Population Ecology of Blunt-Nosed Leopard Lizards in High Elevation Foothill Habitat

Abstract

We captured 1078 Blunt-Nosed Leopard Lizards (Gambelia sila) 2396 times between 1989 and 1994 on the Elkhorn Plain, San Luis Obispo County, California. Based on size at first capture, we caught 119 adult (� 90 mm snout-vent length (SVL)) and 430 hatchling/juvenile (<90 mm SVL) males, and 139 adult and 390 hatchling/juvenile females. Sex ratio of males to females was 1.04 (549 males/529 females). Adult G. sila generally became active in April, and activity remained relatively high into July. Hatchlings were first noted in either July or August and generally could be found until early November, except in 1990 when no hatchlings were found at any time. Mean number of adults and hatchlings found active each day differed significantly across years, but as many as 32 adults and 42 hatchlings were seen on a plot during a census. Estimates of population abundance on a plot also varied yearly from 20-164 adults and 0-273 hatchling/juveniles and seemed to be affected either by too little or too much rain. Differences in daily activity varied and were moderately well explained by environmental factors. We estimated survivorship of lizards and found 29.0% of hatchlings from 1992 survived to 1993, and 14.6% of hatchlings from 1993 survived to 1994. The oldest G. sila found was a female estimated to be 4 years, 10 months when last caught, although most adults were not seen after 2 yr. Growth of individuals varied by year: highest growth rates were for lizards that hatched in 1991 and 1992, and lowest growth occurred in lizards that hatched in 1989. We found adult leopard lizards with eggs in all years but 1990. Females generally were gravid by late April or early May, and some females were found with eggs in early July. Female size at first reproduction was about 90 mm SVL, clutch size ranged from 1-6 eggs, and overall mean clutch size regardless of year or clutch order was 3.4 eggs. Many females produced multiple clutches in a year, and we found up to four clutches by a single female.