 Stanford estimated that the Gombe chimps kill up to 100 colobus monkeys a year, which he believes to be close to a fifth of the colobus population within their territory.Another study confirms that chimpanzees are annually responsible for 6-12 percent of red colobus female and infant death in Ngogo, Kibale National Park, which has one of the largest populations of chimpanzees.It seems that chimpanzees tend to favor the red colobus as prey whenever the two are in the same territory, hunting in groups of up to 20 individual chimps.