Male Territoriality and the Mating System of Richardson's Ground Squirrels (Spermophilus richardsonii)

Abstract

Richardson's ground squirrels ( Spermophilus richardsonii ) were observed at two localities in Alberta, Canada. Most males emerged from hibernation before any of the females. Dominant males were territorial and defended core areas (the area in which they spent 80% of their time) that encompassed the emergence sites of several females, so that the mating system can be characterized as male defense polygyny. Subordinate males were non-territorial and ranged widely during the breeding period. At Highwood River study area (HRSA), where the operational sex ratio (OSR) was extremely male-biased because the persistence of snow cover produced an asynchronous and patchy emergence of females, over half the resident males were non-territorial. By contrast, territoriality was more evident at Roi Lakes study area (RLSA), where the higher density and greater synchrony of female emergence caused the OSR to be less male-biased. Resident males at RLSA spent proportionately less of their aboveground time feeding, and spent more time moving about, being vigilant, and interacting agonistically than males at HRSA. These results support the hypothesis that when females are mating, the OSR is an important influence on the behavior of males. Dispersal by some males occurred before, during, or after the breeding period, though some males continued to reside in areas they occupied during the breeding period. In successive breeding seasons adult males were found in the same general vicinity. Our study demonstrates considerable intraspecific variation in the behavior of male Richardson's ground squirrels, which belies classifications of sociality that treat behavior as being species-specific.