Arctic National Wildlife Refuge. The refuge supports a greater variety of plant and animal life than any other protected area in the circumpolar arctic. There is a continuum of six different ecozones spanning some 200 miles (300 km) north to south. Along the northern boundary of the refuge, barrier islands, coastal lagoons, salt marshes, and river deltas provide habitat for migratory waterbirds including sea ducks, geese, swans, and shorebirds. Fish such as dolly varden and arctic cisco are found in nearshore waters. Coastal lands and sea ice are used by caribou seeking relief from biting insects during summer, and by polar bears hunting seals and giving birth in snow dens during winter. The arctic coastal plain stretches southward from the coast to the foothills of the Brooks Range. This area of rolling hills, small lakes, and north-flowing, braided rivers is dominated by tundra vegetation consisting of low shrubs, sedges, and mosses. Caribou travel to the coastal plain during June and July to give birth and raise their young. Migratory birds and insects flourish here during the brief arctic summer. Tens of thousands of snow geese stop here during September to feed before migrating south, and musk oxen live here year-round.