Climate collapse is happening too fast for migratory birds

This story was originally published by High Country News and appears here as part of the Climatic desk collaboration.

At first glance, the male western tanager looks like a small llama, with its ruby ​​head blending perfectly with its bright lemon-colored body. Females are less showy, a dusty yellow color. The birds winter in southern Central America and can be found in a variety of habitats, from the cool cloud forests of central Costa Rica to the southeastern Sonoran deserts of western Mexico. In early March, they prepare to migrate thousands of miles to the coniferous forests of the Mountain West, flying through grasslands, deserts, and occasionally suburban backyards.

To feed themselves on their long journey, western tanagers feed on insects and berries. Like most migratory birds, they eat constantly when not in the air. But as global climate change causes spring to start earlier, birds like western tanagers arrive at their destinations after greening, when flowers begin to bloom and insects emerge. According to a study published in early March in the journal PNAS, this type of temporary mismatch between migrants and their food sources, which is occurring across North America, could have dire consequences for the survival of migratory birds. “When discussing climate change, we often focus on warming,” said Scott Loss, an associate professor at Oklahoma State University and lead author of the study. “But the length and timing of seasons, such as when winter ends and spring begins, are some of the most dramatic effects of climate change.”

Loss and his colleagues used satellite images from 2002 to 2021 to calculate the average onset of spring greening along the typical migratory routes of 150 North American bird species, and then compared that time to the current greening, or year. most recent for which they had data. They discovered that spring does indeed begin earlier on birds’ migratory routes. The trend continued this year, when, after an unusually mild February, leaves and flowers emerged up to 14 days earlier than expected along the West Coast, making this year’s greening the earliest on record. .

The authors then turned to a trove of observations from citizen birders of eBird to track bird migration. The analysis showed that, as spring advanced, approximately 110 of 150 bird species failed to keep up with their migration over time. “Many of these birds tracked long-term greening averages more closely than current greening,” said study co-author Ellen Robertson, who was a postdoctoral researcher at Oklahoma State University when she conducted this research. Other studies have found that many bird species are adapting to climate change by migrating earlier, but this study shows that it may not be early enough to keep pace with climate change.

A Green-winged Teal in the Fernhill Wetlands near Carnation, Oregon. The species was one of 110 identified in a study as failing to reach its ideal migration timing associated with spring greening. Photo by Richard Griffin/CC via Flickr

“The paper continues to build this picture of the extent and pervasiveness of birds’ inability to follow seasonal changes caused by climate change,” said Morgan Tingley, an ornithologist and associate professor at the University of California, Berkeley. Temporal mismatches between birds and their food could affect whether birds survive the migration and how many chicks they have. TO recent study from Tingley’s lab showed that songbirds that arrive at their spring breeding grounds before or after plants emerge have fewer offspring than those that arrive in time with the onset of spring, for example.

Previous studies have focused primarily on songbirds in eastern North America, Tingley said, but this new research shows that bird species in the west and at different levels of the food web could be equally vulnerable. However, Tingley noted that some questions remain unanswered. While previous studies show that a temporal mismatch could have serious consequences for herbivorous songbirds, for example, it is unclear whether the same is true for birds that feed on other animals, such as insects.

The impressive feat of migration has captivated humans for millennia, yet scientists know very little about how birds manage to fly so far, up to tens of thousands of miles per trip, or why exactly they leave when they do. The migratory signals that birds depend on are countless: temperature, day length, geographical features, the stars and even the Earth’s magnetic field, as well as the instructions encoded in their genetics. Some environmental signals, such as temperature, are likely to be affected by climate change. But others, such as the length of the day, are not. “That could be one reason why some (migratory) birds are more affected by climate change (than others),” Robertson said.

Climate change is happening too fast for migratory birds. #ClimateChange #MigratoryBirds

A male Townsend’s Warbler at the Sobrante Ridge Regional Reserve in California. One study found that birds migrating longer distances had a greater mismatch between greening and migration. Photo by Becky Matsubara/CC via Flickr

The study found that birds migrating longer distances had a greater mismatch between greening and migration. Researchers suspect this is because even if the birds track temperature or other migratory cues in their winter home, they can’t know what conditions are like further away: whether spring comes earlier along their migratory route or to their destination than in its place of origin. winter headquarters. Long-distance migrants also tend to rely more on their genetic coding to know when to start their journey.

Around the world, bird populations are declining. Bird numbers in North America have declined more than 30 percent since 1970. Even abundant species, such as crows, have suffered a population decline. Loss said research on migration could inform conservation efforts in the future.

“Part of this is knowing which species are vulnerable to various threats,” Loss said. “This increases knowledge about the vulnerability of a wide range of bird species.”

And he hopes the information will serve to highlight the urgent need to reduce greenhouse gas emissions as quickly as possible: “It’s really important, if we can’t tackle climate change immediately, to try to stop habitat loss as much as we can. “

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