Chelydra

Abstract: Road mortality has the potential to alter the structure of turtle populations because turtle popula- tions are highly sensitive to additive sources of adult mortality. To address the issue, we captured painted turtles ( Chrysemys picta; n = 174) and snapping turtles ( Chelydra serpentina; n = 56) in 18 wetlands surrounded by low road density (≤1.5 km roads/km 2 of landscape) and 17 wetlands surrounded by high road density (>1.5 km/km 2 ) in central New York in 2002. High road density was associated with male-biased sex ratios in painted turtles (74% vs. 54% males; p = 0.01) and snapping turtles (95% vs. 74% males; p = 0.08), whereas turtle morphology and abundance were not associated with road density. Disproportionate road mortality of females on nesting migrations is the most likely cause of skewed sex ratios.

Abstract: Flexible-shelled eggs of common snapping turtles (Chelydra serpentina) were incubated on two substrates (sand and vermiculite) at each of three temperatures (26.0°, 28.5°, 31.0°C) and three moisture regimes (water potentials initially -150 kPa, -550 kPa, -950 kPa) in a factorial experiment assessing the influence of these variables on the water relations of eggs and the development of embryos. Hatching success was high on wet substrates at 26.0° and 28.5°, but declined at the highest temperature and on drier media. Net absorption of water by viable eggs, duration of incubation by embryos, and size of hatchlings were positively correlated with wetness of substrates and negatively correlated with temperature. Turtles hatching from eggs at 26.0° were males regardless of the wetness of the medium, whereas those emerging from eggs at 28.5° and 31.0° were females. These patterns of response characterized eggs incubated on sand as well as those on vermiculite. Findings from this study indicate that temporal and spatial variations in moisture and temperature within and among natural nests probably elicit ecologically important variation in size and sex of hatchling snapping turtles.

Abstract: Reproduction of snapping turtles was studied from 1978-1983 and nesting ecology and demography of hatchling snapping turtles were studied from 1976 through 1982 in south- eastern Michigan. The plastron lengths of reproductive females varied from 159-235 mm. Mean clutch size over 6 yr was 27.9 eggs (range = 12-41) and showed a significant positive linear rela- tionship with body size of females. Females produced only one clutch per year. The youngest known-age, reproductive female was 12 yr of age. Duration of the nesting season varied from 13- 31 days, and the initiation date varied by 22 days (22 May-12 June). The beginning of nesting activity each year was significantly correlated with the amount of heat available during March, April and May. Daily nesting activity was essentially bimodal with a major peak occurring between 0600 and 1100 h and a lesser peak of activity between 2000 and 2300 h. Nest construction averaged 111 min. Body temperatures of females at the time of nest completion ranged from 20.4-28.0 C (x = 22.9 C). Nests averaged 183 m straight-line distance from the nearest relatively permanent water, and no significant difference was found between the distances from water of those nests destroyed by predators and those escaping predation. Females nested in open areas that were adjacent to their marsh of residence or adjacent to other bodies of water. Observed females moved as far as 1625 m (straight-line distance) in preparation for nesting. Some females that were observed nesting in more than 1 yr constructed nests within 5 m of a previous nest, whereas other females changed nesting areas and constructed nests up to 1000 m apart. Predation rates on nests averaged 70% and ranged from a high of 100% in 2 yr to a low of 30% in 1 yr. The majority of nest predation occurred within 24 h of nest construction. The major predators were raccoons and foxes. Nests preyed upon by foxes were significantly older and further from water than nests destroyed by raccoons. An average of 4.14 eggs or developing embryos died in nests that escaped predation. Weekly mean tempertures in exposed and shaded nests ranged from 17.2-23.3 C during the entire incu- bation period. Nest temperatures were significantly lower in the shaded nest for all weeks except the first week following egg laying. These data indicate that shaded nests do not provide enough heat to allow complete development. Dates of hatchling emergence ranged from late August to early October, with the majority of emergence occurring in September. The average number of days from egg laying to hatchling emergence was 93.2. All sources of mortality resulted in a probability of 0.22 of surviving from age zero to age 1 (an approximately 90-day period from egg laying to hatchling emergence from the nest).

Abstract: Eggs of the common snapping turtle, Chelydra serpentina, were incubated at constant temperatures ranging from 20°C to 30°C, At hatching, the oviducts were absent or incomplete in males; the testes were differentiated. In females at hatching, the oviduct was intact hut in some cases the gonad retained bisexual characteristics. Three months after hatching, the ovary was differentiated and contained follicles. Eggs incubated at 20°C and at 30°C developed into females in 100% of the cases. At 26°C, 99% of the individuals were males; at 24°C, 100% were males. More males than females developed at incubation temperatures of 22°C and 28°C.