Introduction Like most other howler monkeys, brown howlers (Alouatta guariba) form one-male groups with up to 10 individuals. Even if there is more than one adult male, the alpha male howler monkey usually monopolizes all reproductive females and sires all young (Pope, 1990). However, extragroup copulations (EGCs) have been observed in Alouatta pigra (Horwich, 1983) and A. seniculus (Agoramoorthy and Hsu, 2000). Here we report the first EGCs observed in A. guariba clamitans |