The impact of alpha male replacements on reproductive seasonality and synchrony in white-faced capuchins (Cebus imitator)

Objectives Reproductive seasonality is typically associated with ecological factors, but it can also be related to social factors, such as alpha male replacements (AMR). Such events can produce distinct birth peaks outside of the ecological peak, potentially increasing hardship for mother and infant and ultimately reducing fitness. We examined the impact of AMRs on birth seasonality, birth synchrony, and infant survival in the Santa Rosa population of white-faced capuchins (Cebus imitator). Materials and Methods We analyzed 33 years of data on seven capuchin groups to test whether AMRs and births occur seasonally and whether birth seasonality changes following AMRs. Using sliding window analysis, we tested whether ecological conditions predict births in future months. We also tested whether birth period affects infant survival and likelihood of infanticide. Results AMRs shift birth seasonality from the ecological birth peak in the early wet season (late May-July) to a social birth peak during the late dry season (March-May), but they do not affect synchrony. In addition, we found that being born in the social peak significantly decreases infant survival relative to individuals born in the ecological and nonpeak periods. Discussion These findings suggest that Santa Rosa's predictable seasons can provide conception cues for female capuchins, but AMRs disrupt this ecological timing of conceptions. We suggest the increased infant mortality associated with the social birth peak is related to seasonal factors, including water scarcity and varying resource availability, and increased risk of infanticide, as the social birth peak overlaps with the AMR peak.