An illegitimate receiver is an organism that intercepts another organism's signal, despite not being the signaler's intended target. In animal communication, a signal is any transfer of information from one organism to another, including visual, olfactory (e.g. pheromones), and auditory signals. If the illegitimate receiver's interception of the signal is a means of finding prey, the interception is typically a fitness detriment (meaning that it reduces survival or reproductive ability) to either the signaler or the organism meant to legitimately receive the signal, but it is a fitness advantage to the illegitimate receiver because it provides energy in the form of food. Illegitimate receivers can have important effects on the evolution of communication behaviors.