The effects of perch height, time in residence and distance from opponent on aggressive display in male lizards

In antagonistic encounters individuals' displays reflect both the quality of the resource under dispute and their perception of the threat posed by their rival. All else being equal, as the value or threat to contested resources increases, so should an individual's level of aggression. Using a territorial species of Australian agamid lizard, the tawny dragon (Ctenophorus decresii), we tested three hypotheses about the relationship between territory quality and aggression. In three experiments we measured aggression whilst manipulating time in residence, perch height as a measure of territory quality and distance to an opponent's territory. Our measurement of aggression was a summary of behaviours used by tawny dragons in antagonistic displays (wrestling, hind-leg push-up display, chasing, raising of nuchal or vertebral crests, back arching, lateral compression, lowering dewlap, jerky walk and tail flick). Animals had significantly lower aggression scores when the opponent's territory was further away, but time in residence and perch height did not affect our measures of aggression. These experimental results provide good grounding for further tests of these hypotheses in field scenarios specifically manipulating distance between neighbours to determine what maintains the spatial distribution of tawny dragons in the wild.