Eumelanin-based colouration reflects local survival of juvenile feral pigeons in an urban pigeon house

TL;DR

This study investigates whether eumelanin-based colouration influences juvenile survival in urban feral pigeons, finding that darker juveniles have higher survival in one urban site, indicating possible selection processes.

Contribution

It provides empirical evidence linking juvenile eumelanin-based colouration to survival in urban pigeon populations, highlighting potential selection mechanisms.

Findings

Darker juvenile pigeons had higher local survival in one urban site.

No survival difference was observed among adults based on colouration.

Juvenile survival was negatively correlated with chick production.

Abstract

Urbanisation introduces deep changes in habitats, eventually creating new urban ecosystems where ecological functions are driven by human activities. The higher frequency of some phenotypes in urban vs rural/wild areas has led to the assumption that directional selection in urban habitats occurs, which may thereby favour some behavioural and physiological traits in urban animal populations compared to rural ones. However, empirical evidence of directional selection on phenotypic traits in urban areas remains scarce. In this study we tested whether eumelanin-based colouration could be linked to survival in two urban populations of the feral pigeon Columba livia. A number of studies in different cities pointed out a higher frequency of darker individuals in more urbanised areas compared to rural ones. To investigate whether directional selection through survival on this highly heritable trait could explain such patterns, we conducted mark-recapture studies on two populations of feral pigeons in highly urbanized areas. We predicted that darker coloured individuals would exhibit higher survival and/or philopatry (integrated into 'local survival') than paler coloured ones. No difference in local survival was found between adults of different colouration intensities. However, on one site, we found that darker juveniles had a higher local survival probability than light ones. Juvenile local survival on that site was also negatively correlated with the number of chicks born. This suggests the existence of colour- and/or density-dependent selection processes acting on juvenile feral pigeons in urban environments, acting through differential mortality and/or dispersal.