Differential predation upon sex and age classes of tuco-tucos (Ctenomys talarum, Rodentia : Octodontidae) by owls

Predation by burrowing (Athene cunicularia) and short-eared (Asio flammeus) owls upon sexes and age-classes of the subterranean herbivorous rodent Cte nomys talarum were studied by comparing characteristics of field-trapped an d preyed-upon individuals. Owls took a greater proportion of mates than fem ales in comparison with their respective field densities. This sex-biased p attern of predation was most marked during the breeding season of C talarum and mainly affected subadult mates. A set of ecological features of C tala rum, such as food habits and above ground mobility, that might explain diff erential vulnerability by sex was analysed and did not support the observed pattern. We suggest that it is determined by higher above ground exposure of subadult males during the breeding season because they interact above gr ound with adult males and search for settlement sites to establish their ow n burrows.