologists and amateur birders already suspected: Overall, birds’ seasonal long-distance flights are happening earlier than they did a quarter of a century ago.

Researchers have revealed that North American birds are declining at an accelerating rate in three regional hotspots associated with intense agriculture.

Wild bird numbers declined at an accelerating rate in California, the Midwest and the Mid-Atlantic between 1987 and 2021. Across these hotspots, losses were associated with high-intensity agriculture, according to the study.

Although the study, published Feb. 26 in the journal Science, shows a correlation between declining bird populations and intense agriculture, it doesn't definitively prove that agriculture is driving the increased decline or identify which agricultural activities might be responsible.

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However, signs of intense agricultural activity consistently proved to be the best predictor of increased bird decline, which mirrors similar research conducted in Europe. The researchers also found that declines were stronger in warming areas, suggesting that rising temperatures due to climate change were driving some bird disappearances.

 
Birds perform important roles in the ecosystem, including spreading plant seeds and keeping insect populations under control. For decades, scientists have been concerned that bird populations are falling due to human activities, both in North America and globally — a plight shared by many other animals. What's special about the new research is that it reveals how the decline in North America has accelerated since the late 1980s.

"We are not talking about the decline but the acceleration of the decline," study lead author François Leroy, a postdoctoral researcher in macroecology at The Ohio State University, told Live Science. "We see that this decline is getting faster and faster with the intensification of human activities."

Leroy and his colleagues mapped bird decline by studying data from the North American Breeding Bird Survey, which is an annual surveying effort by professional biologists and skilled amateurs to monitor bird populations across North America. As a part of the survey, participants walk along specific routes and record the birds they find.

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The researchers focused on specific routes with enough data to measure the rate of decline over 35 years. These routes were primarily in the U.S. and included 261 bird species. Across all of the species surveyed, the overall abundance of birds fell by at least 15%, with significant drops documented in about half (122) of the species and accelerating declines reported in about a quarter (63) of the species. Common birds ‪—‬ like red-winged blackbirds (Agelaius phoeniceus), house finches (Haemorhous mexicanus) and American crows (Corvus brachyrhynchos) ‪—‬ were among the native species found to have suffered an accelerated decline.

The study focused on the rate of decline in specific routes, so it's unclear 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 estimated that the North American bird population decreased by 2.9 billion individual birds between 1970 and 2017. That estimate equated to a drop of 29%, which is almost double the 15% decline documented in the new study. However, the 2019 study also covered an earlier and longer time period when there may have been more severe losses.

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People only started surveying 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 forced passenger pigeons (Ectopistes migratorius), a species estimated to have once had a population of 3 billion to 5 billion, to extinction in 1914.

What caused the "birdemic"?
The new study demonstrated that birds were incurring losses not just at the species level but across whole families of species and across different habitats. To better understand the worrying trend, the researchers compared the bird data to potential contributing factors, such as temperature change, rainfall and land-cover changes.

The acceleration of bird decline coincided with large areas of croplands and high usage of fertilizers and pesticides, which are signs of intense agriculture. This tracks with research in Europe that has found that agricultural intensification has negatively impacted bird diversity.

Intense agriculture can destroy, change and break up traditional bird habitat. The amount of land used for farming in the U.S. hasn't changed that much since the 1980s. Agriculture has become more consolidated in that time, with a decline in midsize farms and a shift to larger farming operations, but there's slightly less land being used for farming overall. Thus, the bird losses can't be blamed solely on the amount of farmland. However, they could be the result of changes in farming practices.

Leroy said that from the new study, it's not really possible to say which specific practice in agriculture is the worst for bird losses. However, he noted that from previously published studies, it seems like 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 drops, particularly in birds that feed on invertebrates. Most disappearing bird species depend on insects for food, and insects are in steep decline as they are killed through the use of pesticides. Birds also consume pesticides directly.

Leroy said he would like to see what farmers think about the correlation between agricultural intensification and bird losses. He and his co-authors also noted in the study that agriculture warms landscapes by reducing the amount of vegetation and altering its properties, which may then amplify warming impacts on birds.

While the findings were mostly bad news for birds, there were some bright spots. For example, the researchers found some local increases in forest bird populations, which likely benefited from the reforesting of old farmland. There was also a small pocket of land just north of the U.S.-Canada border where the overall abundance of birds increased — the only region in which this occurred. However, Leroy said he had "no clue" why this was the case.

"It doesn't mean that Canada is doing better because if you look at other regions in Canada, there were also some significant declines," he added.

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Birds have, for centuries, been captured from the wild to be kept in cages – valued for their looks, songs and ability to imitate sounds.

