[ Tiffany Peacock. Image: Oliver Hammond ]

The gazelle's leaping behavior, the nestlings' begging, the expensive suit - all of these things are signals. All are intended to convey information about a signaller, to a signal receiver. For humans, the fancy suit - like a fast car, an expensive bottle of wine, or a precious gemstone - indicates some property or quality of the signaller. In this case, that property might be the relative wealth of an individual.

Gazelles may be doing something similar with their jumping or "stotting" displays. Biologists have argued that the stotting display serves as a signal of quality to potential predators. "I'm a strong and healthy gazelle," the display demonstantes. "See how high I can jump? It would be a waste of your time and energy to chase after me!" Baby birds, through their begging behavior, may be informing their parents about how badly they need to be fed. Additional examples are easy to find. Bull elk signal their quality to rivals and to potential mates with a large rack of antlers and a loud bugling call. A peacock's fine tail serves to advertise the high quality of its bearer to potential mates.

These signals share an additional feature: all are costly to produce and send. Expensive suits, fast cars, wine, or jewelery are not cheap in terms of that all-important human currency, money. Similarly, the stotting display is expensive - albeit in a different sort of currency - to the gazelle. By leaping up and down, a gazelle is expending the very energy that it will need desperately should a chase ensue. Squawking to one's parents takes energy and may also alert predators to the location of a nest; producing and bearing a huge flashy tail is also energetically expensive, not to mention risky when predators are around.

Why do so many different species of animals all use signals that are inherently expensive, in a wide range of different signalling contexts? Why not simply "whisper" the message to the intended receiver, rather than producing an elaborate and costly display? And why do these expensive signals seem to be so convincing to the intended signal receivers?

An area of game theory called signalling theory examines the nature of communication behavior, and attempts to answer these sorts of questions. This tutorial is intended to provide an introduction to this fascinating field, with a particular focus on its application in biology. Signalling theory can be applied broadly to human and non-human alike, and as such will be of interest to researchers in a wide range of fields, including biology, economics, sociology, anthropology, political science, communication studies, linguistics, philosophy, and psychology. For this reason, I have tried to keep the necessary background to a minimum, so that the text will be accessible to all interested readers, irrespective of any prior background in animal behavior or evolutionary biology.