The relationship between sensory specializations and behavioral specializations in two ecologically distinct species of squirrels was examined. It was predicted that the relative density of receptors in the glabrous forepaw skin of tree squirrels (Sciurus niger), which are skilled climbers and manipulate food items extensively, would be higher than that in ground squirrels (Spermophilus tridecemlineatus), which dig underground burrows. In addition to testing this prediction, several other aspects of the distribution of receptors were quantitatively examined in silver-stained material. As predicted, the relative density of receptors in the glabrous forepaw skin of tree squirrels is significantly higher than that in ground squirrels. Receptors are randomly dispersed and different classes of receptors (corpuscular vs. non-corpuscular) are intermingled in the palmar skin of both species. The proportions of the different classes of receptors do not differ among species.

No abstract

No abstract

Agonistic behavior of Gila Woodpeckers, including vocalizations, visual displays, and other related behaviors, is described. Interactions with both con- and heterospecifics were analyzed by stochastic processes, and it is shown that the timing of aggression toward a species coincided with the time during which that species was searching for nest sites or cavities. The behavior shown toward Flickers and Starlings appears to fulfill criteria for interspecific territoriality, and evidence is presented to support the contention that the function of this behavior is protection of nest sites and nest holes from competitors. The effects of intra- and interspecific territoriality on the distribution of the species involved were found to be significantly different. Simultaneous protection of different sized territories is discussed.

In a complementary neuroanatomical study by Brenowitz in 1980, it was shown that tree squirrels (Sciurus niger) have a higher relative density of mechanoreceptors in their glabrous forepaw skin than do ground squirrels (Spermophilus tridecemlineatus).The main purpose of this study was to test the prediction that tree squirrels would depend upon somatic sensory (cutaneous) input from their forepaws to a greater extent than would ground squirrels in food handling behavior. In addition, a series of more general questions about the sensory control of food handling was examined. First, using different sized food items, it was shown that food handling (rate of manipulation) is subject to sensory control, in general. Secondly, comparison of sham-operated groups with groups receiving median nerve (innervating the palmar surface) lesions showed that cutaneous input from the volar surface of the forepaw contributes to the sensory control in both species of squirrels. Thirdly, comparison of lesion effects in the two species showed that, as predicted, tree squirrels depend upon cutaneous input from their volar forepaw to a greater extent than do ground squirrels. Fourthly, by reanalyzing the above data it was shown that there is continued sensory feedback from food items rather than only an initial evaluation of them.