Doctoral Dissertations

Date of Award

8-1991

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Life Sciences

Major Professor

Gordon M. Burghardt

Committee Members

Arthur Echternacht, Neil Greenberg, John Malone, Rich Saudargas

Abstract

Due to the longstanding and widespread beliefs regarding their lack of sociality, little is known about the aggregative behavior of snakes. A consideration of previous work not only indicates that snake aggregation is a social phenomenon but also suggests a variety of factors that may influence this behavior. A consideration of these factors (diet, familiarity, kinship) form the basis of this research. Fifty-nine T. s. sirtalis neonates from 2 litters of a Michigan population were measured for mass and snout-vent length, then tested prior to feeding for initial chemical prey preferences and site choice based on conspecific feces. Animals were then placed into group housing situations of 8 balanced for litter, sex, and initial chemical prey preferences, and fed either worms, Lumbricus terrestris (2 groups), or mosquito fish, Gambusia affinis (2 groups). Two groups consisted half of animals on each diet, and 2 additional groups consisted half of T. sirtalis on one diet and half of another species, T. butleri, on the same diet. The remaining animals were maintained in isolation. After a maintenance period, snakes were again measured, tested for chemical prey preferences, and tested for site choice based on both conspecific feces and prey surface cues. The remaining 38 animals not housed with T. butleri were then observed for aggregation behavior in a large arena with 8 identical shelters, after which all animals were again measured. The main differences in snout-vent length and mass occurred between animals in the different litters, with litter 16 animals being consistently larger than litter 10 snakes. The lack of difference in growth between animals on different diets is assumed to indicate a negligible difference between the health of the subjects. The T. sirtalis in this research prior to feeding experience showed responses to both fish and worm extract (that were significantly above responses toward a water control), with a preference for worm cues indicated by a greater frequency of predatory attack. Litters showed different initial preferences, litter 10 having a strong worm preference, whereas litter 16 showed no preferece. After experience with prey, shifts of preference were more frequently in favor of the familiar prey, although the strongest effect was again a litter difference. Litter 10 snakes showed no change from their initial preferences, still showing strong worm preferences only slightly decreased by a fish diet, whereas litter 16 animals fed fish acquired a moderate fish preference, while those feeding on worms still showed no preference. In an Initial Feces-Based Site Choice test, T. sirtalis were shown to have an overall bias in favor of conspecific feces carrying worm cues. In a Final Feces- Based Site Choice test, there was no significant preference for feces-marked sites, though in general animals chose the feces bearing familiar prey cues. There was a difference between the sexes such that males preferred worm cues whereas females preferred fish cues. Sites marked with worm prey surface chemicals were preferred by animals fed worms, snakes in litter 10, and males. Thamnophis sirtalis formed small, scattered aggregations under several identical shelters. Litter 16 snakes significantly associated with siblings, whereas litter 10 animals were less aggregatory and more active in the arena. Animals from 3 of 6 housing groups associated with familiar animals at a significant rate. There was some evidence that females were stronger aggregators, preferring the same sex, whereas males preferred aggregating with the opposite sex. There was little influence of diet in aggregation behavior, animals on both diets possibly being nearer animals fed worm. Comparisons were made between the results of different experiments within this research, suggesting that smaller animals preferred worm cues. There was also evidence that subjects preferred to be nearer animals fed the same prey that was their preference in Prey Surface-Chemical Site Choice. Results support the possibility of information extraction in this species, suggest kin recognition, and possibly individual recognition. Results of experiments with T. sirtalis are also compared with prior work using T. butleri, and further research is suggested to continue our understanding of aggregation in snakes and other animals.

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