Overgrazing triggers cascading effects on a top avian scavenger: long-term changes in diet and breeding success

Abstract Wildlife feeding and nutrition are key drivers of several demographic parameters, such as breeding success and survival, influencing long-term population viability. To comply with the diet requirements that ensure offspring survival, parents adapt their forage strategies to the environmental conditions and resource availability. This is especially important for central-place foragers like raptors, where prey availability in the surroundings of nest and livestock carcasses significantly impact both foraging efforts and breeding success. Here we take advantage of 20 years extensive monitoring (2001–2020) of the Canarian Egyptian vulture ( Neophron percnopterus majorensis ) on the Fuerteventura Island (Canary Islands, Spain) to assess (1) what factors drive vulture diet diversity and, (2) how the number of livestock and diet diversity coupled together with environmental conditions affect breeding success and, ultimately, the conservation of vulture populations. We identified 3,787 prey items belonging to 37 different species. Diet diversity was positively related to the number of wild prey and to low livestock grazing pressure periods. Breeding success was positively related to the number of wild prey, low herbivory pressure and, to a lesser extent, to diet diversity. These results demonstrate the importance of wild prey on Canarian Egyptian vulture’s diet, albeit livestock carcasses are the most abundant feeding resource. We argue that livestock have controversial conservation implications for this species because it provides a stable feeding resource, but, in turn, is one of the major ecosystem disruptors. Overgrazing by livestock can negatively affect wild primary consumers, which are essential for this endemic vulture population.