5.1 Field identification Bats are identified most easily in the hand, but practice allows identification by a variety of other means, such as bat detectors, droppings or flight pattern. Such methods have varying reliability and identifications may not be acceptable to recording authorities. A beginner will have to use an identification key (see Appendix 5) and, by looking at a number of characters, achieve a correct identification. It is essential, then, to be able to handle bats properly and confidently. Bats are very vulnerable to disturbance, particularly in their nursery colonies, where excessive disturbance can cause them to desert their young, or during hibernation, where arousal uses up energy reserves. They should, therefore, be disturbed as little as possible. Similarly, if they are being handled, they should be confined for as short a time as possible; but a bat in the hand offers additional data that can be recorded for various personal or wider studies, e.g. sex, biometrics, physiology and parasites. A museum specimen is no longer necessary to provide an acceptable record, and a preserved specimen often masks useful features. While a museum specimen is (or should be) available in perpetuity and will continue to provide research material, the live bat has many advantages. It allows both the opportunity to see pelage and skin in their natural colours and textures, and the monitoring of changes in certain physiological and morphological features. Complete familiarity with the topography of a bat is essential for successful identification and further studies. Features used in the identification and other aspects of the study of British bats are described on the generalised bats illustrated (Figure 5.1) and there area number of guides available that give further details (see Appendix 5). Callipers will be needed for any essential measurements. Almost all essential dental characteristics can be seen with ax hand lens – and a cooperative bat.