One of the largest land mammals in the United States, the Grizzly Bear, is also endangered in Washington, Montana, Idaho and Wyoming. According to the Brown Bear website, the grizzly bear population decreased from 100,000 in the 19th century to less than 1,000 in 1975. The website also states that the Selkirk Mountains -- which spans into Northeast Washington -- only has 10 grizzlies.
The endangered sei whale runs past the shores of Washington during its migration seasons, which usually occurs in the summer. This whale is one of the largest baleen whales, or great whale, in the world with an approximate length of 66 feet. In the 1950s, the estimated number of sei whales was 42,000. They received protection from whalers in 1976 at which time their population was 8,600.
Leatherback sea turtles are marine reptiles and they frequent the coastlines of Washington and Oregon. Unlike other turtle species, leatherbacks have skin on their backs, not bony shells. Leatherback sea turtles grow up to nine feet long and migrate from the Pacific Northwest to Indonesia. According to Ecotrope, only an estimated 2,100 leatherbacks live in the Pacific Ocean, as of February 2011. Western pond turtles are an endangered species in Washington State, but not protected by the Endangered Species Act. The causes of their endangered status, according to the University of Washington, include disease and habitat loss. Also, these turtles have a slow reproduction period; females only lay 3 to 13 eggs per year. Adult western pond turtles grow up to eight inches.
The northern leopard frog has a widespread population throughout much of the United States -- it is the official state frog of Minnesota and Vermont -- but is endangered in Washington State. These frogs used to be spotted frequently throughout Washington. However, they are extinct in every region except Moses Lake, located in the central region of the state. The population range of Oregon spotted frogs is Oregon, Washington and British Columbia, Canada. These frogs used to be in Northern California, but are no longer found there. According to the Vancouver Aquarium, the decrease in Oregon spotted frogs is due to loss of habitat and introduction of invasive species.
The northern spotted owl is a subspecies of the spotted owl. The U.S. Fish and Wildlife Service and the Washington Department of Fish and Wildlife consider this bird species endangered. When it matures, the northern spotted owl is approximately 19 inches in length and has a wingspan of 42 inches. According to the Palouse Audubon Society, the upland sandpiper is nearly extinct in the state of Washington. However, this species is not extinct in other regions of North America. Population decreases are the result of hunting and loss of habitat.