Epizootics and sanitary regulations drive long-term changes in fledgling body condition of a threatened vulture

Abstract

Epizootics and deliberate changes in policies affecting the environment may affect large groups of species and the functioning of entire ecosystems. Although these effects often overlap in time, their simultaneous effect is rarely examined despite their importance as causes of current biodiversity loss. Here, based on the monitoring of an Egyptian vulture (Neophron percnopterus) population over thirty-three years (1986–2018), we increase our knowledge about the effects of anthropogenic-induced changes in food availability, both direct (sanitary policies limiting livestock carcass disposal) and indirect (a wild rabbit epizootic), on brood size and body condition of fledglings at nests. We compared the body mass of fledglings of broods with one chick (Single) and two chicks (within which we distinguished First and Second-hatched). The mass of Second-hatched chicks decreased after the plummet in rabbit populations (in the year 1990) and the regulations limiting carcass disposal (2005), reaching minimum values during the period with lowest food availability (i.e. 2005–2013). Recent sanitary legislation allowing carcass disposal by farmers coincides with a slight recovery in the observed body masses. Overall, this study shows that environmental changes of disparate origin can have synergistic effects on individual condition. Conservation of endangered vultures will require multi-targeted conservation plans aimed at ensuring nutritional requirements, in addition to detailed long-term monitoring, in order to detect obscure/masked drivers that affect body condition of fledglings.