Status of the northern muriqui (Brachyteles hypoxanthus) in the time of yellow fever

Understanding the impact of zoonotic diseases on wild primate populations is important for assessing local extinction risks and for evaluating potential mitigating factors. Comparative data on demographic changes in two isolated populations of the northern muriqui (Brachyteles hypoxanthus) during a severe yellow fever outbreak in southeastern Brazil provide unique insights into the potential effects of this disease in this Critically Endangered species. From October 2016 to April 2017, the muriqui population at the Reserva Particular do Patrimonio NaturalFeliciano Miguel Abdala (Caratinga) lost 31 of its 324 members, or nearly 10%, whereas the population at the Reserva Particular do Patrimonio NaturalMata do Sossego (Sossego) declined from 34 to 25 individuals, or 26%. Greater per-capita risks to muriquis in the Sossego population could be related to ecological and anthropogenic differences, including a wetter climate and an absence of sympatric howler monkeys (Alouatta guariba), which may have directly or indirectly buffered the Caratinga muriquis. Although we lack definitive confirmation that the muriqui population declines were caused by yellow fever, the timing and magnitude of the losses strongly implicate the disease. We highlight the risks of catastrophic population declines in small populations and emphasize the value of long-term demographic monitoring studies.