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) aff ects 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 r esult of hormonal manipulation, of ''neighboring'' males influences th ese effects. Field studies were conducted on four naturally isolated ' 'neighborhoods'' of lizards. Half of the males on three of the sites w ere randomly implanted with either saline or B, while on the fourth si te all males were implanted with B. Pre- and postimplant home-ranges a nd activity levels were determined. Home-range size and activity level were significantly reduced by corticosterone if normally aggressive s aline-implanted males were also present in the neighborhood. However, B had no effect on home-range if all males in the neighborhood were im planted 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 m ale home-ranges in a neighborhood remained unchanged after implantatio n. 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.