Use of quaking aspen flower buds by ruffed grouse : its relationship to grouse densities and bud chemical composition

Quaking aspen (Populus tremuloides) staminate flower buds are an important winter food for Ruffed Grouse (Bonasa umbellus); however, use of these buds can vary among years. One explanation for this differential use of aspen flower buds is that the buds’ nutritional value or palatability changes. It has been proposed that fluctuations in the chemical content of aspen buds may affect their utilization by Ruffed Grouse, and that the utilization of aspen may be positively related to the population density these birds can maintain. This paper focuses on three key links of the above hypothesis: whether there are significant annual changes in the chemistry of aspen buds, ‘whether aspen utilization by Ruffed Grouse is mediated by the chemistry of the buds, and whether there is a correlation between aspen use and changes in grouse densities. We monitored chemical changes in aspen flower buds periodically over 11 years and related chemical changes to aspen use and Ruffed Grouse densities. Additionally, previous studies were re-examined to determine the relationship between aspen consumption and changes in grouse densities. Significant differences were observed in coniferyl benzoate and protein levels among years. Data suggest hat there may be inherent differences among aspen clones in their ability to chemically defend themselves. Use of aspen buds by grouse appears to be mediated by coniferyl benzoate and protein levels. Quaking aspen use was highly correlated to Ruffed Grouse densities. Lack of suitable or available aspen in the winter may increase predation risks and energetic costs for Ruffed Grouse.

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