1 2 3 4 5 6 7 8 9 10 11 FM is a pulse that sweeps through a range of frequencies. These pulses are less suitable for long-range detection than CF pulses but can give other types of information such as distance to the target and texture discrimination. The number of pulses a second emitted by a bat is related to: • the wing-beat frequency; • the environment in which the bat is found; • the bat’s behaviour at the time, e.g. searching for or approaching insects. The pulse repetition rate of any species is not fixed. It is slowest and most characteristic in open environments but increases in cluttered situations when more information needs to be processed.This reaches a peak rate as a bat attempts to capture a prey item, when frequent updating of the distance to the target is required.The term feeding buzz aptly describes a very fast pulse repetition rate. Source: Extract from The Bat Detector Manual (Catto, Bats emit rapid, ultrasonic pulses and, by processing the information contained in the returned signals (echoes, are able both to orientate themselves and to detect prey in their environment. Bats have to use ultrasound because the wavelengths of lower frequencies are longer than most insects. However, the disadvantage of using high frequencies is that they are strongly attenuated in air, which limits the distance they can travel.The varied ultrasonic repertoires of bats are related both to the species of bat and type of environment in which they are flying. There are two broad types of ultrasonic signals constant frequency (CF) and frequency modulated (FM. Echolocation pulses are generally composed of various combinations of the two. CF is a sound produced atone frequency.There are two distinct types of CF calls, of short and long duration, which are used indifferent situations and by different families of bats.