Domestic waste disposal sites secure food availability but diminish plasma antioxidants in Egyptian vulture

Some domestic waste disposal sites (DWDS) accumulate enormous amounts of food that humans discard. This food resource is exploited by different species whose population dynamics have as a result been altered. The effects of feeding on human waste on individual health parameters such as body condition are still unknown. Traditionally, body condition in wildlife has been assessed using morphological indices based on size and weight. Expanding the range of indices to include the analysis of indicators at the physiological level can provide a more comprehensive picture of the animals' health status. In this work, we studied how different amounts of waste consumption (assessed using stable isotope analysis) affect nestling health and body condition in an expanding population of the endangered Egyptian Vulture (Neophron percnopterus). We used morphometric and physiological approaches, including plasma biochemistry, antioxidant defences and oxidative stress biomarkers. The results of the multivariate redundancy analysis and variance partitioning showed that the proportion of diet originating from DWDS is the main factor explaining physiological indicators in the studied vulture population. Nestlings that were fed on food from DWDS had lower levels of vitamins (e.g. α-tocopherol) and carotenoids (zeaxanthin and lutein), which have important functions as antioxidant defences, immunostimulant properties and ornamental purposes. Nevertheless, nestlings that were fed on food from DWDS were better nourished and experienced fewer food shortages than individuals not fed using this resource, which had lower levels of cholesterol. Possibly due to the easy access to food, breeding pairs using DWDS could have fewer difficulties in feeding their nestlings and thus could engender more regular brood sizes than those not exploiting this type of resource. Our integrative approach using diverse components was crucial for a reliable assessment of health and body condition in Egyptian Vulture nestlings and its relationship to the consumption of food derived from human-altered environments.
This study was financed by University of Barcelona (J. R., A. H. M. and H. T.), and Red Electrica de España-SA and we are grateful to Mercedes Gil. H.T was supported by a predoctoral grant from the IRBIO-University of Barcelona (APIF 2014).