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Deteriorating habitat conditions caused by climate change are taking their toll with the timing of bird migration. A new study shows that birds can partially compensate for these changes by delaying the start of spring migration and making the trip faster. But the strategy has a cost: a drop in overall survival. Findings by researchers from Cornell University, University of Maryland and Georgetown University are published in the journal Ecology.
“We found that our study species, the American Redstart, can migrate up to 43% faster to reach its breeding grounds after delaying departure from wintering grounds in Jamaica by up to 10 days,” said said lead author Bryant Dossman. He led the study while a graduate student at Cornell and is currently a postdoctoral fellow at Georgetown. “But the increase in migration speed also resulted in a more than 6% drop in their overall survival rate.”
Tactics to speed up migration can include flying faster and fewer or shorter stopovers to refuel along the way. Although faster migration helps compensate for delayed departures, it cannot fully make up for lost time. Typically, for a 10-day delay, Dossman says individuals can recover about 60% of lost time, but that still means arriving late at breeding grounds.
American Redstart spring migration routes from Jamaica 2016-2022. Credit: Motus Wildlife Tracking System
Jamaica has become increasingly drier in recent decades and that translates to fewer bugs, the mainstay of the redstart diet. Now it takes birds longer to prepare for the rigors of migration, especially from lower quality habitats. At the same time, plants are greening and insects are coming out to breeding grounds earlier, also due to climate change.
“On average, migrating songbirds only live a year or two, so keeping a tight schedule is essential. They will only have one or two chances to breed,” Dossman said. “Birds that live longer are less likely to take the risk of accelerating migrations because they have a greater chance throughout their life to reproduce and pass on their genes.”
The study is based on 33 years of data on American redstart migration departures from Fort Hill Nature Reserve in Jamaica. Co-lead author Peter Marra, director of Earth Commons – Georgetown University’s Institute for Environment and Sustainability – oversees the study site. Using this historical data in tandem with automated radio tracking and light level beacons, scientists compared the Redstarts’ predicted departure date with their actual departure date over the past few years to see how that has changed.
“The behavioral changes documented in this research remind us that how climate change affects animals can be subtle and, in some cases, can only be detected after long-term study,” says Amanda Rodewald, co- author of the study. article as well as Professor Garvin and Senior Director of the Center for Avian Population Studies at Cornell Lab.
“Understanding how animals can compensate is an important part of understanding where climate change impacts will occur,” Marra said. “In this case, we may not lose a species entirely, but it is possible that populations of some species will disappear locally due to climate change.”
What happens on redstart wintering grounds extends into the breeding season. Although the redstart population is stable and increasing across much of its breeding range, detailed eBird Trend maps show the species is declining in the northeastern United States and southern Quebec. , in Canada.
“The good news is that birds are able to react to changes in their environment,” Dossman said. “They have some flexibility and variation in their behaviors to begin with, but the question is, have they reached the limit of their ability to respond to climate change?”
Funding for the research was provided by the Cornell Lab of Ornithology, the Smithsonian Institute, and the National Science Foundation. Thanks to the Cornell Lab of Ornithology for providing this news.
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