Central place territorial defence in a burrow dwelling skink: aggressive responses to conspecific models in pygmy bluetongue lizards

In central-place territorial systems, individuals usually defend a central home site or refuge from conspecifics. Visual communication among individuals is crucial for social organization, provides information on current circumstances and allows assessment of conspecific intruders from a safe distance. We examined the role of visual cues in eliciting territorial defence behaviour in the endangered Australian pygmy bluetongue lizard Tiliqua adelaidensis. In field conditions, lizards discriminated between models of a conspecific and a similar-sized non-conspecific lizard. They displayed the highest level of aggression towards the conspecific model placed 5 cm from their burrow entrance. Male and female lizards displayed the same level of aggression and maintained an equivalent level of aggression throughout their activity season. Lizards showed less aggression towards models moved a further 10 cm from the burrow entrance. These results indicate that pygmy bluetongue lizards use visual cues in their social interactions and appear to display a central-place territorial defence social system. We interpret the distance effect as a reluctance to leave their burrow unattended because takeovers are easier if the resident is away from the burrow.