The effect of food quality on breeding strategy in Griffon vultures (Gyps spp.)



Griffon vultures feed from the soft tissues of large mammal carcasses: a diet which contains very little calcium. Comparatively large amounts of calcium are required in order to breed, first for eggshell formation and then for bone mineralization of the chick. These requirements are estimated. Adults were not found to supply the chick with a mineral-rich crop secretion during rearing, but they must feed the young with calcium-rich food items, such as bone fragments. These are not abundant, and it is suggested that the mineral requirements for breeding have determined certain features of the breeding strategy in these birds—such as laying a single egg and having a prolonged rearing period.