Urbanization alters courtship signals in male great bowerbirds

Humans have drastically altered the natural environment, impacting species that rely directly on natural resources to create signals to attract mates. Male great bowerbirds (Chlamydera nuchalis) construct bowers, which they decorate with coloured objects such as fruits and sticks. In urban areas, these decorations often include anthropogenic materials, such as glass, plastic and wire. We determined how urbanization affects the bower display of male great bowerbirds by quantifying the appearance of bower decorations in urban and rural habitats from the perspective of a female bowerbird. We found urban bowers were more highly decorated with larger decorations of greater colour variation that were usually anthropogenic materials. Notably, red decorations in urban bowers were more chromatic while green decorations were duller and less chromatic than those in rural settings. These differences in decoration appearance reflect contrasting decoration availability rather than male preference, as males in both urban and rural environments strongly preferred anthropogenic decorations to natural decorations during a choice test. These findings suggest that males in urban environments produce bigger, brighter and more salient bower displays for females compared with their rural counterparts, highlighting how urbanization is shaping complex behaviours linked to reproductive success.