Moult pattern in Eurasian Griffon Vultures (Gyps fulvus)

Abstract

Griffon Vultures (Gyps fulvus) moult is poorly known due to hardness to trap them; however, this process is very important for long-term soaring species. From 2013 to 2015, we studied the moult patterns of 1077 wild Griffon Vultures in Catalonia, examining the age of their feathers and testing if they moulted on demand. The moulting period lasted from April to December, ending in winter for adults and it was continuous for immatures, although it was less active in winter. Griffons needed five calendar years to become adults, but once adults; they could replace all their flight feathers in 2 years. First calendar year Griffon Vultures did not moult any feather until April of their following year. Second calendar year vultures demonstrated a stepwise moult (with several moult waves) on primary feathers. Adults showed higher intensity and higher randomness, despite they also showed a stepwise moult on primaries. On secondaries, subadults showed different moult focus. They did not show a clear moult on demand despite few of them shown alterated moults with feathers moulted around a cut feather, not following the moult wave. Adults did not show a consistent moult pattern but we think they may follow a moulting cycle alternating 5th calendar years and 6th calendar years patterns but possibly with some delays due to nutrition problems on their lives and some other alterations like loss of feathers on the battles they have when they are eating on carcasses; this could explain the asymmetry that Zuberogoitia (2013) has found on Griffon Vultures moults, and why some feathers have more probability to be moulted despite we found that moult on demand does not seem to occur in wild Griffon Vultures.