Study of Snake Populations in Central California

Abstract

At the San Joaquin Experimental Range in the dry, granite foothill area of central Calif., a total of 1126 snakes of 6 spp. were marked and released; 18.6% were recaptured one or more times after intervals up to 9 years. The rattlesnake (Crotalus viridis oreganus) was most frequently encountered, making up 60% of the records; the gopher snake (Pituophis c. catenifer). king snake (Lampropeltis getulus californiae.) and garter snakes (Thamnophis elegans couchii and T. ordinatus tetrataenia) were also found in substantial numbers. Rattlesnakes, gopher snakes, and king snakes tend to stay over periods of years in small areas; typical rattlesnake ranges are about 30 acres for males and 16 for females. Garter snakes wander more widely. Rate of growth and development varies greatly. Young rattlesnakes born in autumm avg. about 280 mm. head-and-body length; relatively few survive to an age of a year, and these may avg. 500 mm., with 4 rattles. At an age of 3 years they may have attained small adult size but usually require several years more to complete their growth. Adults gain approx. 1.5 rattles annually in males and 1.1 in females on the avg. Population density of rattlesnakes on a sample area was computed as 1.2 per acre, and of gopher snakes .3 per acre, and their toll of prey as at least 1.4 lbs. per acre, mainly rodent and rabbit. The ground squirrel (Citellus beecheyi) and cottontail (Sylvilagus audbonii) make up fully 85% of the prey weight, for the spring months at least. Food habits of several common predators were investigated and 7672 records of vertebrate prey items were obtained from them, of which 552 were snakes. The red-tailed hawk is a major snake predator on this area; 9.4% of the 4110 vertebrate food items recorded for it were snakes. The red-tailed hawk, horned owl, and coyote were all found to prey upon the gopher snake more frequently than upon the commoner but dangerous rattlesnake.