Doctoral Dissertations

Date of Award

12-1974

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Psychology

Major Professor

Gordon M. Burghardt

Committee Members

Steven Handel, Joseph Howell, William Calhoun

Abstract

Descriptions of social organization patterns between and within various species are required to answer evolutionary questions about social behavior. Social organization is often expressed in patterns of spatial distribution such as habitat preferences, activity cycles, and habitat utilization. These distribution patterns were investigated in the common snapping turtle, Chelydra s. serpentina, in the laboratory and in the field. The first experiments evaluated juvenile substrate preferences in two-choice tests. The substrates used were equal areas of sand and pea gravel. Turtle positions on either substrate were recorded at various temperatures. A slight preference for sand could not be replicated, and temperature had no apparent effect on substrate choice. Young turtles in the field were found on various substrates. While soft sand may be preferred, young turtles adapt to a range of suitable substrates. Juvenile turtles in a 1 m diameter pool, clustered around rocks. Therefore, preferences for open versus obstructed areas were tested with five hatchling and nine juvenile turtles. One-half of the pool contained rock obstructions, and the other half was open. Photographic records indicated that both groups preferred the obstructed area at night. During daylight the larger turtles did not prefer either half of the pool. However, the hatchlings still preferred the obstructed half. In the field, turtles were found around obstructing or camouflaging objects. Possible functions of these preferences could have been increased protection and food availability. Diurnal cycles were measured during area preference tests. Both groups of young turtles showed significantly different heightened daytime activity and lowered nightime activity. Adult turtles in a 0.8 ha pond were tracked by radio telemetry in fall and spring. Nighttime activity was significantly greater than for other time blocks. However, some turtles were active at all hours of the day. The differences between laboratory and field diurnal cycles may have been due to specific habitat conditions in the laboratory, developmental differences between the groups of turtles, or artifacts of captivity. The extent of confounding due to captivity requires further evaluation. Fall and spring activity rates for the field turtles were not directly comparable due to differences in location techniques. Activity rates were quite variable between turtles. Spring activity rates were negatively correlated with turtle size. Activity rates showed little correlation with ambient temperature, probably because an attenuated range of temperatures was sampled. Cycles of activity and inactivity were different in two size classes of turtles. Large adults had long inactive periods interrupted by short range movement. Smaller adults had short durations of inactivity and frequent periods of long range movement. The turtles in the pond extensively used one or more home sites. These sites resembled the "forms" described for box turtles. Turtles spent inactive periods at home sites, and repeatedly returned to these following activity. Home sites were heavily concentrated in obstructed areas. Adult turtles had home ranges which included an average of 38% of the pond area. This estimate was probably low because of the limited time during which movements were sampled. Home range estimates were considerably variable between turtles. The extensive habitat utilization supports earlier reports that home ranges for aquatic reptiles are highly habitat determined. While the home range sizes and overlap suggested considerable conspecific tolerance, the specificity of home sites and withdrawal responses of a juvenile when an adult approached provided indirect evidence for competition between conspecifics. The results suggested organizational patterns and conspecific responses permitting adaptive differential utilization of space within a microhabitat. Only lack of description on hard-to-observe species support biases against social complexity in reptiles. The flexibility of organizational and behavioral patterns in a range of habitats should be further investigated.

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