Factors influencing aggressive behavior in the dragonfly, Pachydiplax longipennis.

Males of many dragonfly species defend territories along the margin of lakes, ponds, and streams. In a series of experiments, we tested whether the maturity or perch-height of combatants affected aggressive behavior. We placed dead decoys of different age on perches of different heights, and counted whether attacks were made by resident territorial males perching at different heights. Older males were more likely to attack decoys than younger males, but the age of the decoy had no effect on whether it was attacked. Decoys on short perches were attacked more often than those on tall perches, and territorial males on tall perches were marginally more likely to attack decoys than territorial males using short perches. In conclusion, it appears that males on tall perches are either perceived as more threatening/dominant than those on short perches, or that short perches are more desirable for this species