Located well above the Arctic Circle, the site includes the mountainous Wrangel Island (7,608 km2), Herald Island (11 km2) and surrounding waters. Wrangel was not glaciated during the Quaternary Ice Age, resulting in exceptionally high levels of biodiversity for this region. The island boasts the world`s largest population of Pacific walrus and the highest density of ancestral polar bear dens. It is a major feeding ground for the grey whale migrating from Mexico and the northernmost nesting ground for 100 migratory bird species, many endangered. Currently, 417 species and subspecies of vascular plants have been identified on the island, double that of any other Arctic tundra territory of comparable size and more than any other Arctic island. Some species are derivative of widespread continental forms, others are the result of recent hybridization, and 23 are endemic.