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

Abstract

Summary1. 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. 2. 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 freetailed bats (Tadarida brasiliensis) in Texas. 3. 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. 4. 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. 5. 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.

Environmental effects on flying migrants revealed by radar

“…Inappropriate responses to environmental heterogeneity and dynamics could strongly jeopardize migrant fitness due to direct mortality or through carry-over effects that may lower reproductive output (Newton 2008). Although some important progress has been made in recent years (Krauel et al 2015, Shamoun-Baranes et al 2017, we still lack good understanding of how aerial migrants sense and respond to their dynamic habitat.…”

Ongoing changes in migration phenology and winter residency at Bracken Bat Cave

“…In either case, the decision to occupy Bracken Cave throughout the winter indicates the presence of requisite resources and environmental conditions to support overwintering. Furthermore, the steady increase in the total number of overwintering bats in Bracken Cave, as well as the increasing propensity for overwintering in this region may indicate an expanding winter range of common prey such as noctuid moths (Krauel, Westbrook, & McCracken, ; Weaver et al., ). Systematic foraging flights throughout the winter indicate year‐round presence of food sources in this region of Texas, and a modeling study supports this range expansion in the corn earworm ( Helicoverpa zea ; Diffenbaugh, Krupke, White, & Alexander, ), an important prey species and crop pest of the region (Lee & McCracken, ; McCracken et al., , ).…”

“…). Moreover, synchronization in migratory timing between bats and volant insects can promote en route pest suppression by these comigrating populations (Krauel & McCracken, ; Krauel et al., ; McCracken et al., ). In this light, the bats of Bracken Cave may serve the role of sentinels, regulating the passage of insects through the region, and reducing the impact of future generations downwind (Federico et al.…”

“…In this light, the bats of Bracken Cave may serve the role of sentinels, regulating the passage of insects through the region, and reducing the impact of future generations downwind (Federico et al. ; Krauel et al., ).…”

The grand challenges of migration ecology that radar aeroecology can help answer

“…For instance, bats pollinate fruit plants or consume insect pests; birds disperse plant seeds and invertebrates; and insects consume crops, transport crop and livestock diseases, and pollinate crops. In some cases, migrants may represent several effects, for example migratory noctuid moths are serious agricultural pests but also an important food resource for migratory bats in Texas (Krauel et al 2015, Frick et al 2017a).…”