  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.
