18 
Psyche 
[Vol. 87 
These birds selected the spider on the incomplete web 12/13 times. 
The results of the second choice are also clearly non-random and 
demonstrate that the stabilimentum had a negative influence. The 
results show that both the web and the stabilimentum inhibited 
predation by the blue jays. 
Comparison of the results obtained during the initial exposure of 
each bird with the results from subsequent trials indicates that this 
avoidance of webs and stabilimenta is a learned response. Initially the 
birds did not discriminate between the three choices, but they did so 
after experiencing web contact. 
After having contacted the webs the blue jays exhibited behaviors 
such as head shaking, wiping the beak, and preening. The birds 
displayed these cleaning behaviors for periods ranging from 30 
seconds up to an hour after web contact. The web adhered to the 
feathers and caused some clumping, mainly of the head and breast 
areas. Cleaning activities were apparently directed at removal of the 
portions of the web which had adhered to the birds. 
It is possible that the web contains a substance which is noxious or 
toxic to birds when ingested. However, during the experiments, I 
observed some of the birds eating the webs after coming in contact 
with them. The fact that the birds ate the portion of the webs which 
adhered to their feathers suggests that the web did not contain 
noxious or toxic substances. 
Based on the behaviors exhibited by the blue jays, I suggest that the 
noxious quality of the web is due to the physical adherence of the web 
to the bird’s feathers, and the resulting clumping of the feathers. 
Apparently stabilimenta are constructed only by diurnally active 
orb-weavers. A second generalization is that many of the diurnal orb- 
weavers are conspicuously colored (Levi, 1968). Since it appears that 
the web is a noxious stimulus to birds, then it is reasonable to suggest 
that both the conspicuous coloration of the spider and the presence of 
stabilimenta make the web more obvious, thus facilitating avoidance 
by predators. The stabilimentum would then be analogous to 
aposematic (warning) coloration in insects. The stabilimentum and 
bright coloration would have an effect on visually orienting preda¬ 
tors, such as birds, and would be effective during daylight hours when 
such predators are active. This hypothesis of advertisement was 
originally discussed by Robinson and Robinson (1970), though they 
had no evidence of a noxious element. 
