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[Vol. 92 
males had been patrolling the ridge but stopped in order to perch in 
and defend the experimental landmarks. 
The Effect of Size and Contrast on Perch Attractiveness 
The larger of two mesh targets was approached significantly more 
often than the smaller one (W = 270.0, p < 0.005, Wilcoxon two- 
sample test; Table 2). The same was true for the darker of two 
targets when the choice was purely between a dark and a pale perch 
target (W = 298.0, p < 0.0001; Table 3). However, there were no 
significant differences with respect to perching times because flat 
vertical perches, whether constructed of cardboard or of plastic 
mesh proved ineffective in inducing male wasps to land. This was 
probably not due to an aversion to plastic mesh per se because a 
perch target constructed of five pieces of plastic mesh cut, curled 
into cones, and mounted on a pole top in such a way as to resemble 
the artificial ferns attracted 11 perching males in 16 trials. These 
flexible cones of plastic moved in the wind, as did the plastic ferns, 
perhaps providing a more attractive visual stimulus than the immo- 
bile flat mesh targets. 
Discussion 
The results of the experiments show that males of H. ustulata are 
clearly attracted to objects that are tall and large, and that stand out 
against the sky. Their readiness to investigate tall, large, and dark 
artificial landmarks, which do not resemble any natural perch sub- 
strates, demonstrates that certain visual properties are inherently 
attractive to the wasps. Indeed a substantial number of males aban- 
doned their perch trees and shrubs in order to take up residence on 
the aluminum and plastic landmarks, provided only that the artifi- 
Table 2. The effect of size of artificial perches on the frequency with which male 
tarantula hawks approached and perched on them during 15-min trials. 
Perch 
Material 
Target 
Size 
Number 
of Paired 
Trials 
Mean 
Approaches 
Mean 
Perching Time (min) 
Number 
of Males 
Perching 
Plastic 
Large 
14 
16.2 ± 6.5 
0.62 ± 1.4 
4 
Mesh 
Small 
8.1 ±4.5 
0.05 ±0.2 
3 
