Weather-driven dynamics in a dual-migrant system: moths and bats.

Animal migrations generate large spatial and temporal fluctuations in biomass that provide a resource base for many predator-prey interactions. These interactions are often driven by continent-scale weather patterns and are difficult to study. Few studies have included migratory animals on more than a single trophic level or for periods spanning multiple entire seasons. We tracked migrations of three species of agricultural pest noctuid moths over the 2010-2012 autumn seasons as the moths travelled past a large colony of migratory Brazilian free-tailed bats (Tadarida brasiliensis) in Texas. Increases in moth abundance, mass of bats and duration of bat activity outside of the cave were correlated with passage of cold fronts over the study area and related increases in northerly wind. Moth responses to weather patterns varied among species and seasons, but overall moth abundances were low in late summer and spiked after one or more cold front passages in September and October. Changes in bat mass and behaviour appear to be consequences of bat migration, as cave use transitioned from summer maternity roost to autumn migratory stopover sites. Weather-driven migration is at considerable risk from climate change, and bat and moth responses to that change may have marked impacts on agricultural systems and bat ecosystem services.