Foraging Behavior and Habitat Distribution of Seabirds on Fourth of July Beach and South Beach, San Juan Island

Abstract

Seabirds play an important role in the ecosystem by being one of the top predators of the marine food chain, and also as bioindicators of environmental changes. Their ability to quickly respond to their surroundings can be useful in anticipating possible threats not only to the seabirds but also to areas where they congregate. This study aims to assess foraging behaviors and habitat distribution of four species groups; loons, ducks, grebes, and gulls, found at two representative beaches (Fourth of July Beach and South Beach). Marine bird surveys and habitat assessments were conducted to see which factors, mainly time of day, tide state, prey abundance, and weather, affect the number of foraging birds and their distribution. It was found that there were no significant differences in the numbers of foraging birds at any time of the day at Fourth of July Beach, while more birds were foraging in the early morning at South Beach. Marine birds were also observed to be scattered both nearshore and offshore on Fourth of July Beach, while the birds in South Beach preferred either nearshore (gulls and grebes) or offshore (loons and ducks). Our habitat assessments imply that prey abundance mostly influenced the patterns seen for foraging birds by time of day and their spatial distributions. Information in this study could be used as guidance for conservation and management, to further protect the seabirds and their preferred habitats.