The effects of ecology and behaviour on the evolution of colouration in Coraciiformes

What drives the evolution of plumage colour in birds? Bird colour is
likely to be under both natural and sexual selection where natural
selection may favour evolution towards crypsis or camouflage whereas
sexual selection may favour evolution towards conspicuousness. The
responses to selection are predicted to relate to species’ ecology,
behaviour, and life history. Key hypotheses have focused on habitat and
light environment, breeding strategy, territoriality, and hunting
behaviour. We tested these potential causes of colour variation in the
Coraciiformes, a colourful clade of non-passerine birds, using
phylogenetic comparative methods and data on plumage colouration and
brightness measured from museum specimens. We found that correlates of
colour evolution in Coraciiformes vary across body regions and depend on
the focal colour property (hue or brightness). While light environment
showed widespread effects on colouration in multiple body regions for both
hue and brightness, selection pressures related to behavioural
characteristics had more spatially localized effects (e.g. territoriality
on wing feather brightness and hunting strategy on belly hue). Our results
reveal both general patterns that may hold across other bird clades and
more nuanced effects of selection that are likely to be mediated through
the visual ecology of the signaller and receiver and the behavioural
characteristics of Coraciiform species.