Diet and feeding habits of nesting and non-nesting ravens (corvus corax) on a mediterranean island (vulcano, eolian archipelago)

The almost complete absence of information on the trophic ecology of Corvus corax for Mediterranean areas prompted the present research on the small island of Vulcano. Focal observations allowed us to survey the population, which is divided into four territorial pairs and one non-nesting flock (mean n = 23.6 ± 16.3). This flock roosted preferentially near a rubbish dump. Ravens on Vulcano proved to be omnivorous and to feed upon a wide range of food items, with the differences in diet found to be more quantitative than qualitative and related to the season and to the social system. The flock birds consumed more vegetable matter, carrion of domestic animals, other organic matter (eggshells, fish and birds) and rubbish than the pairs. They live in a restricted volcanic area, some 6 km2, unsuitable for predation and therefore show a more pronounced scavenging strategy, also travelling to neighbouring islands to feed at other dumps. The pairs have access to unlimited food resources, i.e., Rattus rattus and Oryctolagus cuniculus; as proved by field estimation of those mammal populations. Ravens highly select for black rats (Bi = 0.75) and include more food items related to predation in their diets. The frequency of black rats exploited by pairs (38.7%) is the highest so far recorded over the entire species' range. The diet of the pairs has a more marked seasonal fluctuation than that of the flock. © 2003 Taylor & Francis Group, LLC.