Many animals actively hunt their food on a daily basis, and insect-eating bats are no exception. However, these predators hunt in the dark hours of the night. While in flight, bats and insects alike employ complex manoeuvres to navigate their surroundings. Yet, insects need to evade being eaten and bats need to successively feed. To gain the upper hand, bats need to find, chase and capture their prey. Alberto Bortoni and colleagues from Brown University, USA, along with researchers from Lawrence Technological University, USA, and the University of Colorado, USA, set out to analyse the flight manoeuvres that Townsend's big-eared bats (Corynorhinus townsendii) use to successfully catch their meals. The stealthy Townsend's big-eared bat hunts at low speeds and, uniquely, performs aerobatic aerial manoeuvres while on the wing.
To analyse the flight behaviour of the bats, the team of researchers used mist nets to capture Townsend's big-eared bats at the American Museum of Natural History's Southwestern Research Station (SWRS) in Portal, AZ, USA. The researchers simultaneously collected moths and other insects with ultraviolet light live traps. The team released individual bats into an outdoor flight enclosure (6×4×2.3 m high cage), along with approximately one to five insects for them to catch. As each bat hunted its prey, their flights were video recorded, and the researchers recorded the bats’ quiet echolocation calls while they were hunting. The team then used mathematical modelling and simulations to analyse the bats’ flight behaviour from the videos. By doing this, the researchers were able to divide the hunting flights into distinct phases: the onset of pursuit; phase 1 – assessment; phase 2 – repositioning; and, if necessary, phase 3 – the chase.
At the start of pursuit, bats would initially detect their prey using their echolocation and slow down their flight speed. Then, during phase 1, the bats flight would pick up speed and the path was mostly straight, forward flight. Following this, the bats would enter phase 2, the repositioning phase, where bats completed an in-flight circular manoeuvre, bringing their body behind the flying insect. The researchers concluded that the first phases of the bats’ flight path allowed this species to perform in-flight manoeuvres at low flying speeds, and importantly, respond to any changes in prey movements, all while maintaining their pursuit.
Catching insects quickly is important as it saves the bats energy. Approximately one-quarter of the successful hunts (12 cases out of 44) needed to proceed to a third phase: the chase. During this phase, a prolonged active chase occurred, which usually resulted from the prey increasing their own flight speed during the bats’ repositioning phase. To eat the insect, bats would first catch the insect with their wings, but then move the insect to their membrane of skin between their legs and tail, which they use to flick the insect into their mouth all while remaining airborne.
Bortoni and colleagues discovered that all flight phases are incredibly important for the success of these bats in capturing their prey. Together, the stealthy flight, quiet echolocation calls and in-flight manoeuvres give the Townsend's big-eared bat the title of having the highest capture success rate out of any insect-eating bat species that hunts mid-air. These flying mammals really are acro-bats.
