Howler monkeys living under the highly degraded conditions at Balancán, Tabasco, could be showing adaptability by modifying their physiology, hematology, and blood chemistry in response to the conditions of their fragmented landscape.

Allo-grooming is perhaps the most powerful affiliative behavior observed in nonhuman primates. However, the functional significance of grooming in New World monkeys has not yet been fully understood, perhaps because grooming is less frequently observed in platyrrhines. To differentiate the potential role of affiliative investment and/or kinship on sharing access to food (co-feeding) in spider monkeys, behavioral data on grooming, embracing, and feeding were collected from two different groups of captive study subjects: a familiar/kin group and a nonfamiliar/non-kin group. The results of this study suggest that family-related spider monkeys that engage in grooming tend to share access to food resources more than unfamiliar conspecifics that do not groom. One explanation for this difference is that the unfamiliar study subjects had not yet invested in the affiliative social network, were not reciprocating their affiliative investments and hence, had a higher tendency toward single animal monopolizing resources. Degree of relatedness alone was not found to be a determinant for sharing the access to food, suggesting that familiarity in spider monkeys is based on the extent to which animals invest in affiliative relationships. In this study, only animals that had engaged in long-term grooming and recognized each other as familiar shared the access to food. Therefore, it might be likely that in spider monkeys, longterm grooming of high intensity has to be developed for co-feeding to occur.

Among platyrrhines, howler monkeys are commonly traded illegally as pets in Central and South America, resulting in the high mortality of specimens. Many of these animals end up in long-term captive situations in zoos and rehabilitation centers, where adaptation may be diffi cult. Careful husbandry planning, taking into account the animals' behavioral, anatomical, and evolutionary characteristics, can greatly improve survivability. This chapter aims to provide information on howler monkey welfare in captivity, including enclosure design, environmental enrichment, feeding and nutrition, and diseases, based upon the biology and ecology of the species. Digestive physiology, behavioral ecology, and the social system of howler monkeys are major factors to take into account to provide adequate captive conditions. Aspects such as social integration, controlled temperature, indoor and outdoor enclosures, and hiding places should be met. The provision of foraging plants within the enclosure is ideal to stimulate natural feeding behavior. Behavioral enrichment measures need to be devised to prevent behavioral disorders. For successfully maintaining howler monkeys in captivity, animals should be trained to consume a wide variety of natural fi ber sources. Special attention should be placed on quantities of food sources rich in gluten and other allergenic proteins. Acute and chronic syndromes such as gastric dilatation, howler monkey wasting disease, and metabolic bone disease can be prevented when provided adequate diets. Many diseases may be acquired in the wild. However, other infectious diseases (viral, bacterial, and parasitic) are concomitant to stress and improper management. Very few studies have been carried out in captive howler populations to fully understand the husbandry and care requirements. Although howlers are very adaptive in nature and although it is a genus widely distributed throughout Central and South America, they are susceptible to many diseases that might threaten their population in the wild. Achieving a better knowledge of these factors in captivity may contribute to the development of healthy captive populations for future reintroductions to the wild.