Breeding performance of an aerial insectivorous bird under contrasting farming systems

Over the past decades, intensive agriculture has expanded worldwide in response to the rising human demand for food. Intensive farming practices commonly involve the application of pesticides and other agrochemical compounds, contributing to the global decline in farmland bird populations, particularly aerial insectivores. Moreover, the increased mechanization of agricultural operations (e.g., grass cutting, tree pruning, and brush chipping) may destroy nests and reduce the breeding success of ground-nesting bird species. Here, we used a ground-nesting insectivorous bird, the Red-necked Nightjar (Caprimulgus ruficollis), as a model to test for the effects of organic vs. intensive farming practices on breeding performance. We used data from 191 nightjar nests monitored over a 4-year period in a highly cultivated landscape of SE Spain. Four breeding parameters (clutch size, hatching success, fledging success, and overall breeding success) were compared between two adjacent farms under organic and conventional intensive management. Additionally, we compared four population-level attributes (breeding phenology, breeding density, age structure of breeders, and foraging range size) considered to be important determinants of breeding performance. Nightjars breeding in the organic and in the intensive farms had a moderate breeding performance comparable to that reported in other, more extensive agricultural landscapes (e.g., vineyards). All breeding parameters and two out of the four measured population-level attributes were statistically not different between the organic and the intensive farm. However, nest aggregation was higher in the organic farm, and space use analyses revealed that GPS-tracked nightjars nesting within the intensive farm traveled to foraging areas outside the farm more often than those from the organic farm. This suggests that plasticity in foraging behavior (e.g., the use of alternative foraging sites) may buffer the potential negative effects of intensive farming practices (e.g., decreased prey availability) on the breeding performance of nightjars. Our study underlines the potential role of landscape complementation and ecological plasticity in space-use behaviors as determinants of breeding performance in farmland birds, enabling these species to (partly) compensate for the impacts of intensive agriculture.