The first evidence that migration increases songbirds’ survival during winter has been presented in the journal eLife.
The study in blackbirds, from the Max Planck Institute for Ornithology, Germany, reveals that migrants have a 16% higher chance of surviving the winter than non-migratory, or resident, birds. The findings provide a greater understanding of how migration and residency evolve in a partially migratory bird population.
“People may often hope for a white Christmas, but winter is a challenging time for animals living in seasonal environments due to cold temperatures, short days, long nights and low food availability,” says senior author Jesko Partecke, Research Scientist at the Max Planck Institute for Ornithology. “Animals have developed different strategies to cope with these conditions, including migrating to warmer climates. While previous theoretical research suggests migration should provide survival benefits to birds, there has until now been no solid evidence for this.”
To address this gap in the bird literature, Partecke and his team carried out a seven-year study in blackbirds around Radolfzell, at the western end of Lake Constance in Germany.
During each of the six-month summer periods in 2009 to 2016, the team fit small tracking devices on almost 500 blackbirds and ringed them in the traditional way. After each winter, they searched the area around Lake Constance for birds that had survived the season and returned from their wintering grounds. Automatic recording devices installed in the study area helped in showing whether a bird fitted with a radio transmitter was alive or dead, and if and when it had disappeared from the habitat.
The scientists then fed their data into a computer program and calculated the probability of survival in both the migratory and resident blackbirds. “Our figures revealed that most birds die during the winter, regardless of whether they migrate to the south or remain here,” says first author Daniel Zuñiga, Veterinarian at the Max Planck Institute for Ornithology. “However, of all the birds we were able to track, we saw that migrants had a 16% higher chance of surviving the winter than residents. This raised the question of why some blackbirds remain in residence when migration offers survival benefits.”
Previous theories suggest residency should improve reproductive performance in blackbirds, as it essentially gives these animals first choice of a limited number of prime breeding sites in the spring. The team used a mathematical model to estimate the reproductive performance of both migrant and resident blackbirds, and indeed found that residents should have at least a 61.25% higher breeding success rate than migrants.
“Altogether, our results provide important new insights on the evolution of migration in songbirds, although further studies are now needed to confirm our estimation on breeding success,” Zuñiga concludes. “Also, as many songbirds are threatened by human-induced risks along their migratory flyways, further research into how, where and why some of these birds are dying would be essential for directing future conservation efforts.”
The paper ‘Migration confers winter survival benefits in a partially migratory songbird’ can be freely accessed online at https://doi.org/10.7554/eLife.28123. Contents, including text, figures and data, are free to reuse under a CC BY 4.0 license.
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