Sex Ration and Age Structure in Two Red Squirrel Populations in Northern Saskatchewan

Abstract

Age determination, sex and age ratios of two red squirrel (Tamiasciurus hudsonicus) populations were studied in northern Saskatchewan from 1960 to 1966. Thirty red squirrels born in captivity to females caught at Cree Lake, Saskatchewan furnished lenses, femora, and humeri of known-age for establishing methods of determining ages of wild specimens. This study shows that the ages of red squirrels can be predicted with reasonable accuracy from lens weights and that juveniles and young adults can be distinguished from old adults by the appearance of the epiphyseal notches of humeri and femora. Sex and age ratios at Cree and Emma Lake were determined from 810 red squirrels collected by shooting and trapping. A complete population turnover of squirrels took place at Emma Lake in six years and at Cree Lake in nine years. The reduced longevity and greater mortality of squirrels at Emma Lake as compared with those at Cree Lake was attributed to heavier hunting and trapping pressure on the Emma Lake population. The sex ratios of 36 embryos, 23 young at birth, and 33 juveniles shot and trapped during July and August at Cree Lake was 0.92 males to 1.00 females. Contrary to statements of other workers, our data show an equal sex ratio in red squirrels at birth. The only sex ratio which differed significantly from unity was that of Emma Lake yearlings; this was attributed to the fact that juvenile males are easier to shoot or trap than are females.