Previous articles have described how ultrasound is used by the animal kingdom. Bats are an example of one type of animal that uses ultrasonic waves as an aid whilst hunting for food, and will be used as the basis for this article. There are many different kinds of bats, but the information contained here is based on studies carried out on Myotis capaccinii, from a research paper by Aizpurua O et al., ‘Fine-tuned echolocation and capture-flight of Myotis capaccinii when facing different-sized insect and fish prey’, 2014, The Journal of Experimental Biology 217 pp3318-3325, published by The Company of Biologists Ltd.

The food source of M.capaccinii was revealed to be both insects and fish, which require different methods of hunting. As a consequence, the use of ultrasound by the bat must be altered accordingly. It should be noted that the appropriate term for the ultrasonic sounds bats use for hunting is ‘echolocation’, and can also be thought of as a type of animal ‘biological sonar’ (Wikipedia). The echolocation used by the bats during hunting was assessed, and some interesting findings were revealed. Firstly, one specific stage of hunting resulted in the bats emitting sounds that were broken up into two sections, termed ‘buzz I’ and ‘buzz II’. The results of the research showed that differences in the emission of both of these buzzes may play a key role in aiding in the differentiation between the hunting of insects and fish – a truncated buzz II (when compared to buzz I) was seen more frequently in cases where bats were hunting fish relative to insects, with ratios of almost 2:1 observed when bats were fishing. Furthermore, a longer buzz I involves both a ‘higher peak frequency’ and a ‘broader pulse bandwidth’ during emission, and this is thought to help the bat in identifying the position of the prey.

Secondly, whilst bats would touch water irrespective of whether they were hunting insects or fish, the way in which this occurred differed between the sources of prey. Although not directly related to ultrasound, this is still an important outcome of this research. If bats were hunting fish, their hind feet made water contact in a reckless and audible manner, with almost 70% inserting their feet more than halfway when compared to insect hunting. It is due to this hind foot insertion that it is postulated that the buzzes emitted from bats hunting fish (relative to insects) are therefore done so further away from the food source. In addition, bats were unable to make any more ultrasonic sounds when their feet were in contact with water, thus meaning all hunting-related decisions must be made prior to any movements made.

As is commonly the case when research is carried out, a number of further questions are generated from the results yielded. In this case one such question could centre on whether or not the changes in the echolocation discussed here are a natural phenomenon, or alternatively, a type of learned-behaviour. Future research should be able to deduce the answer to this question. If you have any ultrasound-related queries please do not hesitate to contact us.