Factors Influencing the Reproductive Success of Female Black Howlers (Alouatta pigra)

Measuring reproductive success is necessary to determine an organism's fitness, and thus, to address evolutionary processes. In this study we determined the effects of social, ecological, and individual attributes on the reproductive success of black howlers ( Alouatta pigra ) measured through infant survival and interbirth intervals (IBIs). From 2006 to 2012 we studied 29 black howler ( A. pigra ) females living in 11 groups in Campeche (Mexico), and recorded 82 births. We recorded group size and composition and the sex of infants during weekly surveys. We calculated a food availability index based on rainfall levels and on the size of preferred food resources. Daughters had a 30 % higher probability of surviving than sons, and the survival of the latter was positively related to food availability. IBI decreased when the first infant in the interval died, and when considering only IBIs in which the first infant survived, IBIs were longer following the birth of a daughter. These results suggest that, even if the production of daughters reduces reproductive output due to longer IBIs, female black howlers may still accrue higher reproductive success through their daughters due to differences between sexes in survival.