Role of vocalisations and social housing in breeding in captive howler monkeys (Alouatta caraya)

Over the last 12 years the European captive population of black and gold howler monkeys, Alouatta caraya, has increased at a slow rate and many groups have not produced offspring. This study aims to determine the influence of social organisation of captive groups and both performing and hearing howl vocalisations on reproductive success. Data were extracted from the European Studbook to calculate three variables of female reproductive success per capita, for each year of their reproductively active life (from three years of age). Reproductive success for females was measured as the occurrence of a birth each year, the total number of births per year and the number of successful births per year (offspring surviving to one year of age). Male data were analysed separately, using behavioural observations in addition to studbook data, to determine the effect of daily howling rates on reproductive success (mean number of offspring surviving to one year of age). We found that more offspring were born to and survived (both P < 0.001) from females held in family groups than those in pairs. Male howler monkeys held in family groups had a higher mean number of offspring born per individual than those held in a pair (P < 0.001) and males which performed a higher howl rate also had increased reproductive success. We also found that for females, regularly hearing the howls of familiar conspecifics was related to an increase in reproductive success (P = 0.003). This study provides the first evidence of a link between howling and reproductive success in A. caraya and provides suggestions for the management of captive black howlers to increase the current captive population.