Do agricultural environments increase the reproductive success of White Stork Ciconia ciconia populations in South-Western Poland?

Abstract As populations of White Stork Ciconia ciconia have decreased at different rates in Europe, the specific environmental drivers that influence breeding success are a matter of controversy. Here we use body size, blood, and environmental data of a total of 1226 stork nestlings of different ages from a total of 363 nests in three different habitats (meadows, forest-edges, open agricultural landscapes) in S-W Poland to ask whether: 1) natural grassland environments increase the reproductive output in comparison with agricultural landscapes, 2) nestlings from agricultural landscapes differ in health status from nestlings in more natural habitats, 3) differences in environmental stress translate into respective differences in reproductive output and health status of nestlings. There was no significant difference in age corrected body mass and in the temporal increase in nestling mass between the study sites. Clutch sizes were highest and age corrected total clutch mass lowest at the meadow sites while agricultural and woodland sites did not significantly differ. Hemoglobin and red blood cell content were lowest and white blood cell and blood antioxidant concentrations were highest in the meadows indicating higher degrees of environmental stressors. These blood parameters varied strongly among study years. Our study does not confirm that agricultural landscapes are less suited for stork breeding success. We even find some indication of a better health status of nestlings in agricultural environments that might compensate smaller clutch sizes. Our data indicate that reproductive output is multifaceted. As we found some indication of a trade-off between clutch size and health status we argue that only multiple metrics of reproductive success are able to assess the long-term effect of habitat choice on fitness.