Like in other animal groups, species identification in bats is not always easy. Carolus Linnaeus recognized only two species of bat in Europe in 1758, the long-eared bat Vespertilio auritus, and the short-eared bat Vespertilio murinus. Two centuries later, about 30 bat species were known to live in Europe. However, modern taxonomy based on DNA analysis has revealed even more bat species, and new species are still being described ...
All those „relatively new species“ belong to sibling species' groups. The separation of those species has not been very sensible until recently, when sophisticated research methods became available for scientists. Therefore it is not surprising that bats belonging to the group of sibling species cannot be identified on species level easily. Often a set of relative characters, instead of absolute ones (which simply do not exist), have to be used to identify those species for sure.
Recently, a new handbook of European mammals was published in English (Dietz, Nill & Helversen, 2009), which summarizes modern achievements in the taxonomy and diagnostics of European bats. Identification characters presented in this book can be used to identify almost every European bat.
Today, bat species are very often identified on the basis of their sound. Since Ingemar Ahlén's work on the sound diagnostics of European bats (Ahlén, 1981) many bat scientists as well as amateurs in Europe have used sound characters to identify bats in flight. During a few decades the sounds of European bats have become the main source of information in various types of field research including bat survey, monitoring bat populations, measuring bat flight activity, revealing the value of different habitats for bats, etc.
The identification of bats based on their sound
Ultrasound equipment called „bat-detector“ is used to find, identify and count bats in flight. Several types of detectors exist, two of which have been widely used in northern Europe.
First, heterodyne detector (like Pettersson D100 and Pettersson D200). This is a pocket-size apparatus which has a sensitive ultrasound microphone and a heterodyne system which makes bat sounds audible to humans. Using different characters of sound many bat species (especially those belonging to the group of narrowband bats; Masing, 2006) can be identified on spot, just by listening to the detector.
Second, time-expansion detector (like Pettersson D240x and others). Those can be also pocket-size, and usually include also a heterodyne system. In this type of detector the original bat sound is expanded (often 10 times), thus species specific character states can be picked by a human ear. This type of detector helps to identify also broadband bats. Those emit often very short pulses not identifiable from a heterodyne detector.
Both types of detector are widely used in bat surveys and bat monitoring; and this is also the very equipment that our research team has used during bat work in European towns.
Fig. 1. Pettersson D200 (heterodyne, on the left) and Pettersson D240x (heterodyne and time-expansion, on the right) bat-detectors.
Fig. 3. Kazimieras Baranauskas doing fieldwork on bats in Vilnius. A Pettersson D200 detector and a strong hand torch can help to identify most bat species present even during the darkest night. (photo by Matti Masing, 2010)
Ahlén, I. 1981. Field identification of bats and survey methods based on sounds. – Myotis, 18—19, 128—136.
Dietz, C., Nill, D. & Helversen, O.v. 2009. Handbook of the Bats of Europe and Northwest Africa. A & C Black Publishers Ltd, 400 pp.
Masing, M. 2006. Nahkhiirte vaatlused rannikul seoses tuuleturbiinidega. [Observations of bats on the coast in connection with wind turbines] Rmt: Taastuvate energiaallikate uurimine ja kasutamine. (Toim. V. Tiit) Seitsmenda konverentsi kogumik. Tartu, Estonia: 95-111.