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Hi everyone, I thought some of you might be interested in reading this very brief summary of a paper published in The Auk: Ornithological Advances. Migration is tough, and birds do everything they can to optimize it. How do factors like weather and experience affect the strategies they choose? A new study from The Auk: Ornithological Advances shows that older, more experienced Golden Eagles migrate in poorer weather conditions, but for a good reason -- they're timing their efforts around raising the next generation of eagles. Adrian Rus of Boise State University (now at Australia's University of Sydney), Todd Katzner of the USGS, and their colleagues studied GPS telemetry tracks to evaluate the migratory performance of almost 90 Golden Eagles in eastern North America and determine how performance related to season, age, and weather. Unsurprisingly, eagles flew faster and farther when they had strong tailwinds and thermals to help them along. What was counterintuitive, however, was that older eagles did not cover more ground than younger eagles in good weather despite their greater experience. Instead, older eagles migrated in poorer weather conditions and travelled more slowly. [The slow and steady wins the race approach - Lance] The researchers believe this is because older birds face different pressures than younger birds. Even if the weather is bad and will slow them down, they need to start heading north earlier than young birds that aren't breeding, because they have to get back to their breeding grounds in time to reclaim their territories and start nesting. "Younger eagles just need to survive the summer, so they can be choosy about when they travel north and only migrate when conditions are really ideal for fast soaring flight," explains Katzner. Adrian I. Rus, Adam E. Duerr, Tricia A. Miller, James R. Belthoff, and Todd E. Katzner (2017) Counterintuitive roles of experience and weather on migratory performance: The Auk 134(3):485-497. It would be interesting to hear if anyone has noticed if the ratio of adult to young Bald Eagles changes noticeably at Sheffield Mills as spring approaches. All the best, Lance Lance Laviolette Glen Robertson, Ontario
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