Date: April 5, 2017
Source: American Ornithological
Society Publications Office
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 actually migrate in
poorer weather conditions and cover less ground than their younger
counterparts, 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 despite their greater experience.
Instead, older eagles migrated in poorer weather conditions and travelled more
slowly.
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.
Lead author Adrian Rus, who
worked on the study as an undergraduate, enjoyed the challenges involved in
analyzing the migration data. "The best part about working on this project
was using specialized software to visualize the golden eagle migrations and
being able to pair it with meteorological data to answer my biological
questions," he says. "As a result, the project greatly improved my
geospatial and statistical analysis skills and was instrumental my current
graduate research in animal movement ecology."
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