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A substantial degree of broad and local scale geographic variation in life history traits (e.g., body size, age and size at maturity, egg size, clutch size and frequency) has been documented in the painted turtle (Chrysemys picta)(Iverson and Smith 1993; Lindeman 1996; Rowe 1994, 1997). Painted turtles are generally omnivorous (Ernst et al. 1994) and high degrees of carnivory may be positively related to growth rates, body size, and reproductive output among populations of painted turtles (Gibbons 1967; Gibbons and Tinkle 1969; Lindeman 1996; MacCulloch and Secoy 1983). Recently, Lindeman (1996) summarized the literature on painted turtle dietary habits and found extreme carnivorous or herbivorous populations throughout the range of the species. In order to attribute some of the variation in life history traits to variation in dietary habits of painted turtles, we clearly need more data on the diets of painted turtles throughout their distribution (Lindeman 1996).
We studied the dietary habits of adult midland painted turtles (Chrysemys pieta marginata) at Miller's Marsh on Beaver Island (W85 deg.30.89'; N45 deg.38.06') located in northern Lake Michigan, USA. Miller's Marsh was a small marsh system (max depth approx. 1.5 m and about 4-5 ha in surface area) with dominant submergent vegetation that included Nuphar variegatum, Potamogeton amplifolius, and P. natans. We collected painted turtles in baited fyke nets between 30 June and 5 July, 1994 and between 5 June and 2 August, 1995. Upon capture, carapace length was measured to the nearest 1 mm using calipers, body mass was measured to the nearest 10 g using a spring scale, and stomach contents were obtained by stomach flushing (Legler 1977). A weed spray can was used to deliver water through a rubber tube (0.5 cm diameter) that was inserted through the mouth and into the stomach. Turtles were held by hand and a rubber stopper was used to keep the turtle's mouth open during flushing. Stomach contents were collected in a screen strainer and placed in 10% formalin until processing. We conducted flushing on each turtle until we were reasonably sure that no more food would be obtained. To evaluate the efficacy of our flushing technique, we dissected three males after obtaining positive flushes and found that one individual had a minute quantity of filamentous algae adhered...