When an animal attracts a mate or declares its ownership of a territory, it has to advertise. Signals used in communication usually have clearly defined functions, and signalling behaviour is sometimes associated with clear specialisations within the nervous system. Not only does the animal that sends signals need to make the meaning of its signals clear, but also the animals for which the signals are intended need to be able to capture, interpret and respond appropriately to those signals. So, during evolution, the motor signals that individuals of a species use to create signals need to be matched by appropriate sensory filters to recognise the same signals. For these and other reasons, communication is a fruitful area for investigation by neuroethologists.

In this chapter, we shall describe three different groups of animals that specialise in making and receiving particular types of signal. Two of these, crickets and song birds, use songs – extended patterned sounds – for communication. The other group are electric fish, which broadcast waves or pulses of electrical voltage in the water rather than audible sounds. The function of these electrical signals is not only to communicate with each other, but also to investigate their nearby surroundings. Sound and electric signals share the advantage that they can be used in conditions when sight is of limited use, such as at night or in undergrowth.