Predation on nests and weight change in eggs an indication of their moisture requirement during the nest period were measured as. Both factors may explain habitat selection and breeding density of hens. From 1994 through 1996, three chicken eggs were placed in each of 13 old nest sites of grouse, and in 20 possible nest sites 100 m apart along a line in each of four forests with different densities of grouse. Forests and estimates of breeding density (km?) of spruce grouse Dendragapus canadensis and ruffed grouse Bonasa umbellus, respectively, were: young jack pine Pinus banksiana 0,2; medium-aged pine 35,0; old pine 9,0; and old mixed-forest Populus tremuloides and Abies balsamea 0,18. Total egg loss in line nests (N = 59-61) ranged from 10 to 25%. Old nests (N = 38) had a total loss of 42%. Nest loss (N = 68) was apparently caused by red squirrel Tamiasciurus hudsonicus 50%, black bear Ursus americanus 37%, and corvids and red fox Vulpes vulpes 10%. There was no apparent correlation between density of either grouse and predation in each year and forest. Nest loss was greatest (42%) where spruce grouse were most abundant and low and similar (20,23%) where ruffed grouse were low and most abundant. However, mean change in weight of eggs varied significantly between forests and years. Change in mean weight for each forest ranged from a loss of 0.4 g to a gain of 1.3 g. Egg weight changes in old nests were similar to egg weight changes in line nests in the same forest suggesting line nests were representative to actual nests. Based on weight change of eggs, forests were wet, wet/dry, moist, and dry. Most spruce grouse lived in wet forest (medium-aged pine) and most ruffed grouse in dry forest (old mixed-forest). Few of either species inhabited wet/dry forest (old pine) and moist forest (young pine). I infer that eggs of spruce grouse are in wetter sites than those of ruffed grouse. The habitat selection and density of both may be partly explained by the moisture requirement of their eggs.
Key words: Bonasa umbellus, boreal forests, Canada, Dendragapus canadensis, egg moisture requirements, egg weight, nest predation, Ontario, ruffed grouse, spruce grouse
James F. Bendell, University of Toronto, RR 2, Clayton, Ontario, K0A 1P0, Canada