Urbanization enhances ornament expression in a common waterbird

In birds, many components of visual communication (i.e. plumage and
non-plumage ornaments) play an important role in signaling of individual
quality. It is widely acknowledged that ornament expression may be
modulated by environmental conditions, however, it remains relatively
poorly explored whether and how urbanization affects the expression of
non-plumage ornamentation in urban dwelling-individuals. Here, we
investigated the effect of urbanization on the expression of bare-part
(non-plumage) putative ornament (i.e., the frontal shield size) across
eight populations of a common reed-nesting waterbird, the Eurasian coot
Fulica atra. Most importantly, we found robust support for the positive
effect of urbanization on shield size and its condition-dependent
character in coots. Also, long-term monitoring of a single urban
population revealed relationships between the ornament expression and nest
site selection patterns, as coots with larger shields were bold enough to
colonize more anthropogenically transformed urban sites with stronger
human disturbance and better accessibility to anthropogenic food. At the
same time, we found no support for associations between the shield size
and either nest defense behavior or reproductive performance in coots,
likely reflecting stochasticity of anthropogenic selective pressures. To
our knowledge, this study provides the first evidence for the enhanced
expression of an unpigmented non-plumage putative ornament in
urban-dwelling birds. Our results show that the effects of urbanization on
non-plumage components of quality signaling in birds may be complex and
multifaceted, and reinforces a need for further investigation focusing on
different types of ornamentation across divergent avian species.