New Scientist reports on African primates using natural contraceptives from, of all things, plums:

Like the synthetic progestogens used in the pill, phyto-progestogens have a hormonal contraceptive effect similar to progesterone. Higham’s team found that levels of these progestogens surged in females during the plum season. From August to October, the baboons in the study area feed extensively on the progestogen-rich black plum Vitex doniana. In a group of 13 females, the more progestogen excreted, the less the females’ rumps developed pink sexual swelling – which is what attracts male attention