A 12-year study of redtail monkeys in Uganda by Tom Struhsaker showed great variation in diet between months, years and neighboring groups with overlapping home ranges. These rain forest monkeys feed mainly on fruit and insects, but also flowers, buds and leaves. Sometimes they ate more fruit, while at other times more insects. The variation within this population shows how important it is to understand variation within a species before making comparisons between species. Furthermore, hybrid monkeys living in redtail social groups ate more insects than either of the parental species, supporting the idea that diet is affected by genetics.