A study funded by WWF and conducted by ILRI between 1989 and 2003 monitored hoofed species in the Mara on a monthly basis, and found that losses were as high as 75 percent for giraffes, 80 percent for common warthogs, 76 percent for hartebeest, and 67 percent for impala. The study blames the loss of animals on increased human settlement in and around the reserve. The higher human population density leads to an increased number of livestock grazing in the park and an increase in poaching. The article claims, "The study provides the most detailed evidence to date on the declines in the ungulate (hoofed animals) populations in the Mara and how this phenomenon is linked to the rapid expansion of human populations near the boundaries of the reserve."
In the Serengeti National Park, a proposed 50-kilometre (31 mi) road from Musoma to Arusha, with tarmac touching the Serengeti, is raising criticism from scientists who say that the road will disrupt the annual migration of the wildebeest, and that this disruption would affect predators such as lions, cheetahs and African wild dogs, as well as the grasslands themselves.According to CCTV "The route is expected to carry 800 vehicles a day, mostly trucks, by 2015 and 3000 vehicles a day an average of one every 30 seconds by 2035, a campaign promise made by Tanzanian President Jackaya Kikwete [sic] in 2005". In late June 2011 the Tanzanian government decided to cancel the Serengeti road plan due to global outcry.