Predator-prey interaction reveals local effects of high-altitude insect migration.

High-altitude nocturnal insect migrations are ubiquitous and represent significant pulses of biomass, which impact large areas and multiple trophic levels, yet are difficult to study and poorly understood. Predation on migratory insects by high-flying bats provides potential for investigating flows of migratory insects across a landscape. Brazilian free-tailed bats, Tadarida brasiliensis, provide valuable ecosystem services by consuming migratory pests, and research suggests migratory insects are an important resource to bats in autumn. We sequenced insect DNA from bat feces collected during the 2010-2012 autumn migrations of insects over southern Texas, and tested the utility of predator-prey interactions for monitoring migratory insect populations by asking: 1) how extensively do bats consume migratory insects during autumn? (2) does the prey community reflect known drivers of insect migrations, e.g. cold fronts? and (3) are migratory insects increasingly important to bats when local food resources decline in autumn? Bats consumed at least 21 species of migratory insects and 44 species of agricultural pests. Prey community richness increased with cold front passage. Bats consumed migratory moths over the entire autumn season, and the proportion of migratory moths in the bat diet increased over the course of the autumn season in all 3 years. This study confirms extensive consumption of migratory insects by bats, links patterns in prey communities to mechanisms driving insect migration, and documents a novel approach to tracking patterns of migratory insect movement. As an important resource for T. brasiliensis in autumn, migratory insects provide stabilizing effects to the local animal community.