With a population exceeding 100 million people, Ethiopia is the second most populous country in Africa. The country features an array of ethnic cultures that cling to ancient traditions associated with Orthodox Christian and Islamic religions, traditional African tribalism, and nomadic pastoralism hosting more than 80 indigenous languages. Ethiopia's topography is as diverse as its people; the Danakil Desert lies 120 meters below sea level while the northern and southern highlands rise to over 4,000 meters. Although widely known for recurring drought and famine, Ethiopia is a vital source of freshwater for many East African countries and is one of the most agriculturally productive countries on the continent. The Ethiopian highlands facilitate orographic rains that provide 90% of the water to the Nile River and support several major watersheds that deliver water to Somalia, Kenya and Sudan. Ethiopia also hosts a diverse compilation of ecosystems, including deserts, semi-arid bushlands, rainforests, savannas, tropical montane forests, heathlands, and the continent's largest expanse of Afro-alpine. As a result, the country is rich with specialized flora and fauna with an exceptionally high incidence of endemism. More than 1,400 plant species are believed to be endemic to Ethiopia representing 10 to 20% of the flora, and, of the 227 mammal species, at least 31 are endemic. There are more than 800 species of birds; at least 16 are endemic.