29th Annual Meeting and Symposium of the
Desert Tortoise Council, February 20-23, 2004
Abstracts

STUDENT PAPER

Apparent Female Choice in a Population of Desert Tortoises in the Central Mojave Desert, California

Mark Massar
Charis Corporation, Directorate of Public Works, Environmental Division, Building 602, P.O. Box 105097, Fort Irwin, California 92310

In 2003, I began the first field season of a study investigating apparent female choice at a remote study site on Fort Irwin. This project is part of a larger multi-year study, conducted by the USGS-BRD, to explore tortoise social behavior in an area free from human impacts. Understanding female choice is important in deciphering the social structure of this population. The specific question that is being explored is whether female desert tortoises in this population show a preference to mate with particular male tortoises. Do female tortoises elicit courtship from certain male tortoises, while actively rejecting the advances of other male tortoises?

I tracked 6 female tortoises, fitted with radio transmitters, at a study site on the eastern border of Fort Irwin. Observations were done over a total of 38 days between late July and early October. This period corresponds to the peak of mating activity when male testosterone levels are at their highest. The recording methods used included a combination of behavior sampling in conjunction with focal sampling. Behavior was divided into clearly defined categories based on information from previous behavioral studies at the study site (USGS), a published ethogram based on desert tortoises in semi-natural conditions (Herpetological Monographs, No. 8), and information gathered during a preliminary observation period. Behavioral patterns that likely indicated female acceptance or rejection were used (e.g., coming out of coversite for a courting male, continuously turning shell away from the advancing male, dropping shell tightly to the ground, quickly seeking refuge under a bush or coversite, lifting shell up for a courting male, etc.).

I observed few actual matings. There were many instances when a male and female were located close together, but were apparently unaware of each other. Other times, two individuals associated with each other for extended periods (sometimes days), but no mating took place while I observed.

Often times, a female tortoise remained in her coversite while a male courted her at the cave's entrance. Because males are generally much larger than females, females can select caves too small for males to enter. The best the male could hope for in this situation is for the female to accept his advances and come out of her cave. This would be a clear sign of female choice, and I've observed this on occasion.