Feeding trials.showed that ruffed grouse (Bonasa umbellus) performed well on diets containing 20% Christmas hollyfem (Polystichum acrostichoides) or mountain laurel (Kalmia latifolia), but diets containing 40% of these forages resulted in lower protein and energy intake and the Christmas hollyfem diet caused a loss of body mass. Grouse were not able to maintain themselves solely on evergreen leaves. Glucuronide excretion was greatest for the 40% mountain laurel diet. Ornithine conjugate excretion was greatest for a diet with 40% deciduous leaves. Sulfate excretion did not vary among diets. Intake rate of leaves was an asymptotic function of bite size when the density of bites did not limit intake. Intake rate of leaves decreased at plants densities < 322 plants/m2. The maximum intake rate of leaves was 25% of the intake rate of aspen buds observed in wild grouse (Huempfuer and Tester 1988). Intake rate of raisins was an asymptotic function of bite size and was 20 times greater than the intake rate of leaves. Ruffed grouse in the Southeast must forage for> 100 min/day under ideal conditions to satisfy energy requirements. / Ph. D.