Factors Affecting the Relationship between Body Mass and Age in the Izard

We investigated the influence of gender, capture period, and between-year variation on the relationship between body mass and age in the izard ( Rupicapra pyrenaica ) using data obtained on 201 individuals captured in a Pyrenean reserve, France. Body mass was measured in spring or autumn 1984–1993. Absence of sexual dimorphism in body mass probably resulted from the high density of this protected population. Strong quadratic relationships between age and body mass were observed for spring and autumn ( r 2 = 0.79 and 0.76, respectively). Izards exhibit lower body mass in spring than in the previous autumn irrespective of age class. No significant between-year variation occurred in body mass in autumn. There were marked differences between years in spring that may be related to previous climatic conditions in winter, particularly daily temperature in December and total snowfall from November to April.