Effects of a spring snowstorm on behavior, reproduction, and survival of Belding's ground squirrels

Abstract

From 30 April to 26 May 1977 a snowstorm occurred in the Sierra Nevada [USA] where Spermophilus beldingi was being studied. The storm began 8 days after ground squirrels began emerging from hibernation. During the storm, emergence nearly ceased and mating was suspendend, body wt decreased sharply, locomotor abilities became impaired and nocturnal burrow sharing increased. The animals became more susceptible to predation and 1 case of intraspecific killing and cannibalism was observed. At least 4 animals starved; they were totally depleted of fat and had atrophied livers. During the storm, more adult females than males perished; 60% of females disappeared in 1977 vs. 32 and 26% in 1975 and 1976, respectively. When compared with 1975 and 1976, fewer 1977 females mated, conceived or weaned young. During 1969-1977 at Tioga Pass, 1st emergence of S. beldingi varied up to 6 wk with the animals emerging earliest in years of lightest snowpacks. At high altitudes where summers are brief, early emergence may increase the likelihood that young will reach appropriate body size before winter. Avoidance of the effects of unpredictable spring storms favors later emergence. In 1977, because of the snowstorm, late emergers were favored.