Optimal egg incubation temperature, and the effects of diet on growth of hatchling Eastern Indigo snakes (Drymarchon couperi) during a captive head-start program
Type of Degreethesis
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Optimal husbandry techniques are desirable for any headstart program, but frequently are unknown for rare species. In this thesis I determine the optimal incubation temperature and optimal diet diversity for eastern indigo snakes (Drymarchon couperi) grown in a laboratory setting. Optimal incubation temperature was estimated by determining the relationships between temperature and two variables dependent on temperature: shell dimpling, a surrogate for death from fungal infection; and deviation of an egg from an ovoid shape, a surrogate for death from developmental anomalies. Based on these relationships I determined the optimal incubation temperature to be 25 °C for D. couperi eggs. Additionally, I used incubation data to assess the effect of temperature on duration of incubation and size of hatchlings. Because Drymarchon couperi has few relevant data describing hatchling diets necessary to achieve optimal growth, I examined growth rates of captive snakes fed known diets. Feeding data were examined over a two-year period for 130 hatchling Drymarchon couperi. These snakes exhibited a negative linear relationship between total mass eaten and growth rate when fed less than 1711 g over their first 21 months and displayed constant growth for individuals exceeding 1711 g over that time period. Similarly, growth rate increased linearly with increasing diet diversity up to a moderately diverse diet, followed by constant growth for higher levels of diet diversity. Of the two components of diet diversity, number of genera consumed, and evenness of diet items consumed, diet evenness played the stronger role in explaining variance in hatchling growth. These patterns document that my goal of satiating the snakes was achieved for some individuals but not others and that diets in which total grams consumed is distributed equivalently among the genera that a snake is willing to consume yields the fastest growth rates for that individual.