Half century closure of a nest box project: What determines whether a Pied Flycatcher breeding in subalpine birch forest will return the next season?


What determines whether a Pied Flycatcher will return to breed in the Swedish mountains next year? Based on no less than 5,742 flycatchers studied over more than 50 years, Erik Nyholm addresses this question in a new paper in BirdLife Sweden’s research journal Ornis Svecica. The impressive dataset is collected within the environmental monitoring project LUVRE.

After their first breeding season, only 7.5% of the females returned, whereas 27% of the males did so. Among the birds that had completed two breeding seasons, however, both females and males returned at similar rates, just under 40%. If a nest was predated, most often with a small mustelid as the culprit, the chances of a female returning the next breeding season decreased, while a good year of breeding with many fledglings increased those chances. Surprisingly, the correlation was reversed in males! The proportion of returning birds decreased for females, but remained constant for males. 

As always, the research paper is freely available as Open Access, and includes a comprehensive summary in the alternative language (Swedish), which can be found in the PDF file. You can find the paper via its Digital Object Identifier (DOI) 10.34080/os.v29.20019 on our site https://os.birdlife.se.

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