Grouse Abundance and June Temperatures in Wells Gray Park, British Columbia

Abstract

A study of weather records and the annual grouse kill in Wells Gray Park, British Columbia, showed a relationship between June weather and the fall kill. A positive correlation coefficient of 0.913 was found to exist between the fall grouse kill and the mean maximum June temperature. The grouse involved were chiefly ruffed grouse (Bonasa umbellus). It seems apparent that high temperatures in late spring and early summer are an important factor in the reproductive success of grouse. This study was undertaken to explore the possible relationship between weather and fall grouse populations in Wells Gray Park, British Columbia. It was hoped that the results might be useful in forecasting population trends as well as in contributing to knowledge of the ecology of the species. Field observations for a 10-year period in Wells Gray Park suggested to the writ- ers that warm weather in spring and early summer is associated with high populations of ruffed grouse in the fall. Two sets of data were used to test this hypothesis: (1) weather data for the park, compiled regularly at Park Headquarters for the Government of Canada, and (2) records kept since 1952 of all game species killed in the park. Records of the annual grouse kill were assumed to give at least a rough indication of fall population levels. Grouse are not abundant in the park and are usually killed along roads and trails by hunters seeking big game. A few local people hunt grouse for sport. Bag limits and length of hunting season varied during the study period, but these variations do not seem to have af- fected the kill. Few hunters obtained bag limits anyway, and most grouse were killed before November 1, even though the sea- son was in some years extended beyond that date. Hunters have shown repeatedly that they cannot distinguish among the three most common species of grouse in the park -ruffed grouse, spruce grouse (Canachites canadensis), and blue grouse (Dendraga- pus obscurus)-so all grouse are included in figures showing the annual kill. We esti- mate that approximately 85 percent of the annual kill consists of ruffed grouse, with little variation through the years. This esti- mate is based on both our own hunting ex- perience and the contents of hunters' bags which we were able to examine. June weather was more closely linked to the fall kill than was May or April weather. The mean maximum daily temperature for the month was found more significant in relation to kill data than were other mean