Sex, size and eco-geographic factors affect the feeding ecology of the Iberian adder, Vipera seoanei

Numerous dietary studies have shown that European vipers (genus Vipera) present low feeding frequency and a specialist diet, which is characterised by a marked ontogenetic shift. However, how eco-geographic factors shape species' feeding ecology remains scarcely addressed. We investigated the feeding ecology of the Iberian adder, Vipera seoanei, examining 402 specimens distributed across its distributional range and addressing how biological, temporal and eco-geographic factors relate to the species feeding activity and dietary consumption. Our results indicated a low feeding frequency in the species, higher in juveniles than in adults. Adult females showed higher rates of prey consumption than adult males, which match to the distinct reproductive demands of both sexes, although no differences between reproductive and non-reproductive females were found. V. seoanei preyed on a varied taxa spectrum, but showed a rather specialist diet based on small mammals. Amphibians and reptiles were also an important part of its diet, particularly in the juveniles. Body size was found as the single biological trait related to the consumption of major prey groups, supporting the occurrence of an ontogenetic shift in the diet. Two habitat and two climatic factors correlated to the consumption of major prey groups, reflecting the ecological requirements of prey across the viper's range. Overall, this study extends the existing knowledge on the feeding ecology of European vipers, signalling how energy intake and allometric constraints shape the feeding activity and dietary consumption of the species across the geography, leading to distinct feeding strategies in juveniles and adults.