Intra- and inter-seasonal variation in the socio-spatial behavior of adult male collared lizards, Crotaphytus collaris (Reptilia, Crotaphytidae)

When individuals maintain strong inter-seasonal philopatry to the same territories, males may be able to re-establish territory occupancy without intense intrasexual aggression, and instead spend more time courting females early in the reproductive season. Furthermore, when some males have prior experience defending the same territories, it may be necessary for young males to exhibit higher levels of aggression because they are establishing a territory for the first time. We tested these hypotheses by examining within-season (1992 and 1997) temporal variation in the social behavior of adult male collared lizards of known age and prior territorial experience in a population where inter-season philopatry to territories is high. Contrary to expectations, the frequency of aggression exhibited by males with and without prior territorial experience did not differ. The frequency of intra-sexual aggression was higher in 1992 than in 1997, perhaps because male competitors were more abundant in 1992. Although there was an interactive effect of year, male display and patrol were low at the beginning of the reproductive season in Apr. and May, reached peaks during midseason in June, and then decreased as reproduction ended in July. The size of territories showed a similar pattern, with males defending larger areas in June. Our data support the philopatry hypothesis in that the establishment of territories occurred without high levels of aggression early in the season, perhaps because territory boundaries have been well defined by high rates of patrol and advertisement during the middle of the previous season. Inter-sexual interactions were most frequent in June rather than at the beginning of the reproductive season. Adult females are producing their second clutches and yearling females are producing their first clutches in June. The high rate of inter-sexual encounters in June supports the hypothesis that males allocate more time to courtship when females are receptive because there are more reproductively active females at this time. The temporal pattern of activities in adult Crotaphytus collaris appears to function as a compromise between competing intra- and inter-sexual social demands on males, allowing males to maximize mating opportunities as well as maintain future access to productive territories.