Mantled Howler Monkey (Alouatta palliata) Demographic Structure in a Continuous Forest Compared to a Small Forest Fragment in Costa Rica.

In the face of widespread habitat destruction and forest fragmentation, it is critical to understand primate demography to assess population viability across populations inhabiting continuous forests and fragmented landscapes. While mantled howler monkeys (Alouatta palliata) have traditionally been considered resilient to habitat destruction, their populations are declining and are now rated “Vulnerable” on the IUCN Red List of Threatened Species. In this study, we assessed the demography of the mantled howler monkey population at La Selva Research Station, a protected forest in northeastern Costa Rica— providing the first systematic study of population structure in 30 years. In 2022, we conducted a howler census to ascertain the number of groups at La Selva and recorded group size and composition for a subset of the groups. We then compared population density, group size and composition with a population in a nearby protected forest (La Suerte Biological Research Station, LSBRS) to help assess the viability of mantled howlers in a small forest fragment. The mantled howler population at La Selva has grown substantially since 1992 with, at the time of the survey, 25 groups and a population density of 23.4 individuals/km². Mean group size was 14.3 with a sex ratio of 1:2.2 and immature to adult ratio of 0.7—in line with mantled howler monkey populations throughout the species’ range. The population density at La Selva was, however, almost five times lower than the forest fragment at LSBRS, although group size and composition did not differ across sites. Overall, our results highlight the importance of forest protection for mantled howler monkeys. [ABSTRACT FROM AUTHOR]