Mid-winter activity budgets and diving behaviors of Harlequin Ducks (Histrionicus histrionicus) at Isle au Haut, Maine were examined. Feeding was the most frequent activity and the number of hours during the day devoted to feeding increased from December to March as day length increased. Resting was not a frequent mid-winter activity, but birds rested more in the morning than in the afternoon and the duration of resting bouts increased in March, likely in relation to increasing day length. During foraging bouts, first-winter males had longer submergence times and longer pause times than adult males, although the resulting dive:pause ratio was similar. This may be related to feeding inefficiency of the young birds or lack of experience with local habitats or prey species. Mean dive durations and pause durations at Isle au Haut were greater than reported elsewhere for this species, and may be related to strong local currents associated with the wave washed ledges on Isle au Haut.