Twenty-Third Annual Meeting and Symposium of the
Desert Tortoise Council, April 3-5, 1998
Abstracts

Nitrogen may be a limiting resource for the production of eggs by female desert tortoises. We evaluated the influence of dietary nitrogen intake upon reproductive output in Spring 1996 by: 1) measuring the food and nitrogen intakes (g dry) of 24 females fed six pelleted diets (i.e., four females per diet; 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 % N, DMB; all diets contained 0.4% potassium), 2) detecting ovulation and shell formation using ultrasonagraphy, and 3) measuring clutch size (number of eggs per clutch) using radiography. Some females ovulated and formed eggshells before consuming much diet during the spring. Dietary treatments did not affect the hatching success of incubated eggs but showed a significant effect upon the number of eggs produced per female. Many measures of reproductive output (e.g., size of first clutches) were correlated to body mass but not to food or nitrogen intakes. Egg mass (fresh or dry), water content, and composition (dry mass of yolk, white, or shell) were not affected by dietary treatment or correlated to female body size, food intake, or nitrogen intake. Ten of the 24 females were fed their respective diets through another reproductive cycle (until July 1997). The number of eggs that they produced in the second reproductive season was correlated to female body size and their nitrogen intake since Spring 1996. Remarkably, four of six additional females that were fed the lowest N diet (0.5 % N) from July 1996 to July 1997 still managed to produced eggs in 1997.