Eye Lens, Testes, and Body Weight Trends in Alberta Red Squirrels

Criteria are presented for 3 methods for age separation of red squirrels (Tamiasciurus hudsonicus) in Alberta: eye lens weight, testes weight, and body weight. After an initial 5-6 months of rapid growth, each lens increased about 2-3 mg per year. Monthly testicular weights of subadults were below those of adults. Increase in body weight of young squirrels was similar, about 10.7 g per week, in both sexes and nearly linear between ages of 3.5 and 16 weeks. Body weights of adult red squirrels varied with individual, sex, season, habitat, and latitude. At Rochester, Alberta, weights recorded for live adults varied from 170 to 254 g. Male weights began to increase in January and peaked in April (x̄ = 226 g); female weights began to increase in April and peaked in June (x̄ = 226 g). Mean weight (193 g) of squirrels residing in quaking aspen (Populus tremuloides) forests was less (P < 0.0001) than those, 208 and 215 g, respectively, of squirrels residing in spruce (Picea glauca and P. mariana) and jack pine (Pinus banksiana) forests. Body weights of red squirrels increase from low (x̄ = 188 g at 42°) to high latitudes (x̄ = 259 g at 65°).