Birds breed better when they ‘float’ through bad times

[Cara J]

Many bird populations include perplexing young males who choose not to settle down and breed.  Instead, they “float” through the breeding season without a territory. But this unattached approach may benefit birds in tough times. Biologists examining imperiled southwestern willow flycatchers (Empidonax traillii extimus) in Arizona recently found that these “floaters” survive and reproduce more than breeding birds in the aftermath of major drought. “Floaters tend to move around not showing territorial behaviors, so they’re hard to study,” said Tad Theimer, lead author on the paper published in The Auk: Ornithological Advances. “We were setting up nets throughout the year and would catch these birds we never saw acting territorially, so we knew they were in the habitat but weren’t breeding. That gave us the opportunity to get a window on this little-known secretive ‘underworld’ of bird society.” Listed as endangered in 1995, southwestern willow flycatchers inhabit rare riverine forests that are disappearing due to activities like damming and farming. In a cooperative study between the Bureau of Reclamation, U.S. Geological Survey and Arizona Game and Fish Department, researchers set up study areas near central Arizona’s Roosevelt Reservoir and the San Pedro and Gila rivers, where they caught 1,000 flycatchers [...]

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