The avian influenza outbreak in South Africa this year has led to the culling of millions of birds in the country, resulting in a 30% reduction in the production of hatching eggs. Poultry farmers, already battling with loadshedding and high costs, and local consumers are paying the price.

In South Africa, the wattled crane population has declined by 35% over 20 years, leading to the population falling to numbers as low as 131 in 1995. In a water-scarce country like South Africa, wetlands play a crucial role through the storage, purification, stream-flow regulation and recharging of groundwater.

A one-ounce, stocky blur of blue that warbles a melodious song, rarely strays far from its breeding area, enjoys foraging from a perch, and loves to sleep in a nest of twigs in pre-existing cavities may not seem like an excellent candidate for the annihilation of one’s foes.

Which helps explain why western bluebirds, and many of their twee counterparts, have “flown” under the radar for so long.

“People are still surprisingly ignorant about the bluebird phenomenon,” says Tom Clark, who is based in Napa, owns and manages vineyards and works as a consultant for growers hoping to lure bluebirds and swallows into the vines. “There’s a growing awareness in Napa and Sonoma through word of mouth, and the number of wineries and growers I’ve built and installed boxes for in the past three years has gone up exponentially.”

As winegrowers slowly but surely see the positive impact of these birds on the health of their vineyards and the quality of their wines, Clark says the price of entry (about US$65 per custom-built box, $110 for a site visit) is getting worked into annual farming budgets.

How many insects can these birds consume?
It’s hard to track just how many pests bluebirds and other songbirds manage to eat because they are constantly on the move, and their prey is minuscule. But Dr. Julie Jedlicka, associate professor of biology at Missouri Western State University, managed to analyse DNA fragments of the birds’ faeces in a survey in California’s vineyards.

The analysis, published in The Auk: Ornithological Advances, found that bluebirds ate primarily herbivorous insects, including chronic vineyard pests.

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Breanna Martinico, PhD, a human-wildlife interactions advisor at the University of California, Davis, is in the midst of a DNA-based survey in Napa with other scholars considering which birds target pests in vineyards and what type of habitats they prefer.

“From our initial findings, conducted over two years, we’re finding that bluebirds and tree swallows are attracted to viticultural habitats with nest boxes,” Martinico says. “They like to forage for insects about 200 meters from the box, or closer. Our data shows that bluebirds and tree swallows are consuming alfalfa hoppers, vine mealybugs and blue-green sharpshooters. Bluebirds are also eating variegated and Virginia creeper leafhoppers. These are all vineyard pests!”

The implications, Martinico maintains, are vast.

“If we can reduce the use of chemicals by creating habitats for birds, it’s good for everyone,” Martinico says. “A lot of songbird populations are down because of overdevelopment and invasive species. This helps them, and it helps vineyard owners. It’s also much better for the environment. Imagine if we implemented these practices everywhere?”

A natural solution to chemical dependency
The implications have also arrested the attention of Ivo Jeramaz, winemaker and vice president of vineyards and production at Grgich Hills Estate in Napa. The winery became certified organic in 2006, then Regenerative Organic Certified in 2023. While reducing inputs and boosting biodiversity in the vineyard is part of Jeramaz’s vision for the estate vineyards, he admits that the transition has required adjustment.

“Biodiversity can be a double-edged sword,” Jeramaz says. “Because we steward our land without chemical pesticides and encourage a diverse host of plants and animals to call our vineyards home, creatures of the pestilent variety can take up residence where we prefer them not to.”

To prevent vine mealybugs, leaf hoppers and sharpshooters from “devouring” the vines, he says they’ve installed hundreds of bird boxes designed to lure bluebirds and tree swallows into their vines.

“Our vineyards are an ecosystem, where every creature has a niche to fill,” he says. “While this means that we will never fully eradicate pest species the way a heavy dose of pesticides might, it does mean that we build resilience, ensuring our vineyards can adapt to new environmental stressors more effectively.”

Designing vineyards as ecosystems
At Two Mountain Winery in Washington’s Yakima Valley, vineyard operations manager Patrick Rawn says that he approaches their 430-acre estate as an entire ecosystem, instead of a vineyard.

While they don’t have nest-boxes, and bluebirds aren’t regularly spotted in the region, Rawn says the vineyard team is “developing and reclaiming unfarmable spaces on our farm to promote a natural habitat for the songbirds as part of the ecosystem.”
Since replanting these areas with native plants and shrubs, which are attracting goldfinches, warblers, wrens and magpies.

“We are still in the early stages of directly measuring the impact on bugs,” Rawn says. “But we are starting to see macro-level reduced pest pressure since undertaking the project two years ago.”