[EN]: Secondary sexual traits may have evolved to inform about individual quality. Individuals of primer quality are expected to have benefits in intra- and inter-sexual interactions and ultimately in fitness. However, the covariation of the expression of sexual traits and individual fitness as individuals age is still poorly known and controversial. Within a life-history perspective, ornament expression is expected to increase as individuals age, despite decreasing their residual reproductive value. Nevertheless, environmental conditions may also drive both reproduction and the expression of phenotypes throughout their lives. However, little is known about the environmental influence on age-dependence variation of sexual traits. Based on the analysis of a 10-year individual data set of adult common kestrels (Falco tinnunculus), we study 1) the age-dependence of the number and size of back spots, a melanin-pigmented and sexual trait in adult males; and 2) the environmental influence on the expression of these traits as individual age. We considered vole abundance during the length of the study period as proxy of environmental variation. We decomposed age-related changes into within and between individual variation to assess their contribution to population-level patterns. Our results showed a within-individual decrease of the number but not size of back spots. Instead, size but not number of back spots was positively associated with food availability. In addition, reproductive performance increases as individuals age. We suggest that the number of back spots can be an age indicator and perhaps an index of reproductive quality and size of back spot reflects the environmental conditions at the time of moulting. Our results suggest that genetic and environmental factors may explain the expression of different characteristics of a same trait.

Trabajo presentado al XXII Congreso Español de Ornitología: "Aves y ser humano: una relación variable", celebrado en Madrid del 6 al 9 de diciembre del 2014.

Peer reviewed