Nomadic Pastoralists raise domesticated relatives of wild undulates such as goats, cattle, camels and sheep. They live almost exclusively off animal product such as milk, meat and blood, though diets are often supplemented with plant products gathered in incidental foraging. The people tend to migrate extensively in search of water and pasture. This system allows humans to occupy areas unsuitable for rain-fed agriculture, although usually at low population densities. The animals are able to convert low quality plant food (grass), which are unusable by humans, into high quality foods such as milk and meat. The population of the animals varies considerably depending on rainfall. The populations are generally higher than those of wild relatives and can therefore feed more people than can otherwise be supported in these environments. Nomadic Pastoralism is usually practiced in savannnas or areas otherwise unsuited for permanant rainfed agriculture. This form of subsistance is therefore most common in Africa, Northern Asia and Arabia. The Massai of Kenya are a well known group of nomadic pastoralists.