Birth-season variation in Japanese macaques, Macaca fuscata.

Japanese macaques, Macaca fuscata, exhibit an annual reproductive cycle that apparently is maintained intrinsically. Translocation of nine troops to new latitudes within the northern hemisphere has had minimal effect on the timing of birth seasonality in these troops; translocation of one troop to the southern hemisphere has resulted in a 6-month forward displacement of birth seasonality in this troop. Limited available evidence indicates that, in the latitudinal zone between Toimisaki (31 degrees 22'N) and Kinkazan (38 degrees 17'N), mean birth date in in-situ troops becomes earlier as latitude of troop localities increases; the same relationship between mean birth date and latitude apparently does not apply to in-situ troops south and north of the Toimisaki-Kinkazan latitudinal zone. Within the Toimisaki-Kinkazan latitudinal zone, earlier mean birth dates at higher latitudes may permit infants to achieve an adequate level of development before the earlier onset of poor winter food conditions. South of the Toimisaki-Kinkazan latitudinal zone, winters are relatively mild and may be less of a factor in infant survival; north of this zone, poor winter food conditions persist so long that earlier infant births may be maladaptive.