Age-dependent differences in iris colouration of passerines during autumn migration in Central Europe

Michał Polakowski; Krzysztof Stępniewski; Joanna Śliwa-Dominiak; Magdalena Remisiewicz

doi:10.7717/peerj.9188

Age-dependent differences in iris colouration of passerines during autumn migration in Central Europe

PeerJ. 2020 Jun 8:8:e9188. doi: 10.7717/peerj.9188. eCollection 2020.

Authors

Michał Polakowski¹, Krzysztof Stępniewski², Joanna Śliwa-Dominiak¹, Magdalena Remisiewicz²

Affiliations

¹ Institute of Biology, University of Szczecin, Szczecin, Poland.
² Bird Migration Research Station, Faculty of Biology, University of Gdańsk, Gdańsk, Poland.

Abstract

Avian eye colour changes with age, but many aspects of this transition are still insufficiently understood. We examined if an individual's sex, age, species and body condition are related to the iris colour in common migratory passerines during their autumn passage through Central Europe. A total of 1,399 individuals from nine numerous species were ringed and examined in late autumn in northern Poland. Each individual was sexed by plumage (if possible) and assigned to one of three classes of the iris colour-typical for immatures, typical for adults and intermediate. We found that the iris was typical in 97.7% cases of immatures and in 75.8% cases of adults and this difference was significant. Species, sex and body mass index (BMI) had no significant influence on the iris colour. We show that iris colour in passerines in late autumn is strongly age-dependent and thus can serve as a reliable feature for ageing in field studies, especially in species difficult to age by plumage.

Keywords: Age determination; Autumn migration; Body mass index (BMI); Eye colour.

Grants and funding

The fieldwork and the collation of databases for this study were supported by a Special Research Facility grant (SPUB) from the Polish Ministry of Science and Higher Education to the Bird Migration Research Station, University of Gdańsk (38/E-335/SPUB/SP/2019). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.