Fighting behavior and prior residency advantage in the territorial dragonfly, Perithemis tenera

Abstract

Many factors, including residency status, body size, age, and energetic reserves, have been implicated as possibly determining the winner in animal contests. In this study I investigated which of these factors were correlated with the outcomes of naturally-occurring territorial contests between male amberwing dragonflies (Perithemis tenera). Amberwing contests consist of non-contact interactions and are characterized by a series of distinct stages that represent different levels of escalation. Prior residents did tend to win, but interestingly this residency advantage only occurred in interactions that were not escalated. For both non-escalated and escalated interactions, body size (wing length) did not influence the outcome. Age was correlated with outcome for escalated interactions, with the younger of the pair tending to win. Winning males had also spent less time in male-male interactions both the day of the interaction and during their entire life, suggesting that energy reserves may also affect the outcome of contests. In contrast to escalated interactions, age and time spent in male-male interactions was not related to the outcome of non-escalated interactions. The difference between the two opponents' sizes, ages, and time spent in previous male-male interactions did not correlate with duration or escalation level of contests. These results suggest that non-escalated interactions may occur when intruders are simply assessing the quality of the site. Contests that do not escalate, and thus the prior residency advantage, are probably a result of the intruder not challenging for ownership because the value of the territory is too low.