Foraging tactics of a terrestrial salamander: Costs of territorial defence

Red-backed salamanders, Plethodon cinereus, established territories in laboratory chambers. Their foraging tactics, on two types of prey differing in caloric profitability and defence behaviour, were observed under a series of experimental conditions in which competitive threat was increased: no competitor present < familiar conspecific's pheromones present < unfamiliar conspecific's pheromones present < familiar conspecific intruder present < unfamiliar conspecific intruder present. As the degree of competitive threat increased, more time was devoted to territorial defence (displays and biting) at the expense of foraging. Simultaneously, the territorial residents gradually shifted from a specialized diet on the more profitable prey type to an indiscriminate diet, even though prey densities and the residents' encounter rates with each prey did not change. The presence of unfamiliar pheromones and both intruders led to approximately a 50% decrease in the residents' rates of net energy gain, about 80% of which was due to the time withdrawn from foraging and 20% due to change in diet. Changes in foraging time and diet both reflected the costs of territorial defence.