Mandrill
Mandrills seem to live in large, stable groups called "hordes". Hordes often number in the hundreds, possibly averaging around 600+ individuals and reaching as many as 845. It is difficult to accurately estimate group size in the forest, but filming a group crossing a gap between two forest patches or crossing a road is a reliable way of estimating group size. The largest group verifiably observed in this way contained over 1,300 individuals, in Lopé National Park, Gabon—the largest aggregation of nonhuman primates ever recorded. These groups are made of adult females and their dependent offspring.