Livestock farming practices modulate vulture diet-disease interactions

Abstract

Low- and high-intensity farming exert different direct and indirect effects on vulture populations by driving the availability, exploitation and characteristics of carrion. This is especially true for the levels of pharmaceuticals in wild and domestic animal carcasses. However, the impact of farming systems on the diet-related health of avian scavengers remains unclear. Here, we evaluate diet and disease signs in nestlings of three European species of vultures (Cinereous, Aegypius monachus, Griffon, Gyps fulvus, and Egyptian, Neophron percnopterus), living in different regions of Spain under contrasting farming schemes. We test the hypothesis that disease (oral mucosal lesions caused by mixed fungal and bacterial infections) in vultures is influenced by features of food and foraging conditions derived from farming systems, especially due to the expected chronic and irregular ingestion of pharmaceuticals under intensive (factory farms) compared to extensive systems. A large proportion of nestlings of the three vulture species in central Spain (high-intensity farming area) continue to be affected by oral lesions (cinereous: 75%, n = 16; griffon: 61%, n = 28; Egyptian: 46%, n = 13). The same type of lesions, at a much lower frequency, was found in nestling of the three vulture species in each of the selected areas corresponding to low-intensity farming areas in southern and northern Spain (Cinereous: 39%, n = 13; Griffon: 7%, n = 14; Egyptian: 6%, n = 17). As predicted, a positive relationship was found between the proportion of nestlings with lesions and the frequency of intensive livestock from factory farms (swine and poultry) in the diet. The intensive medication in factory farms deserves further research to assess its implications in vulture diet-disease interactions at large geographical scales. Assessing the presence of oral lesions as an indicator of physiological alterations is encouraged along with pharmacovigilance in surveillance programs aimed at evaluating the direct and indirect effects of livestock farming practices on vulture health. Given the increasing exploitation of domestic instead of wild animals by vultures, the growth in high-intensity farming and the medication practices in free-ranging and semi-extensive farming systems, this assessment would help to characterize the risks associated with different farming operations for wildlife. This evaluation is crucial to avoid exacerbating the detrimental consequences of supplementary feeding programs contrary to their primary aim of the conservation of endangered species.