Skyrocketing Flights as a Previously Unrecognized Behaviour of Open-Space Foraging Bats

The airspace of the lower troposphere is an important habitat for many animals, including open-space foraging bats. Yet, we are missing a detailed understanding of how bats forage in the seemingly unstructured open space. As part of an exploratory study, we present data on flight activity for Taphozous theobaldi (Dobson 1872), an aerial insectivore known to hunt in the open space close to mountain ridges in central Thailand. Using logger data from five individuals, covering a total period of 26 observation days, we show that T. theobaldi remained airborne for 4.8 ± 3.1 h per night (mean ± SD). We confirmed that T. theobaldi performed altitudinal flights with quick ascents, short horizontal flights followed by descents. Each night, T. theobaldi engaged on average in 2.9 ± 1.4 altitudinal flights during which they reached an average peak altitude of 306 ± 53 m above cave elevation. On average, bats spent about 14% of the total foraging time in altitudinal flights. We conclude that T. theobaldi is a regular, but most likely not an obligatory exploiter of high altitudes. We speculate that T. theobaldi may ascend to higher altitudes in search for insects, for example migrating or dispersing insects at higher air layers or swarms of hill-topping insects. Short altitudinal flights with fast ascents and descents (a slender bell-shaped flight trajectory over several 100 m altitude) may present a so far unrecognized flight behaviour of bats that may be more widespread among other aerial insectivores.