Archive for 03/11/2010

What is it like to be a bat?

The question often quoted is “what is it like to be a bat?” but this question will eventually be answered in a scientific way, by artists too, but probably will still worry some philosophers. A recent paper by Greif and Siemers makes a start at a scientific understanding.

Here is the abstract:

In the course of their lives, most animals must find different specific habitat and microhabitat types for survival and reproduction. Yet, in vertebrates, little is known about the sensory cues that mediate habitat recognition. In free flying bats the echolocation of insect-sized point targets is well understood, whereas how they recognize and classify spatially extended echo targets is currently unknown. In this study, we show how echolocating bats recognize ponds or other water bodies that are crucial for foraging, drinking and orientation. With wild bats of 15 different species (seven genera from three phylogenetically distant, large bat families), we found that bats perceived any extended, echo-acoustically smooth surface to be water, even in the presence of conflicting information from other sensory modalities. In addition, naive juvenile bats that had never before encountered a water body showed spontaneous drinking responses from smooth plates. This provides the first evidence for innate recognition of a habitat cue in a mammal.

Animals must have senses and behaviours that fit their environment; they must recognize elements of the environment and use the appropriate behaviours for that type of place. What part of this fit is innate and what part is learned, or even what senses/behaviours are used, is not known of most animals. Bats relationship to water is a useful subject to explore these questions.

For bats water can be a source of abundant insects that are easily tracked against the water. Bats also drink on the wing. And finally they can get ‘ground effect’ help by flying close to the surface of water. So water is important for bats to recognize and to echo location, water is unique in the natural environment.

When a bat flies over a water surface and the axis of its echolocation beam intersects with the surface at an acute angle, the main energy of the echolocation calls is reflected away from rather than back towards the bat, so it does not receive an echo from ahead. However, some off-axis energy of the sound beam hits the surface perpendicularly and does generate an echo returning from straight below the bat.

In a flight room, bats were tested with plates of metal, plastic and wood which were smooth or textured. The smooth plates were like water to echo-location but not to sight, taste, smell or touch. The behaviour measure used was drinking attempts. The fifteen very different species tested tried to drink from smooth plates but not textured ones. In some situations there was ample information from other senses to indicate that the surface was not water but this was overruled by the echo-location information. Juveniles that had not encountered water in nature also attempted to drink, indicating that the recognition is probably largely innate. Many bats made repeated attempts and in those cases the behaviour may be somewhat automatic or hardwired.

With respect to small-scale navigation and habitat recognition, bats thus appear to be an extreme example of predominant reliance on one main sensory modality.

So there it is - one little interesting step towards knowing what it feels like to be a bat.
Greif, S., & Siemers, B. (2010). Innate recognition of water bodies in echolocating bats Nature Communications, 1 (8) DOI: 10.1038/ncomms1110