Data_Schneider_Owl.xlsx

Interspecific competition profoundly influence the ecology of species and climate change is expected to alter the strength of interspecific interactions. However, there is a significant gap in our understanding about the manifestation of such combined effects. Using long-term data from sympatric breeding populations of the barn owl (<i>Tyto alba</i>) and the tawny owl (<i>Strix aluco</i>) in southern Hungary, we explored the associations between the owl species’ (i) breeding phenology (annual median laying dates), regional weather components (daily precipitation, temperature minimum and maximum), and (ii) reproductive characteristics (laying date, clutch size, fledgling number) and the co-occurence of the two species in the same nestbox in the same breeding season. In the barn owl, breeding onset was associated with daily temperature maximum, and advanced by two weeks in the study period, while the tawny owl breeding onset did not change. We found that when the two species used the same nestbox, the breeding of barn owl was delayed by five weeks, and they produced one more egg and owlet in average, but second breedings were practically absent. In contrast, the tawny owl's breeding started one week earlier upon using the same box, also with increased clutch size, although this did not manifest in the number of fledglings. Our results imply that climate change will intensify the nest site competition between the two species with their breeding onsets getting closer. Considering that nest site competition already triggers costly compensatory mechanisms for both species (suboptimal breeding onset, increased allocation into reproduction) and direct reproductive costs for the barn owl (lost opportunity for second breeding), the climate change-induced intensification of nest site competition might lead to population declines.