Interactions of humans and bald eagles on the Columbia River estuary.

Human activities have had profound effects on bald eagle (Haliaeetus leucocephalus) populations. Few experimental studies exist that address the effects of human activities on foraging eagles during the breeding season. Information from these types of studies is needed so that resource managers can allow humans and eagles to coexist. We investigated the response of breeding bald eagles to human activities in foraging areas on the Columbia River estuary, Washington-Oregon, during spring and summer, 1985 and 1986. We distinguished between 2 forms of interaction. In the first, a moving human approached a stationary eagle and induced a disturbance. This type of interaction was rare on the Columbia River estuary and accounted for a minor proportion of an eagle's time-energy budget. Only 20% of all moving human activities observed during this study resulted in human-eagle encounters within 500 m, and <6% of all encounters resulted in a visible disturbance to an eagle. In the second form of interaction, an eagle had a choice of alternative foraging sites, some of which may have had human activities occurring nearby. In this situation, the eagle had the freedom to choose a destination, given the pattern of human activities. This type of interaction represented the major form of human-eagle interaction on the Columbia River estuary. To investigate this, we studied 6 pairs of eagles in each of 2 years; each pair was sampled 3 times during the breeding season, corresponding to incubation, nestling, and postfledging stages of the nesting cycle. Each sample consisted of a 3-day control period, during which we monitored "normal" eagle activity patterns, and a 3-day influence period, during which we "disturbed" (i.e., stationary boat with observer) a high-use foraging area. We compared eagle activity patterns within 1,200 m of the experimental disturbance between