92 
Psyche 
[March 
degrees. Immediately, one male returns directly to defend the terri- 
tory while the defeated male returns many seconds later to rest or 
does not return to the area at all. Unfortunately, the flight speed 
was so great, and the distance so far, that I was unable to determine 
which male claimed the territory, or whether either regularly did, 
but I would hypothesize that the lower and therefore faster male 
usually dominates. As Johnson (1962) stated, this is the final step 
in establishing territorial dominance between two males. At any 
time one male may abandon this territorial dispute and retreat out 
of the area leaving it for the remaining male. In further agreement 
with Johnson (1962), I observed that the original owner often 
retains the territory. Such disputes generally last from 5 to 50 
seconds and terminate with territorial possession and perch display 
by the dominant male. 
Perching Position 
The perching position of Pachydiplax longipennis is probably de- 
termined by several factors including wind, sun intensity, air temper- 
ature, the kind of perch, and the behavior of other dragonflies. 
Under typical summer daytime conditions when the wind speed is 
low, a male in an open situation exposed to full sunlight, usually 
aligns his body along the length of the perch. He raises his abdomen 
only a few degrees and brings his wings forward (Fig. ib). Every 
10 to 60 seconds he leaves his perch to patrol but returns directly if 
undisturbed by intruders. Very rarely did any male raise his abdo- 
men to the extent illustrated by Johnson (1962: Fig. 2). On 
windier days, males keep their wings fully outstretched and at right 
angles to the prevailing wind. Only on hot calm days, when the air 
temperature rose above 30 0| C, did perching males raise their abdo- 
mens higher. 
My observations, coupled with Johnson’s (1962), suggest that 
male perching behavior is influenced by at least four factors includ- 
ing thermoregulation, aerodynamics, predator avoidance, and terri- 
torial display. It is interesting to note that whereas Johnson (1962) 
and Williamson (1900) reported that males generally perch with 
their abdomens directed upwards, this behavior was rarely seen in 
Massachusetts populations. Johnson and Williamson’s observations 
were made on sunny days, at stations where daytime temperatures 
are typically 2-4°C higher than those prevailing in Massachusetts. 
This suggests that this behavior may be temperature dependent. As 
male-male territorial interactions were otherwise fully developed in 
the Massachusetts populations, I suspect that the abdomen orienting 
