The ethology and sociobiology of animal communication

Sign stimuli and releasers

• Comparative ethologists Heinroth, Huxley, Lorenz, Tinbergen: identified simple Fixed Action Patterns triggered off by Sign Stimuli
• In some (but not all) cases, the sign stimuli are features of another animal (usually a conspecific) that seems to have no other function, and therefore can be assumed to have evolved to act as a trigger; such stimuli are called Releasers
• Often there are also characteristic FAPs that make the releasing stimulus more visible or effective
• The comparative ethologists conceived of such releaser/fixed action patterns as a system of (partly instinctive) communication between the two animals (the sender and the receiver)

Communication or exploitation?

• Sociobiologists e.g. Krebs & Dawkins questioned the co-operative implications of terms like communication
• They stressed instead that if the releaser is to evolve, showing it must confer some advantage on the sender.  So instead of communication we might talk about advertisement or manipulation
• If the receiver's response is to evolve, it should also confer advantage on the receiver.  But there might be an advantage to responding to other stimuli like the signal in question, and the sender mimics such stimuli
• The evolution of such exploitative signals depends on receiver psychology - the set of stimuli the receiver will respond to
• Some signals clearly benefit both sender and receiver (but not necessarily equally)
• Signals that benefit the receiver but not the sender would be examples of altruistic behaviour so would require special conditions (kin selection, reciprocation) if they are to evolve

Communication and intention

• Some people argue that if we want to use the word "communication", the sender must intend to send a particular message to the receiver
• Neither ethology nor sociobiology requires this.  It is enough that the message produces a reliable effect on the receiver's behaviour
• The receiver need not be of the same species as the sender - e.g. in communication between predators and prey, or between different species attacked by the same predators
• Dawkins refers to the Extended phenotype: communication allows an animal's genotype to modify the bodies of other animals, not just its own