Inclement weather interacts with agricultural intensity at landscape scales to reduce reproductive success in an at-risk aerial insectivore

Abstract Emerging evidence indicates that associations between landscape contexts and population change may vary with prevailing weather conditions. Agricultural landscapes are often more homogeneous, receive greater agrochemical inputs, and support altered or reduced insect prey communities, influencing buffering capacity during challenging conditions. Because weather can constrain avian thermoregulation, alter foraging patterns, and insect availability, associations between agricultural intensity and aerial insectivore fitness may vary in magnitude and direction under different weather conditions. We therefore evaluate whether the relationship between row-crop cover and fitness varies with weather across breeding attempts. We paired a 13-yr dataset of Hirundo rustica (Barn Swallow) clutch size, hatching ratio, and fledging success, gathered across a gradient of agricultural intensity in southwestern Ontario, Canada, with historical weather conditions collected during periods relevant to each parameter of reproductive success. We used this dataset to test the hypothesis that the relationship between agricultural intensity and the outcome of a breeding attempt may be modulated by the experienced weather conditions. Our analyses treated first and second breeding attempts separately. For first attempts, temperature modified the association between agricultural intensity and both hatching and fledging success, and precipitation modified the association for fledging success only. Interactions were not supported for clutch size in either attempt or for hatching in second attempts. Together, these results indicate that the effects of agricultural intensity on reproduction likely depends on prevailing weather conditions, and the stage of the breeding season. Considering projected increases in heat extremes and heavy rainfall, this context dependence suggests that climate change may alter, and in some cases intensify, the demographic consequences of intensive agriculture.