Gabon is a country located on the Atlantic coast of the central part of Africa. It lies on the equator and covers an area of nearly 270,000 square kilometers and has an estimated population of 2.3 million. The country is made up of coastal plains, mountains such as the Cristal Mountains and the Chaillu Massif in the center, and savannah in the east. Libreville is the capital and the largest city of the country. The Coastal Plain is part of the World Wildlife Fund's Atlantic Equatorial Coastal Forest Ecoregion, and has areas of Central African mangroves, including at the mouth of the Muni River on the border with Equatorial Guinea. Its biggest river is the Ogooué, which has a length of 1200 kilometers. In the dolomite and limestone rocks, there are three karst areas with hundreds of caves. In the summer of 2008, a National Geographic expedition visited and documented some of the caves. Tropical rainforests, grasslands, savannahs, large rivers and coastal lagoons cover much of the country, with a wide variety of wildlife. The wildlife of the country includes Forest Elephant, Forest Buffalo, various species of antelopes and monkeys, sitatungas, leopard, golden cat, various jackals, mongooses, genets and civets, three species of crocodile, chimpanzees and gorillas, and several species of sea turtles nesting along the coast. The West African Manatee is common along coastlines and large rivers, and the Humpback Whale breeds offshore. The country is home to 604 bird species, none of which are endemic. There are also many species of snakes, including the Gabon Viper.