Animal-built structures that function in mate attraction can be constrained in signal expression by
the availability of building materials in the environment and male ability to find them as well as the
ability to construct the structure itself. As part of their courtship display, male great bowerbirds
Ptilonorhynchus maculatus ...
Animal-built structures that function in mate attraction can be constrained in signal expression by
the availability of building materials in the environment and male ability to find them as well as the
ability to construct the structure itself. As part of their courtship display, male great bowerbirds
Ptilonorhynchus maculatus use hundreds of grey-white objects to create a bower court. Males
arrange these objects to create a positive size-distance gradient, the evenness of which generates a
forced perspective visual illusion that is associated with mating success. However, a range of
differently sized objects are required to build a high-quality gradient, and it is unclear how local
object availability and male ability to place objects in the correct location (i.e. building ability) affect
gradient quality. To disentangle these effects, we provided males with a standardised set of court
objects after removing their original court objects. If gradient quality is associated with male building
ability, we predicted that the quality of the gradient constructed with the standardised set of objects
would be positively correlated with the male’s original gradient quality. Contrary to our predictions,
males that built high-quality gradients in their original court did not build high-quality gradients
when given a standardised set of objects. We conclude that the bower court may not be a reliable
signal of male building ability, and that object availability and/or male ability to locate appropriate
objects explains some of the observed variation in gradient quality.
