The Natural History of the Alabama map turtle, Graptemys pulchra Baur, in Alabama

Abstract

From June 1969 until October 1972 the natural history of the Alabama map turtle, Graptemys pulchra, was studied in southern Alabama. Over 500 specimens were collected, of which 286 were measured, marked, and released, and 91 were autopsied for reproduction and food studies. Graptemys pulchra was the most abundant turtle in the study area and its primary food item, the imported oriental mussel Corbicula maniliensis, was the most abundant macro-invertebrate. Large, mature individuals of G. pulchra were more abundant than juveniles. Home range was apparently more stable in males, but only females exhibited homing behavior. I found that females either returned to the home area or remained at the displacement site. Those returning to their original localities moved distances of 24 river channel km (15 mi) or more up- and downstream. Growth is rapid in juveniles but declines sharply at maturity and approaches zero shortly after maturity. Males reach sexual maturity in their third or fourth year, but females apparently do not reach maturity until they are approximately 14 years old. Maximum size in females is reached in about 23 years, and natural longevity probably exceeds 50 years. Sexual dimorphism with respect to size is pronounced, the largest male studied being about half the carapace length of the smallest female (120 mm vs 212 mm). Although sperm were present in the male reproductive tract throughout the year, mating behavior was observed only in autumn months, suggesting that sperm is stored in females. The male courtship sequence is similar to that described for other aquatic emydines, except that the "titillation tool" of the male is the snout, rather than elongate fore-claws. Elongate fore-claws are not characteristic of adult males. Predation probably resulted in the destruction of 95 percent of the natural nests during the study period, although some reproductive seasons were much more successful than others. The major diurnal predator on nests was the fish crow, and the major nocturnal predator was the raccoon. The only significant ehemies of adults are man and possibly the alligator snapping turtle, Macroclemys temmincki. Reproductive potential vafied from 7 to 71, depending on the size of the female, and averaged 29 eggs per season per female. An average of 4 (1-6) clutches were laid per season per female. Extra-uterine migration of ova was usual. Nests were located 1-20 m from the water's edge, usually on large, exposed sandbars. Coarseness of the sand seemed to be the major criterion on which nest site selection was based. Incubation required from 74 to 79 days at 29°C, the average nest chamber temperature in natural nests. Infertility of individual eggs and entire clutches was common. Males and females under 100 mm carapace length were primarily insectivorous, whereas juvenile and adult females in the study area subsisted almost entirely on Corbicula. Feeding generally began in May and ended in October. Since growth ceased in early September, food assimilated during September and October was probably stored for winter. The most significant determinant of seasonal activity was water temperature. Activity and feeding decreased sharply at water temperatures below 19°C (66°F). Complete inactivity (hibernation) of the entire, population during the winter was not observed. No significant interspecific competition with other turtle species was found.