Previous studies on births in nonhuman primates suggest that births are expected to occur at night to avoid predators. Here, we describe birth-related behaviors in wild black and gold howler monkeys, Alouatta caraya and address the various ideas proposed in the literature about the timing of births in group-living nonhuman primates. We collected data on females' birth-related behaviors through continuous focal observations and scan samples. Focal observations on females giving birth were taken for the remainder of the day after noticing a female was in labor. We recorded behaviors and the spatial distribution of the whole group using scan samples taken every 10 min from sunrise to sunset the same day of birth. We recorded five births at the continuous forest (CF) over a 25 months period (January 2004-December 2004 and September 2005-September 2006) and two births in the fragmented forest (FF) over a 13 months period (September 2005-September 2006). From these, four births were during daylight (two at CF and two at FF) and three during the night at CF. Our descriptions of A. caraya births contribute to a growing data set on the timing of parturition in wild nonhuman primates and suggest that a clear pattern of nocturnal births is not universal across nonhuman primate species.

Ecological and social factors have a significant effect on infant survivorship in nonhuman primates. We present 6293 group-months of infant birth and mortality data for 29 groups of Alouatta caraya inhabiting a flooded forest in northeastern Argentina, collected over 1.5-8 yr depending on the group. We tested whether infant mortality was a response to the effects of flooding on food availability and whether male takeovers resulted in greater opportunities for infanticide. During our study, 43 of 113 infants died at a mean age of 5 mo. In 24 cases the cause of death was unknown. In the remaining 19 cases infant deaths were attributed to periods of intense flooding (N08), replacement of the breeding male (N08), problems associated with birth (N02), and injuries during an intergroup encounter (N01). Flooding reduced the availability of mature leaves, which appeared to play an important role in the ability of mothers to nurse their offspring. Male replacements occurred in four social groups that contained only one fully adult male. Infant mortality was significantly higher in groups that experienced male replacement compared to groups without male replacement. These results indicate that infant mortality in Alouatta caraya is affected by several factors-natural disasters, maternal condition and food availability, infanticide after male replacement, and possibly disease and predationeach of which needs to be evaluated to understand the history and demography of this primate population.

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In this study, we examined the influence of demography and social context on mother-offspring conflict in wild black and gold howler monkeys (Alouatta caraya) inhabiting two nearby sites in northern Argentina, one comprising continuous forest and one fragmented forest. These sites differed in population density (3.25 vs. 1.04 individuals/ha), degree of home range overlap between neighboring groups (70 vs. 31%), and rate of intergroup encounters (2 vs. 0.02-1 encounters/day), though not in interbirth interval or rate of infant mortality. During a 27-month study (September 2008 through November 2010), we observed 37 mother-offspring dyads across the two sites. We found a very similar pattern of mother-offspring conflict in both populations; specifically, the sites did not differ in any of the variables used to characterize the mother-offspring relationship (the time spent in contact, the rate at which the mother makes and breaks contact, the rate at which the infant breaks contact, the rate of maternal rejection, and signs of infant distress) except one (the rate at which the infant makes contact). Although mother-offspring conflict is a dynamic process that varies over time, our results suggest that the different demographic and social contexts found at the two study sites did not have a marked effect on quantitative aspects of the mother-offspring relationship in these populations of black and gold howlers. Finally, this study suggests that the environmental variability (ecological, demographic, and social traits) leads to a set of strategies used both by infants and mothers with a main goal of conflict resolution, with mothers specifically aiming to cope with the tradeoff between current and future reproduction.