Logan Parker anticipates the arrival of the male black-throated blue warbler each spring near his home in Maine. He is always struck by two things: the bird’s remarkable beauty and the extensive journey it has taken from its winter habitat in Central America or the Caribbean.

With their captivating black masks and vivid blue and white plumage, Parker comments, “They appear so fragile. It is surprising to think they travel such long distances to breed here.”

Historically, these birds and others have synchronized their long migrations with nature’s cycles, like trees unfurling their leaves. However, that connection is changing.

Spring, which used to arrive with a consistent rhythm of nature’s awakening, is now arriving earlier, influenced by rising temperatures. Ellen Robertson, a co-author of a recent study on bird migrations during her postdoctoral research at Oklahoma State University, explains that many birds, including the black-throated blue warbler, are now arriving “out of sync” with the peak food availability due to this shift. For instance, they may reach their nesting sites after the peak emergence time for insects.

Robertson is among many researchers dedicated to uncovering the complexities of migrating birds and the long-term impacts of climate change on their survival.

They are leveraging an expanding collection of data that provides an unprecedented understanding of bird migration patterns. Recent studies have utilized over three decades worth of radar data, satellite information, remote sensing, and citizen science initiatives. Vast quantities of long-term data are being gathered from bird watchers, banding stations, and breeding surveys.

Andrew Farnsworth, a visiting scientist at Cornell University, remarks on the remarkable advancements in technology related to radar, acoustic remote sensing, and machine learning.

He stresses that the ability to collect, analyze, and visualize large datasets is crucial for understanding how climate change affects migratory patterns.

The Impact of Warmer Springs on Bird Migration

Spring has always been unpredictable regarding when it arrives—sometimes early, sometimes late. However, researchers have indicated that data collected over many years reveals that warmer temperatures are causing springs to arrive progressively earlier, particularly in northern areas.

This year, several regions in the U.S., especially the Eastern part, experienced spring weather 10 to 15 days earlier than the long-term average, noted Scott Loss, a professor of natural resource ecology and management at Oklahoma State University and one of Robertson’s co-authors. For instance, cherry blossoms in Washington, D.C., bloomed earlier than ever recorded.

Loss also observes alterations taking place in other seasons: “Our winters are becoming shorter, and our summers are stretching longer.”

By examining over 20 years of nighttime radar data tracking bird movements across the United States, recent research highlighted the changes in migration patterns.

“We aren’t just observing a single location or species adapting; the entire group of migratory birds is arriving sooner than before,” explained co-author Kyle Horton, an assistant professor at Colorado State University. “It’s not merely the beginning or ending of migration that’s affected.”

“This strongly indicates that birds are reacting to these environmental changes,” he continued. Similar trends of earlier migration have been observed in both the Caribbean and Mediterranean regions.

A global report from the United Nations Convention on the Conservation of Migratory Species of Wild Animals released this year identified climate change as one of the leading threats to migratory birds, along with posing additional risks for other migratory species, such as wildebeests.

Some birds are ‘out of sync’

Increasing temperatures are causing certain bird species to revise their migration patterns, arriving at their spring breeding sites several days or weeks earlier than in the past.

Conversely, some species struggle to adapt. They synchronize their migration with daylight hours rather than temperature shifts, meaning they follow the calendar despite the warming climate.

As flowers bloom, trees begin to leaf, and insects emerge sooner than they used to, these birds often miss the opportunity to feed.

“By the time you reach your breeding grounds, you’ve arrived too late to benefit from the significant insect hatch you depended on while raising your young,” noted Melanie Smith, digital science and data products director at the National Audubon Society.

Robertson and Loss, among four co-authors, researched the migrations of 150 bird species along flyways stretching from South America to the Arctic, utilizing remote sensing and satellite data to analyze how bird migration matched the timing of spring growth.

In a study published in March in the Proceedings of the National Academy of Sciences, they found that migration timing for some species correlated more closely with the historical average date for peak spring growth rather than the current timing, suggesting that they are adhering to outdated calendar dates, as stated by Loss.

Robertson expressed concern about long-distance migrants, like the black-throated blue warbler, asserting that migratory journeys are “extremely energetically costly” for small birds like this species, weighing around a third of an ounce, comparable to the weight of two nickels.

Migration has already been significantly disrupted due to urban development and the reduction of green spaces along critical migratory routes, stated Smith. When climate change is added to the mix, with its variability in weather, precipitation, heat, and wind, it creates an even tougher environment for these birds.

The team associated with Robertson found that long-distance migrants, those traveling from southern Central America or South America to northern boreal forests in the U.S. and Canada, are less adaptive to change than shorter-distance migrants like American robins or red-winged blackbirds, which may only fly a few hundred miles.

Due to their extensive travels, the birds that migrate the farthest lack access to real-time local weather conditions, preventing them from adapting swiftly, according to Robertson.

Cold snaps occur despite warmer springs

Research indicates that rising temperatures are altering the patterns of both birds and the insects they depend on. A 30-year study at Cornell University in New York on tree swallows and aquatic insect emergence revealed various threats induced by climate change.

As temperatures in May increased, bird nesting shifted to earlier dates, reported David Winkler, a senior research biologist and retired professor from Cornell University. A study he co-authored with Ryan Shipley found that tree swallows advanced their egg-laying by approximately three days each decade.

This means that the chicks now face exposure to unfavorable weather events.

Birds are experiencing harsh cold snaps twice as frequently now as they did in the 1970s. This study indicates that even with the general trend of rising temperatures, late-season cold air blasts still occur at roughly the same times as they used to. Just one bad weather event can decrease the survival rate of young birds by over 50%.

For at least 25 years, Winkler and his team have been counting flying insects at their research site daily, using essentially an aerial vacuum cleaner. Their observations show that the timing and diversity of insect populations are shifting due to warmer weather.

Species adapted to cold, like large aquatic flies, are being supplanted by smaller insects, such as midges and gnats, which do not provide as much nutrition for birds, as Shipley explained in a previous interview. The supply of insects, particularly those rich in nutrients, significantly affects the survival of chick birds.

An adult tree swallow incubating her eggs can manage for a day or two without many insects, but this is not the case for growing chicks that need warmth to survive, Winkler noted. Sometimes, when adult swallows struggle to find enough food, they may leave their nests temporarily for a couple of days or even abandon them entirely in search of better food sources.

As time goes on, more changes are expected to occur as birds and their ecosystems endure the severe conditions anticipated, according to Farnsworth.

While Parker enjoys birdwatching in Maine, he is also responsible for tracking two migratory bird species: the Eastern whippoorwill and the common nighthawk, known to be among the longest migratory birds in North America.

To protect these migratory species, Parker emphasizes the importance of showcasing the remarkable journeys these birds take each year and rallying public support to conserve their habitats, breeding areas, and migration routes. “Our goal is to promote responsible stewardship,” he remarked.

Dinah Voyles Pulver reports on climate change, wildlife, and the environment for YSL News. You can reach her  on Twitter @dinahvp.