Additional Observations on Home Ranges and Longevity in the Lizard Sceloporus graciosus

Abstract

IN the summer of 1942, I marked a population of mountain swifts, Sceloporus graciosus, in a section of the Chaos Jumbles of Lassen Volcanic National Park, California. Individual lizards were rendered permanently recognizable by removal of toes in varying combinations. In 1942 and in subsequent years data have been gathered on this original group and additional lizards have been marked. In this way, it has been shown that the species at Lassen is of sedentary habits, individuals tending to remain for many years in relatively circumscribed areas, usually less than 100 feet in greatest dimension. This fact and others having to do with rate of replacement in the population, growth, and habits have been reported in previous papers ( Stebbins, 1944; Stebbins and Robinson, 1946). The present report records additional information relating to the fate of marked animals.' From August 6 to 10, 1947, in the area of study delimited in 1942, a total of 73 individuals was captured and then released. Of this number, 8 had been marked in 1942 and 10 in 1945. The remainder were unmarked. Persistent search of the area over a period of three months in 1942 brought to light 119 individuals exclusive of the season's young. Assuming a constant population size through the years, it is probable that 13 (11 per cent) of the original group was still present as based on the percentage of animals marked in 1942 among the random sample. In the same manner the number of individuals of the group marked in 1945 and still in the area may be roughly estimated. Ten of the 35 marked were recaptured. This number is approximately oneseventh of the random sample obtained in 1947. On the basis of probability, 17 individuals would be expected in the assumed total of 119, approximately 50 per cent of the original number. In 1945 it was estimated that one-third of the group marked in 1942 was present after a lapse of three years. Thus a decline to about one-half the number marked in 1945 after two years is reasonable. These estimates suggest that the number present in 1942 may have been halved during the first two years, was reduced to one-third the third year, and declined to about one-tenth by the fifth year. The rate of decline indicated is, of course, entirely a matter of speculation, since the actual number of individuals within the study area during these years was not known.