28th Annual Meeting and Symposium of the
Desert Tortoise Council, February 21-23, 2003
Abstracts

STUDENT PAPER

Reproduction of the Desert Tortoise (Gopherus agassizii) in Clark County, Nevada

Kimberly A. Goodwin¹, M. B. Saethre², T. C. Esque^1,2*, P.A. Medica³, R. Marlow², and C.R. Tracy^2
1U.S. Geological Survey, Western Ecological Research Center, Henderson, Nevada
²University of Nevada, Program in Ecology, Evolution and Conservation Biology, Biological Resources Research Center, Reno, Nevada
³U.S. Fish and Wildlife Service, Las Vegas, Nevada

Reproductive output of female desert tortoises was examined at three sites in the central Mojave Desert; Bird Spring Valley (BSV) from 1997 through 2002, Piute Valley (PV) from 1998 through 2002 and Cottonwood Cove (CWC) in 2001 and 2002. We used x-ray photography to determine clutch size, clutch frequency, egg width and total annual fecundity. We compared these reproductive parameters with winter annual plant production and winter precipitation to look for significant relationships that would allow us to predict reproductive output in future years. Tortoises at BSV produced more eggs per clutch than tortoises at PV; however, tortoises at PV had a higher frequency of clutches than tortoises at BSV. While these two populations employed different reproductive strategies, the outcome was that tortoises at both sites had similar annual egg production for all years. Large body size of tortoises at BSV may be responsible for the larger eggs that were found in this population compared with PV. Reproductive output of tortoises at CWC was unable to be accurately determined because of the difficulty of extracting tortoises from their caliche caves at this site.

Reproductive parameters were poorly correlated with annual plant aboveground biomass (with the exception of the number of eggs produced per gravid female at PV). Winter precipitation was significantly related to clutch frequency, percentage of egg-layers, and mean annual fecundity and thus was a better predictor of reproductive parameters.