Our friend at the Smithsonian Migratory Bird Center, Nathan Cooper, continues to make news with his various studies on the movements of Kirtland's Warblers on the landscape of both the breeding grounds and wintering grounds -- and now on everything in between.
A story published on Oct. 4 on the website of the SMBC features Cooper's latest research on KW movements, focusing on the impacts of particularly dry winters on the wintering grounds in The Bahamas and across the Caribbean. We knew that dry winters had a carry-over effect on nesting season -- that adults were less successful in raising young in the summers following dry winters. But Dr. Cooper's new research shows that dry winters have an impact in a different way: higher rates of mortality during spring migration.
We knew from earlier research that birds that arrive on the nesting grounds after dry winters are less healthy because they are carrying less fat. They need to spend more time gathering food for themselves, which means they have less time to dedicate to gathering food for their young. The result is fewer hatchlings successfully fledge.
But Dr. Cooper's research shows that those same birds that are carrying less fat when they decide to leave the wintering grounds are also more likely to perish on their migration. According to the Smithsonian's website, "The team analyzed three years of radio tracking data from 136 tagged (with radio transmitters) Kirtland’s warblers to estimate their survival rate across their migration and its relation to environmental factors."
This research is the result of a grant from the U.S Fish and Wildlife Service’s Great Lakes Restoration Act "to build full annual-cycle population models for Kirtland’s warblers." Building this model will help the Conservation Team identify specific dangers involved in migrations and potentially work to mitigate some of them. According to the Smithsonian's story, this model will help scientists determine how the dangers of migration fit into the broader picture for warblers. That information is potentially useful for the conservation of other declining migratory species.
You can read more here: https://nationalzoo.si.edu/.../drier-winter-habitat...
Cooper's study was published in the Oct. 4 issue of "Current Biology." (It's behind a paywall. Sorry.) https://www.cell.com/curre.../abstract/S0960-9822(24)01225-9
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