Age identification of Eurasian Griffon Vultures Gyps fulvus in the field

Abstract

Griffon Vultures Gyps fulvus are notoriously difficult to age precisely, given their delayed maturity and large inter-individual variation. However assessing the age of young individuals can be important for studies dealing with behaviour, population dynamics and conservation. Using a large sample of individually marked Griffon Vultures of known age in southern France, we studied changes with age of morphological parameters observable at distance on the ground. Combining features of bill colour, eye colour, shape and colour of neck ruff feathers and shape of upperwing greater coverts, it was possible to attribute age classes with a precision of c 2 years. The first characteristics to change were the colour of the bill, with the front of the bill getting clear before the sides of the bill, and the shape of the greater coverts, where pointed juvenile feathers were replaced by paler and more rounded feathers. In the second year, the ruff turned progressively paler and shorter to become adult-like in the seventh year for most individuals. The eye turned lighter only in the fifth year. Males tended to acquire adult plumages more rapidly than females.