26th Annual Meeting and Symposium of the
Desert Tortoise Council, March 16-18, 2001
Abstracts

POSTER

Program Mark Survival Analysis of Tortoises Voiding their Bladders During Handling

Roy C. Averill-Murray
Arizona Game and Fish Department, 2221 W Greenway Road, Phoenix, AZ 85023

At the 1998 Symposium, I presented data that indicated that desert tortoises that voided their bladders during handling were less likely to be captured in subsequent years than those that did not void their bladders. This indirectly suggested that tortoises that void their bladders during handling have lower survival than those that do not void. A more conclusive analysis would measure survival directly. I accomplished this in an analysis using Program MARK. Data were taken from 3 monitoring plots (Eagletails, Granite Hills, and Little Shipp) and broken into 3 groups each: adult males, adult females, and juveniles (<180 mm MCL). Individual covariates included MCL at first capture and a binary voiding covariate for each year, 1990-94. About half the tortoises at Little Shipp voided their bladders at least once when handled, with lesser proportions at the other 2 plots. The most parsimonious model in the original candidate set of 21 models analyzed with Program MARK was one in which survival varied by MCL, plot, and voiding. Subsequent inclusion of an exploratory model that lacked the plot effect resulted in 49% greater support for the reduced model. Tortoises that voided their bladders during handling had significantly lower average annual survival (0.81-0.88) than those that did not void (0.96). Therefore, as suggested in 1998, researchers studying desert tortoises should develop well-defined study objectives that minimize handling time as much as possible in an effort to prevent tortoises from voiding their bladders.