disk-winged bat: Communicating within a leaf Unlike most bats, which hang upside down in their roosts, the Spix’s disk-winged bat of Costa Rica clings head up inside rolled up leaves. A recent study suggests these leaves affect the social calls of the bat. image To cling onto the inner surface of rolled up leaves of e.g. the lobster-claws plant, Spix’s disk winged bats (Thyroptera tricolor) have specialised discs on their thumbs and hind feet, which act as suction pads. The bats use the furled up leaves to escape from predators and extreme weather conditions. Spix’s disk-winged bats are also social, tending to form groups of five or six bats which stay together for many years. It is important, therefore, that these bats are able to recognise the calls of one another. This is especially so as their roosts only last a day or two before they unfurl. The bats are thus not just able to learn and remember the whereabouts of their roost, as they may be foraging when the group moves. Gloriana Chaverri and Erin Gillam observed that the calls of bats flying outside of the roost were not recognised by fellow group members inside the roosts. “We started to wonder if the leaf was somehow affecting call fidelity” said Chaverri. To explore this idea, speakers were placed at different positions within the leaf, either at the narrow bottom or the wide opening, with microphones placed opposite to the speakers. Recorded bat calls were subsequently played through the speakers to see if the microphones could pick up an effect. The research team found that incoming calls from bats outside the leaf were significantly amplified, by as much as 10 decibels. This equated to a bat being heard from 33 feet further away. However, they also found that the calls were distorted, with the frequency of some calls being being muted, perhaps explaining why bats outside the roost were not being recognised. Instead bats within the leaf were responding indiscriminately to calls from bats within and outside their group. These “response” calls, though also distorted, were typically identified by their fellow group members. Response calls consist of up to 25 sounds and are sufficiently more complex than regular calls. It is conceivable that it is this complexity which allows the bats to recognize the calls of their roost members in spite of the degraded signal. It therefore seems that the Spix’s disk-winged bat has been able to overcome the trials and tribulations of communicating within a leaf. By Matthew Everatt
Posted on: Thu, 17 Oct 2013 23:40:36 +0000