Annual birth patterns of savanna baboons (Papio cynocephalus anubis) over a ten-year period at Gilgil, Kenya.

Most cercopithecines reproduce on a seasonal basis, but the proximate mechanisms influencing birth periodicity are often unclear. We analyze 10 years of data from the Gilgil Baboon Project (Kenya) in order to examine the relationship between annual birth patterns and rainfall. Savanna baboons at Gilgil copulated in all months of the year, and births did not occur on a seasonal basis. Annual rainfall patterns showed no association with annual birth patterns, but the chances of conception were significantly greater following the end of the long rainy season than at other times of the year. Nonseasonal reproduction is a general characteristic of savanna baboons (Papio cynocephalus subsp.) throughout Africa. The extreme dietary diversity of baboons enables them to utilize a wide variety of resources and facultatively manipulate the timing of different stages in the reproductive cycle in accordance with resource availability. We predict that nonseasonality of reproduction will be more likely to occur among species with a large dietary diversity than among species with a more restricted diet.