Frequencies of Broken Tails among Uta stansburiana in Southern Nevada and a Test of the Predation Hypothesis

Abstract

Frequencies of broken tails among hatchling (1-4 months), yearling (7-12 months) and 2-year old Uta stansburiana (19-24 months) in southern Nevada were examined for the years 1966-1973. Frequencies among males and females in the two older age groups did not differ significantly. The frequency of broken tails in hatchlings (0.06) was lower than that in yearlings (0.30), which was, in turn, lower than that in 2-year old Uta (0.51). Break frequencies among yearlings varied from 0.26 to 0.37 in different years, while frequencies among 2-year olds varied from 0.33 to 0.64. These differences were not statistically significant. Among hatchling Uta, tail break frequencies ranged from as low as 0.029 (1971) to as high as 0.099 (1966), and differences between years were highly significant. Tail break frequencies in all age groups were analyzed in terms of spring densities of Uta and of an important predator (Crotaphytus wislizenii). Tail breaks in yearling and 2-year old Uta were not correlated with either density variable. Tail-break frequencies of hatchling Uta were significantly correlated with predator density (r = 0.88), and multiple regression analysis (with densities of both lizards as independent variables) yielded an R2 of 0.80. This is the first test of the tail break