Because of environmental and topographical contrasts on San Juan Island, you’ll find a surprising variety of wildlife here: Large marine mammals such as Orca whales, Dall’s porpoises and Pacific Harbor seals; terrestrial mammals such as red fox and Columbia blacktail deer; bats; reptiles; amphibians; more than 200 species of birds; 32 species of butterflies; 200 species of fish; and hundreds of species of marine invertebrates. Many species reside at San Juan Island NHP or in its surrounding waters year around, some are summer or winter residents, and others visit the island to rest and feed during seasonal migrations.

Island biogeography explains why there are fewer species of animals on San Juan Island than on the neighboring mainland: they must find a way to cross seven to 20-miles stretches of open water or vast expanses of open sky.

Not all animal species are native. Some, such as the red fox, European rabbit, and Norway rat, were introduced to the island by humans, which changed the island’s natural balance. The future of all these species is intricately tied to the environmental health of the land, water, and air of San Juan Island National Historical Park, the Straits of Juan de Fuca, Georgia, Haro, and beyond.

http://science.nature.nps.gov/im/units/nccn/SpeciesSelect.cfm