Central American squirrel monkeys, mantled howler monkeys, both two-toed and three-toed sloths, agoutis, giant anteaters, great curassows, black hawks, spectacled owls, hummingbirds, 220 species of butterflies, golden orb spiders, otters and raccoons. Four species of sea turtle (green, Pacific ridley, hawksbill, and leatherback) nest on the beaches. The abundance in wildlife can in part be explained by the variety of vegetation types, at least thirteen, including montane forest (which covers more than half the park) cloud forest, jolillo forest (palm swamp), prairie forest, alluvial plains forest, swamp forest, freshwater herbaceous swamp and mangrove, together holding over 500 tree species, including purple heart, poponjoche, nargusta, banak, cow tree, espave and crabwood. The high biodiversity can also be attributed to Costa Rica's position on a north-south corridor for flora and fauna; part of the "land bridge" and wildlife corridor that links the large continents of North America and South America. In 41,800 hectares, Corcovado houses 3% of the world's biodiversity. National Geographic Society defined it as the most biologically intense place in the world. The waters of the park are calm and rich in biodiversity. Cano Island Biological Reserve is one of a number of featured reserves along the coasts. These coasts, such as Drake Bay, are wintering and breeding grounds for humpback whales that come each winter. Ballena National Marine Park is specially designed for this species. Other baleen whales also migrate through the area such as Bryde's whale. Dolphins such as spinner and rough-toothed, and smaller cetaceans such as false killer whales and killer whales are seasonal migrants to these areas. Manatees can be observed occasionally at Manzanillo Beach, Talamanca, and Limon. Creation and threats Because of the remoteness of the peninsula, logging only began in the 1960s. By 1975 there were plans for a major international logging operation. Researchers petitioned President Daniel Oduber to protect the area, which he did by making it a National Park. For this he received the Albert Schweitzer Award from the Animal Welfare Institute. The already present goldminers were allowed to stay. By 1986 their number had increased to about 1,000 (not counting their families), who also hunted wildlife. It was decided to evict them. There is, however, still some illegal mining going on (using more destructive modern mining methods), considered the second invasion, there are about 400 miners currently. It is estimated that 38% of the park (16.000 hectares) have been exploited by