Abstract
Animal coloration is key in natural and sexual selection,
playing significant roles in intra- and interspecific communication because of
its linkage to individual behaviour, genetics and physiology. Simple animal
traits such as the area or the colour intensity of homogeneous patches have
been profusely studied. More complex patterns are widespread in nature, but
they escape our understanding because their variation is difficult to capture
effectively by standard, simple measures. Here, we used fractal geometry to
quantify inter-individual variation in the expression of a complex plumage
trait, the heterogeneous black bib of the red-legged partridge (Alectoris
rufa). We show that a higher bib fractal dimension (FD) predicted better
individual body condition, as well as immune responsiveness, which is
condition-dependent in our study species. Moreover, when food intake was
experimentally reduced during moult as a means to reduce body condition, the
bib's FD significantly decreased. Fractal geometry therefore provides new
opportunities for the study of complex animal colour patterns and their roles
in animal communication.