Arthropod prey and diets of woodland migrants are similar between natural riparian woodlands and anthropogenic woodlots in the northern prairie region

Migration is an energetically expensive activity with important links to population dynamics of migratory birds. Identification of high-quality stopover habitat to support migratory refueling is, therefore, important for woodland migrant conservation. Woodland habitat is scarce in the northern prairie region, consisting of natural riparian corridor woodlands (corridors) and anthropogenic woodlots (woodlots), but supports large numbers of migrant birds during stopover. To assess prey abundance, diet composition, and effects of prey abundance on the energetic condition of insectivorous migrant landbirds at corridors and woodlots in the northern prairie region, we sampled arthropods from the two habitats and collected fecal samples to ascertain migrant bird diets during spring and fall migrations. We found that standardized arthropod counts and biomass from all sampling methods showed no consistent differences between corridors and woodlots in either season. Araneae, Coleoptera, Hemiptera, Diptera, and Hymenoptera were the dominant arthropod taxa in both seasons for both habitats. Migrant diets contained large proportions of Coleoptera, Diptera, and Hemiptera in fall and Hymenoptera, Coleoptera, and Diptera in spring at both habitats. Dietary analyses of percentage biomass revealed different patterns, with Lepidoptera highest in both seasons. Annual differences in arthropod counts and biomass were evident for both seasons, with lower counts and biomass in fall 2011 than in fall 2010 and in spring 2011 than in springs of 2010 and 2012. Only arthropods collected by sticky traps were positively correlated with plasma metabolites associated with refueling rates, and habitat type was not a significant predictor of plasma metabolite levels. These data collectively suggest that arthropods were present in sufficient abundance and diversity at both corridors and woodlots for migrant birds to successfully refuel at these riparian stopover sites.