Recent research has challenged a fundamental assumption about bird migration, revealing that escaping to warmer climates during the winter doesn't actually save birds energy.
The research, which utilized cutting-edge miniaturized logging devices, provides unprecedented insights into the physiological costs of migration.
For the first time, scientists have continuously tracked the heart rate and body temperature of wild blackbirds throughout their entire migration period, measuring these vital signs every 30 minutes from fall to spring.
The findings overturn the long-held belief that birds conserve energy by migrating to warmer regions.
"We never expected to discover that birds gain no overall energy advantage by escaping cold winters," Nils Linek, a first author of the study and a researcher at the Max Planck Institute of Animal Behavior, said in a statement.
"It was a longstanding textbook assumption that animals spend less energy by migrating to warmer places, but our findings have shown that these savings don't add up."
The research team surgically implanted sophisticated sensors into 120 wild blackbirds in southern Germany, where some birds migrate south to Spain and France while others remain resident year-round. These devices collected approximately 1 million data points, offering an unprecedented window into the physiological demands of migration.
One surprising discovery was that migrating blackbirds employ a previously unknown energy-saving strategy: they decrease their metabolism three weeks before departure by "turning down their internal thermostat," Linek said.
However, this preparation for migration doesn't translate into overall energy savings during their winter stay in warmer climates.
"This was not what we anticipated," Scott Yanco, co-first author on the study from the Yale Center for Biodiversity and Global Change, said in a statement. "The energy modeling we did in the study predicted that migration should definitely create an energy surplus because of the substantially reduced cost of keeping warm in milder climates."
The researchers suggest that hidden costs might offset any thermal advantages gained from wintering in warmer regions. These could include increased vigilance needed in unfamiliar environments, immune system demands, or other unknown stressors.
Linek added, "We can only speculate at this point, but we suggest that there may be other physiological adaptations or hidden costs that migrant blackbirds face in their milder overwintering sites."
The study's implications extend beyond just understanding bird behavior. "Understanding the physiological underpinnings of migration means that we can better forecast which species may adapt, which may alter their migratory patterns, and which may face greater risks as the world continues to warm," Jesko Partecke, senior author and a group leader at the Planck institute, who has studied blackbird migration for two decades, said in a statement.
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Reference
Linek, N., Yanco, S. W., Volkmer, T., Zuñiga, D., Wikelski, M., & Partecke, J. (2024). Migratory lifestyle carries no added overall energy cost in a partial migratory songbird. Nature Ecology & Evolution. https://doi.org/10.1038/s41559-024-02545-y
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