In underwater acoustics and fisheries acoustics the term is also used to mean the effect of plants and animals on sound propagated underwater, usually in reference to the use of sonar technology for biomass estimation
The most recent advances in bioacoustics concern the relationships among the animals and their environment and the impact of anthropogenic noise.
Listening is still one of the main methods used in bioacoustical research. Little is known about neuropyhsiological processes that play a role in production, detection and interpretation of sounds in animals, so animal behaviour and the signals themselves are used for gaining insight into these processes.
An experienced observer can use animal sounds to recognize a "singing" animal species, its location and condition in nature. Investigation of animal sounds also includes signal recording with electronic recording equipment. Due to the wide range of signal properties and media they propagate through, specialized equipment may be required instead of the usual microphones, such as hydrophone (underwater sounds), ultrasound detector (very high-frequency sounds), or laser vibrometer (substrate-borne vibrational signals). Computers are used for storing and analysis of recorded sounds. Specialized sound-editing software is used for describing and sorting signals according to their intensity, frequency, duration and other parameters.
Animal sound collections, managed by museums of natural history and other institutions, are an important tool for systematic investigation of signals.
But since the methods used for neurophysiological research are still fairly complex and understanding of relevant processes is incomplete, more trivial methods are also used. Especially useful is observation of behavioural responses to acoustic signals. One of such is phonotaxy - directional movement towards the signal source. By observing response to well defined signals in controlled environment, we can gain insight into signal function, sensitivity of the hearing apparatus, noise filtering capability, etc.
Sounds used by animals that fall within the scope of bioacoustics include a wide range of frequencies and media, and are often not sound in the strict sense of the word, i.e. compression waves that propagate through air and are detectable by the human ear. Katydid crickets, for example, communicate by sounds with frequencies higher than 100 kHz, far into the ultrasound range. Lower, but still in ultrasound, are sounds used by bats for echolocation. On the other side of the frequency spectrum are low frequency-vibrations, often not detected by hearing organs, but with other, less specialized sense organs. The examples include ground vibrations produced by elephants whose principal frequency component is around 15 Hz, and low- to medium-frequency substrate-borne vibrations used by most insect orders. Many animal sounds, however, do fall within the frequency range detectable by a human ear, between 50 and 15,000 Hz. Mechanisms for sound production and detection are just as diverse as the signals themselves.