Masters Theses

Date of Award

8-1987

Degree Type

Thesis

Degree Name

Master of Science

Major

Life Sciences

Major Professor

Gordon M. Burghardt

Committee Members

A. Echternacht, G. Rodda, R. Saudargas

Abstract

The feeding behavior of four species of garter snakes (Thamnophis butleri, T. melanogaster, T. radix, and T. sirtalis) was observed in an attempt to determine differences across species and between age groups with respect to capturing, handling and swallowing fish. The four species were chosen based on their similarities as well as their differences in habitat and prey preferences (T. butleri being known as an earthworm specialist, T. melanogaster as a fish specialist, and the other two species as generalists).

Wild-caught adult females, lab-reared yearlings, and newborn snakes were used for this study (total: 220 animals). In order to make comparisons possible, only fish prey, readily accepted in captivity by the four species, were used. Each snake was tested with two prey sizes: a fish that had a body width equal to the snake's head width (called a "small" fish) and another that was approximately larger than the snake's head width (called a "large" fish). The region by which the fish was captured (head, middle or tail) and the region from where ingestion was initiated (head or tail) were recorded. Two durations were also considered: handling latency (time it took a snake to handle a fish from capture to onset of ingestion) and swallowing latency (time it took a snake to ingest its prey).

Overall, feeding patterns were quite similar across species following a general sequence of capturing fish, maneuvering the jaws to either the head or tail of the fish (the head being "chosen" more often), and swallowing it. Head first ingestion was related to prey size: the larger the fish the greater the probability the snake would ingest it head first.

When this behavior was analysed more closely, species and age differences emerged. A major difference existed between adults and juveniles of the four species, although this difference was not as marked in the two specialist species as in the two generalists. Adults were more efficient at capturing and ingesting fish head first and took less time to handle and swallow their prey than did Juveniles.

Across species, T. melanogaster stood out as different from the other three species, whereas T. butleri and T. radix proved to be the most similar.

Considering differences within species and age classes with respect to their handling behavior of either a large or a small fish, T. melanogaster handled both sizes of prey in a time period that was not significantly different, T. butleri took significantly more time to handle a large fish whereas T. radix and T. sirtalis took considerably more time to handle a large fish as newborns but not as adults. These results support field observations that T. melanogaster is a fish specialist, T. butleri, an earthworm specialist, and the other two species, generalists.

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