 2001 by the American Society of Ichthyologists and Herpetologists Copeia, 2001(2), pp. 521–525 Rates of Water Loss and Estimates of Survival Time under Varying Humidity in Juvenile Snapping Turtles (Chelydra serpentina) MICHAEL S. FINKLER Juvenile snapping turtles may be highly susceptible to dehydration during over- land movement because of their aquatic nature and large surface area to volume ratio. The present study examined the inﬂuence of body size and relative humidity on rates of evaporative water loss and estimates of survival time. Larger hatchlings had higher rates of evaporative water loss but longer survival times resulting from their greater absolute water contents. Rates of evaporative water loss decreased, and estimated survival times increased with increasing relative humidity. The ﬁndings suggest that evaporative water loss may be an important factor inﬂuencing survivor- ship and behavior during overland movements of juvenile snapping turtles. S NAPPING turtles (Chelydra serpentina) of var- ious age classes are known to make exten- sive overland migrations as part of their repro- ductive behavior (reviewed in Ernst et al., 1994) as well as in response to detrimental en- vironmental conditions such as drought or food shortage (Gibbons et al., 1983; Parker, 1984; Yeomans, 1995). However, snapping tur- tles, like other highly aquatic turtles, may be particularly prone to dehydration during these overland forays as a result of relatively high rates of evaporative water loss (Schmidt-Niel- sen and Bentley, 1966; Ernst, 1968; Chessman, 1984). High rates of water loss may be espe- cially problematic for neonatal and juvenile snapping turtles by virtue of their relatively high surface area to volume ratio. Thus, the body water content of the animal and the rate of evaporative water loss together may mark- edly inﬂuence the ability of the juvenile snap- ping turtles to complete prolonged overland migrations. Although the effects of variation in body size and water content on the desiccation tolerance of neonates have been preliminarily examined in one study (Finkler, 1999), the in- ﬂuence of environmental factors (e.g., relative humidity, temperature, convection) on evapo- rative water loss and desiccation tolerance has yet to be examined. The present study examined the inﬂuence of relative humidity and body size on rates of evaporative water loss and desiccation toler- ance of yearling snapping turtles. The amount of time the turtle can survive without rehydra- tion should increase with increasing relative humidity because of reduced rates of water loss. Moreover, larger juveniles, with their larg- er absolute water contents and relatively small- er surface areas to volume ratios, should be able to survive longer out of water than can smaller juveniles. MATERIALS AND METHODS The juvenile snapping turtles used in this study were reared from eggs from four clutches collected in Washtenaw County, Michigan, on 1 June 1998. The eggs ranged from 10.157–13.602 g in mass (mean = 11.560 g). Eggs from each clutch had been half buried in moistened ver- miculite (0.5 ml H 2 O/g dry vermiculite, with a water potential of about -325 kPa) and incu- bated in a pair of Hova Bator 2362N incubators (GQF, Inc.) at 25 C. Eggs hatched over a four- day period between 17 and 20 August 1998. Hatchlings were housed in plastic shoeboxes ﬁlled with water to approximately 5 cm in depth. Animals were induced to hibernate, be- ginning on 15 November 1988, by lowering their temperature from 25 C to 5 C over 30 days with a change of 0.7–0.8 C daily. They remained at 5 C until 15 February when the temperature was raised 0.7–0.8 C per day until 15 March. Otherwise, animals were maintained at 25.0 C on a 12:12h L:D photoperiod and fed commer- cial catﬁsh feed ad libitum three times per week. Testing of the animals was conducted be- tween 16 May and 17 June 1999. At the time of testing (approximately nine months posthatch- ing), turtles varied considerably in size, ranging from 27.4–40.6 mm in carapace length and 6.019–15.999 g in initial body mass. Differences in size appeared to result primarily from differ- ences in feeding, because preliminary analyses found neither measure of body size at nine months to be signiﬁcantly inﬂuenced by either initial egg mass or clutch. To determine the water and solid contents of fully saturated individuals prior to dehydration, 12 randomly selected animals were sacriﬁced and their carcasses dried to a constant mass at 60 C. Another 10 animals were used for deter-