The Present Status of the Garter Snake on Santa Catalina Island, California

Abstract

For 33 years, only two specimens of the garter snake (Thamnophis couchi hammondi) were recorded for Santa Catalina Island and the status of this species remained unknown. In August 1974, a small population was discovered in the stream and reservoir in Cottonwood Canyon. The species apparently occurs nowhere else on the island. Unlike most two-striped mainland specimens, garter snakes on Santa Catalina lack any pattern, being a uniform olive-brown with pale buff lips and chins. In this respect they most closely resemble a different species from central Baja California and a conspecific population near Lompoc on the California mainland. The ecology of Cottonwood and other stream canyons on Santa Catalina is discussed, as are human impacts on garter snakes, and recommendations for conservation measures. Finally, rafting is proposed as a mechanism by which garter snakes from the Lompoc region might have founded the population on Santa Catalina Island.