AbstractAdult male redtail guenons (Cercopithecus ascanius) live as resident males in heterosexual groups or as nonresident males outside groups. Data are reported here on movement and temporary intrusions by nonresident males in heterosexual groups. These data further elucidate the reproductive strategies of this class of individual. Observations of three radiocollared males provided data on the details of their movement relative to groups. Regular sampling of three heterosexual groups provided data on patterns of nonresident males' intrusions. During peak mating months, nonresident males formed loose affiliations with groups. The males affiliated with one group at a time, with each affiliation lasting several weeks. Nonresident male intrusions in groups were unevenly distributed and were not correlated with the number of potentially fertile females in each group. Estimates of male density indicate that there were about two nonresident males per group, which suggests an adult sex ratio of three females per male within the study area. Nonresident male redtail guenons apparently do not spread their reproductive efforts over several groups at once, but instead each male tends to direct his attention toward the group offering the best opportunity for reproductive payoffs. Factors that determine which groups they attempt to infiltrate may include the characteristics of resident males, female choice, or both, but the number of fertile females probably has no effect. The male low density and female‐biased sex ratio among adults should facilitate resident males' attempts to monopolize fertilizations in groups; however, resident males were unable to prevent copulations by nonresident males even when only one nonresident was intruding in a grou
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