Sex Difference in Breeding Age of Griffon Vultures (Gyps fulvus)

The age at which young birds first pair and breed is a demographic trait relevant to population dynamics and life-history strategies (Horn 1978).Many species of large raptors occasionally have been recorded breeding as subadults (Newton 1979).This seems to be linked to a shortage of breeding adults when mortality rates are high or, alternatively, to a surplus of subadults in prime breeding condition when environmental factors are especially favorable (Newton 1979).Among subadults and yearling breeders, sex ratios become female-biased in most species (Lack 1968, Newton 1979, Ferrer and Hiraldo 1991).There is, however, evidence for male-biased sex ratios of nonbreeding juveniles and adults in a wide range of avian taxa (Breitwisch 1989).