Brazilian free-tailed bats (Tadarida brasiliensis) adjust foraging behaviour in response to migratory moths

Authors: KRAUL, JENNIFER - University Of Tennessee; RATCLIFFE, JOHN - University Of Toronto; Westbrook, John; MCCRACKEN, GARY - University Of Tennessee

Submitted to: Canadian Journal of Zoology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2017
Publication Date: 1/11/2018
Citation: Kraul, J.J., Ratcliffe, J., Westbrook, J.K., McCracken, G.F. 2018. Brazilian free-tailed bats (Tadarida brasiliensis) adjust foraging behaviour in response to migratory moths. Canadian Journal of Zoology. 96:513-520. https://doi:10.1139/cjz-2017-0284.
DOI: https://doi.org/10.1139/cjz-2017-0284

Interpretive Summary: Many species of crop pest insects migrate nocturnally within favorable winds at high altitude to rapidly access food resources over wide areas. Information about high-altitude insect migration is challenging to obtain, yet may be revealed by proxy through observations of larger predators. High concentrations of migrating insects are attractive as prey for insect-feeding bats, but migration events have not been linked to shifts in foraging behavior of bats. We recorded ultrasonic search and feeding calls of Brazilian free-tailed bats near ground level and at altitudes of 100 and 200 m above ground level in autumn. We found proportionally more bat activity at higher altitudes than near ground level during moth migrations. Bats decreased call frequency and bandwidth and increased call duration with increasing altitude and moth abundance. Knowledge of the timing, pathways, and intensity of insect migrations will lead to enhanced crop protection within and between production regions.

Technical Abstract: Insect migrations represent large movements of resources across a landscape, and are likely to attract predators capable of detecting and catching them. Brazilian free-tailed bats (Tadarida brasiliensis) track resources in time and space and consume large numbers of migratory noctuid moths. During migration, moths fly at high altitudes in layers that exploit temperature, wind speed, and wind direction, resulting in prey concentrations that should be attractive to bats. While bats are known to feed on migratory moths, migration events have not been linked to shifts in foraging behavior of bats. We predicted that bats alter foraging patterns by flying at higher altitudes when moths are migrating, and that they adjust their echolocation calls with altitude and numbers of moths. We recorded 1,104 Brazilian free-tailed bat passes at ground level and aloft at altitudes of ca 100 and 200 m above ground level on 13 nights in autumn 2012. We found proportionally more bat activity at higher elevations than ground level when migratory moth abundance was higher. Altitude and moth abundance explained 14-20% of variation in echolocation call parameters. Bats decreased call frequency and bandwidth and increased call duration both with increasing altitude and increasing moth abundance. Results support predictions that bats change foraging behavior in response to seasonal availability of migrating insect prey.