In the Strait of Juan de Fuca, the two most important sites are Smith and Protection islands. Both are composed of glacial deposits and heavy sod that has developed under dense grassy vegetation (Fig. 7). Consequently, these two islands support most of the burrowing seabirds in the region. Unfortunately, both islands have historically been subjected to much human disturbance (Richardson 1961; Manuwal 1974).
The existing information on seabird colonies in both the coastal and San Juan Island areas has been largely derived from aerial surveys by the U.S. Fish and Wildlife Service. These surveys are inherently biased toward surface-nesting species such as gulls and cormorants. Population estimates for guillemots, auklets, storm-petrels, and puffins are less accurate. Some additional information obtained by direct island visitation has been provided by Kenyon and Scheffer (1961), Richardson (1961), Thoresen and Galusha (1971), G. Eddy (unpublished data), and D. A. Manuwal (unpublished data). Although other accounts of Washington seabirds are available, the references listed above are specifically oriented toward population assessment.
Olympic Peninsula
Despite the large number of offshore rocks, islets, and islands along the Pacific coast of Washington, significant seabird colonies are present only on about 30 islands. Since Table 5 summarizes the population estimates for 12 species of seabirds breeding on 24 major sites, it represents only the majority and not the total number of breeding seabirds on the Pacific coast of Washington. About 74% of the entire Washington seabird population resides on the coastal rocks and islands.
Major colony sites with more than 2,500 breeding pairs are Grenville Arch, Willoughby Rock, Destruction Island, Cake Rock, Carroll Island, and Bodelteh Island. More intensive censusing, especially of nocturnal burrowing species will undoubtedly raise the population estimates for these and other islands off the coast. About 54% of the total coastal population is composed of the common murre and rhinoceros auklet.
Fig. 5. Photograph of Destruction Island off the coast of Washington.
Fig. 6. Map of the San Juan Archipelago showing sites of major seabird breeding colonies: 1—Viti Rocks; 2—Colville Island; 3—Smith Island.