Fractal geometry of a complex plumage trait reveals bird's quality

7 paginas, 3 figuras, 2 tables.Animal coloration is key in natural and sexual selection, playing significant\udroles in intra- and interspecific communication because of its linkage\udto individual behaviour, genetics and physiology. Simple animal traits\udsuch 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\ud(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,\udthe 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.We thank F. Sobrino and E. Dueñas for caring the birds; the “Juan de la Cierva” (JCI-2008-2059), “Ramón y Cajal” (RYC-2009-03967) programs of the Spanish Ministerio de Ciencia e Innovación (MICINN) for supporting L.P.-R and R.J., respectively; the Junta de Comunidades de Castilla-La Mancha, and MICINN for funding (projects PAI-02-006, PAI-06-0112 and CGL-2006-11823).Peer reviewe