The migratory - and some resident - wildebeest, which number over 1.5 million individuals, constitute the largest population of big mammals that still roam the planet. They are joined in their journey through the Serengeti-Mara ecosystem by 200,000 plains zebra, 300,000 Thomson's gazelle and Grant's gazelle, and tens of thousands of topi and Coke's hartebeest. Masai giraffe, waterbuck, greater kudu, impala, common warthog and hippopotamus are also abundant. Some rarely seen species of antelope are also present in Serengeti National Park, such as common eland, klipspringer, oribi, reedbuck, roan antelope, sable antelope, steenbok, common duiker, bushbuck, lesser kudu, fringe-eared oryx and dik dik. Herds support 7,500 hyenas, 3,000 lions, and 250 cheetahs. There are more than 500 birds and 300 mammal species.