Distance to standing water is negatively correlated with invertebrate biomass, nestling feeding rate, and productivity in southwestern willow flyc atchers (empidonax traillii extimus)

The presence of standing water is often listed as an important component of southwestern willow flycatcher (Empidonax traillii extimus) habitat, but the mechanism for this relationship is poorly understood. We used field observations to test whether food availability (biomass of aerial invertebrates) and nestling provisioning rates varied with distance from standing water. We then used a longer-term data set to test whether three indices of habitat quality (nest initiation date, clutch size, and nest productivity) were higher in nests placed near standing water. We found that invertebrate biomass decreased with increasing distance to standing water, southwestern willow flycatcher parents provisioned nestlings at a higher rate as distance to water decreased, and nests within 10 m of standing water were initiated earlier and had higher clutch sizes and fledging success. These results indicate that, for some southwestern willow flycatcher populations, patterns of inundation throughout the breeding season may drive invertebrate prey availability and habitat quality.