Feather growth bars as a biomarker of habitat fragmentation in the Eurasian treecreeper

Habitat fragmentation poses a major threat to animal species worldwide. However, a lack of accurate and easy-to-collect biomarkers can hamper the identification of populations vulnerable to fragmentation. Ptilochronology, the measurement of growth bar length from feathers, has been shown to respond to individual nutritional status and may thus serve as a useful biomarker of habitat fragmentation in birds. We examined the influence of habitat fragmentation on feather growth bar length in the free-living Eurasian treecreeper (Certhia familiaris), an area-sensitive old-growth forest passerine breeding in boreal forests under intense management. We found no clear indication that feather growth bar length was associated with habitat fragmentation. However in young treecreepers, high amount of edge and large number of patches tended to be related to shorter growth bar length. Our results thus provide no strong support for the utility of ptilochronology as an important biomarker of habitat fragmentation in this species.