The feeding behaviour of breeding Short-eared Owls (Asio flammeus) and relationships with communities of small mammal prey

Observation of five nesting pairs of Short-fared Owls (Asio flammeus) in a 70 km(2) area, le bassin du Drugeon, Pontarlier Plain (Haut-Doubs, France), revealed a connection between their distribution in space and time and the abundance of Common Voles (Microtus arvalis) and Water Voles (Arvicola ter restris). The birds selected sectors where the population densities of gras sland rodents were not only the highest but also the most evenly distribute d. Mean success of capture attempts (capture rate) was 32 %. Differences be tween males and between habitats (meadows, pastures, marshes) were not stat istically significant. However, number of young departing nest and capture rates achieved by the males were closely correlated (r = 0.89). It seems th erefore that, given the homogeneity of prey population, reproductive succes s was determined by male's hunting performance. Diet was studied from 192 p ellets representing 297 prey items. The search for correlations between cap ture attempts by males and the proportion of the different rodent species i n the diet of owl pairs showed that the ratios of Common Voles and Field Vo les (Microtus agrestis) were related to the males' hunting effort in the ha bitat typical of each rodent species (permanent grassland r = 0.97 and mars hland r = 0.96 respectively). The ratio of Water Voles in the diet was, how ever, correlated with the hunting effort in marshland (r = 0.96) though the species was more abundant in grassland.