Migratory songbirds are not likely to show fidelity to molting sites

By Jared Wolfe

Linked paper: Effects of breeding and molt activity on songbird site fidelity by Luiza Figueira, Pedro Martins, C. John Ralph, Jaime L. Stephens, John D. Alexander, and Jared D. Wolfe, The Auk: Ornithological Advances

When playing at home, sports teams usually benefit from home-field advantage. A similar advantage exists among migratory birds that return to the same nesting site year after year to find familiar surroundings, food, and neighbors. The act of returning to the same site—site fidelity—has been documented in songbirds during nesting season for decades; however, what has remained a mystery is whether or not songbirds exhibit a similar site fidelity after the breeding season, during their annual molt, or replacement of feathers. Molting is energetically taxing, which means that birds need a reliable habitat with plentiful food resources and few predators. Scientists have long wondered whether this need similarly pressures birds to return to the same “home-field” molting site year after year.

For the first time, scientists have been able to determine whether migratory songbirds return to both breeding and molting sites; a necessary piece of data to help inform efforts to conserve valuable habitats for birds. In a recent study, a collaborative team of biologists from the Klamath Bird Observatory, USDA Forest Service, Mantiqueira Bird Observatory, and Michigan Technological University’s College of Forest Resources and Environmental Science used 31 years of bird banding data for 16 songbird species from northern California and southern Oregon to estimate the probability of the songbirds returning to the same site year after year to molt.

Findings from this research demonstrated that, while breeding behaviors were strongly associated with site fidelity, the fall molt was not associated with returning to a site for 15 of the study’s 16 songbird species. These results contribute to a growing body of research demonstrating that birds make small-to-large scale movements after the breeding season in search of the food resources necessary to successfully complete their fall molt. Food resources during the fall molt appear less predictable than during spring breeding season, leading to a propensity of songbirds to move and seek out new and food-rich habitats in California, Oregon, and beyond.

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