Habitat degradation caused by climate change is wreaking havoc with bird migration dates. According to a new study, birds may partially compensate for these changes by delaying the start of spring migration and completing the journey more quickly. Still, the method has a cost a reduction in overall survival.
The findings of researchers from Cornell University, the 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 nesting grounds after delaying departure from wintering grounds in Jamaica by up to 10 days,” said lead author Bryant Dossman.
Tactics to speed up migration may include flying faster and making fewer or shorter refueling stops along the way. While faster migration helps compensate for delayed departures, it cannot completely make up for lost time. In general, for a 10-day delay, Dossman says individuals can recover about 60% of the lost time, but that means they’re still arriving late to the breeding grounds.
Jamaica has become increasingly arid in recent decades, which translates into fewer insects that are a mainstay of the kingfisher’s diet. It now takes longer for birds to get fit for the difficult migration, especially from lower quality habitat. At the same time, plants are turning green and insects are climbing earlier to nest – also due to climate change.
Migratory warblers only live a year or two on average
“Migratory warblers only live a year or two on average, so it’s important to keep a tight schedule. They only get one or two opportunities to breed,” Dossman said. “Longer birds are less likely to risk accelerating migration because they have more chances to reproduce and pass on their genes during their lifetime.”
The study is based on 33 years of data on American Redstart migration at Fort Hill Nature Reserve in Jamaica. Senior co-author Peter Marra, director of the Institute for Environment and Sustainability at Earth Commons – Georgetown University – is overseeing the study site. Using this historical data in tandem with automated radio tracking and light-level markers, the researchers compared the robins’ expected departure date with their actual departure date in recent years to see how it has changed.
“The behavioral shifts documented in this research remind us that the way climate change affects animals can be subtle and in some cases can only be detected after a long-term study,” said Amanda Rodewald, co-author of the paper. as well as Professor Garvin and Senior Director of the Center for Bird Population Studies at Cornell Lab.
“Understanding how animals can compensate is an important part of understanding where the impacts of climate change will occur,” Marra said. “In this case, we may not lose the species completely, but it is possible that populations of some species may become extinct locally due to climate change.”
What happens in the wintering grounds of the heron carries over into the breeding season. Although the redstart population is stable and breeding in most areas, eBird Trend’s detailed maps show that the species is declining in the northeastern United States and southern Quebec, Canada.
“The good news is that birds are able to respond to changes in their environment,” Dossman said. “They have some flexibility and variation in their behavior to begin with, but the question is, have they reached the limit of their ability to respond to climate change?”
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