EFFECTS OF CORTICOSTERONE ON ACTIVITY AND HOME-RANGE SIZE OF FREE-RANGING MALE LIZARDS

The purpose of our study was to examine whether corticosterone (B) affects the spacing behavior of free-ranging male side-blotched lizards (Uta stansburiana). Furthermore, we wanted to determine if the density, reflected in seasonal changes in population size, or behavior, as a result of hormonal manipulation, of ''neighboring'' males influences these effects. Field studies were conducted on four naturally isolated ''neighborhoods'' of lizards. Half of the males on three of the sites were randomly implanted with either saline or B, while on the fourth site all males were implanted with B. Pre- and postimplant home-ranges and activity levels were determined. Home-range size and activity level were significantly reduced by corticosterone if normally aggressive saline-implanted males were also present in the neighborhood. However, B had no effect on home-range if all males in the neighborhood were implanted with B. Space lost by B-implanted males was incorporated into the home-ranges of saline-implanted males so that the sum of all the male home-ranges in a neighborhood remained unchanged after implantation. These results suggest that elevated B levels put male lizards at a competitive disadvantage and, therefore, force these lizards to reduce their home-range. (C) 1994 Academic Press, Inc.