Complex ageing of Griffon Vulture as a result of different moulting strategies in immature birds

In this post, I describe the different moulting strategies of immature Griffon Vultures that migrate to Africa to spend their first years of life compared to resident Griffon that remain in the Iberian Peninsula. Migratory birds are able to moult during more extensive periods in Africa, replacing their juvenile plumage in less than 2 years (c.3 in resident birds in Iberia). The key factors explaining the different moult timing between resident and migratory Griffons are also discussed.