Diet is not related to productivity but to territory occupancy in a declining population of Egyptian VulturesNeophron percnopterus

Abstract

SummaryA prominent threat to European vultures has been sanitary regulations that banned the disposal of livestock carcasses. Changes in food abundance following these regulations have been associated with changes in vulture behaviour and demographic parameters, but to what extent diet changes are responsible for population declines is poorly understood. The Egyptian VultureNeophron percnopterusis the smallest and most threatened European vulture species and has an opportunistic and diverse diet. In Eastern Europe, the Egyptian Vulture population is declining more rapidly than elsewhere but there is little information on diet composition and the relationship between diet and demographic parameters to inform conservation management. We examined whether Egyptian Vulture population declines in Bulgaria and Greece may have been associated with diet changes that affected breeding productivity by monitoring breeding success and collecting diet remains from 143 Egyptian Vulture breeding attempts between 2006 and 2013. We found no relationship between diet diversity or composition and productivity. However, there was a significant relationship between occupancy rate of territories and diet diversity, indicating that occupancy rate decreased with a very diverse or a very narrow diet and a higher proportion of wild animals or a lower proportion of livestock in the diet. There was no temporal change in diet diversity in Bulgaria after admission to the EU in 2007. We conclude that it is unlikely that diet limitations on reproductive output are a critical threat to Egyptian Vultures on the Balkan Peninsula. The relationship between diet diversity and territory occupancy rate may indicate that adult birds with a very narrow or a very broad diet may be more susceptible to consuming poisoned carcasses, and more information on the effect of diet availability on adult and juvenile survival would be useful to inform and improve conservation management actions.