Food limitation and habitat preference of northern flying squirrels (Glaucomys sabrinus) and red squirrels (Tamiasciurus hudsonicus) were examined in British Columbia, Canada. Using mark-recapture techniques to estimate population demographics, we tested the hypotheses that populations of G. sabrinus and T. hudsonicus were limited by availability of food and that old-growth stands provided higher-quality habitat than second-growth stands. Populations were monitored on six study areas; two second-growth lodgepole Fine (Pinus contorta) stands (controls), two second-growth pine stands with food supplementation (treatments), and two old-growth lodgepole Dine stands. Sunflower seeds were applied (20 kg ha(-1) month(-1)) to treatment stands by helicopter in a uniform distribution for 3 summers, and mark-recapture of G. sabrinus and T. hudsonicus was initiated in the second summer of food supplementation. There were significantly more G. sabrinus and T. hudsonicus in treatment stands than in control stands. The mean density of G. sabrinus and T. hudsonicus in treatment stands was ca. 1.8 times greater than that in control stands, Estimates of population sizes for G. sabrinus in control stands were significantly lower than these in old-growth stands, Estimates of population sizes for T. hudsonicus in control and old-growth stands were not significantly different, Adult male G. sabrinus in control and treatment stands were significantly heavier than these in old-growth stands. Body mass for T. hudsonicus us and the proportion of adults breeding, recruitment, and survival rates for G. sabrinus and T. hudsonicus did not vary among control, treatment, and old-growth stands, Consequently, populations of G. sabrinus and T. hudsonicus appeared to be limited by availability of food, but individuals did not appeal to benefit from food supplementation, Second-growth stands were not suboptimal habitat for G. sabrinus and T. hudsonicus.
