4 Infant male Alouatta pigra resting on a hammock (photo by Rosalia Pastor-Nieto) 

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... religiosa, Ficus thonningii, Hibiscus, Morus alba, Tecomaria capensis, and Tipuana tipu. Some of these plant species have been successfully fed to primates in North American zoo collections. A more extensive list of nontoxic browse fed to primates in zoos is also provided by Tresz ( 2003 ) ( Table 12.1 , Fig. 12.3 ). In general terms, the total daily amount of food is divided into two or more portions. This is to keep the animals busy by prolonging feeding times and simulating wild conditions. Although each portion may be balanced to meet the nutritional needs of all animals in a group, high-ranking individuals tend to achieve preferential access to high quality foods (Wolfensohn and Honess 2005 ). Hierarchy sometimes deters subordinates from climbing to feeding platforms (pers obs); therefore, it is crucial to verify that low-ranking individuals are also provided with a balanced portion of the diet. Mixed exhibits with two or more species of howler monkeys are not recommended. Size differences, such as those seen between Alouatta pigra and A. palliata may result in intimidation of the smaller A. palliata, forcing them to climb to less optimal feeding stations (pers obs). Captivity provides a very static environment compared to wild habitats, often resulting in reduction in animal attention, propensity to seek, problem solving, and reduced interests in novel items. Environmental poverty , defi ned as “inappropriate social and physical environments in relation to the basic needs of primates” (Hosey et al. 2009 ), may trigger a series of nonadaptive responses, such as increased aggressiveness, abnormal behaviors (such as coprophagy, lethargy, auto-mutilation), stereotypic behaviors, inappropriate sexual behaviors (inappropriate mounts, hyper- sexuality or abnormal postures), inadequate immune response, disease, parasitism, and poor reproductive performance (Meyer-Holtzapfel 1968 ; Harlow and Suomi 1971 ; Mason 1991 ; Sapolsky 1993 ; Boere 2001 ; Hosey et al. 2009 ; Behie et al. 2010 ). Insuffi cient space and isolation are the most important characteristics of an impoverished environment (Hosey et al. 2009 ). Conversely, environmental enrichment consists of a series of measures to modify these impoverished environments, with the goal of improving the physical and social potential of the animals, and therefore improving their quality of life by meeting their ethological needs (Hosey et al. 2009 ). Basic aspects of behavioral enrichment include minimal clinical interventions, minimizing and/or eradicating animal suffering, providing proper nutrition, adequate enclosure design and dimensions, promoting proper social conditions, and shaping novel and interesting environments by creating occupational therapies. Some examples of occupational therapies are food seeking on substrate, foraging plant species within the enclosure, nest-boxes, perches and refuges, promoting three-dimensional locomotion with ropes, tree trunks and/or branches, elevated feeding trays, and group housing (Novak and Suomi 1988 ; Woolverton et al. 1989 ; Boere 2001 ). Moreover, enclosure design is not only linked to psychological well being but also to health. Considering that howler monkeys are tropical primates, housing has to take into account ambient temperature (optimal room temperature should be between 20 and 26 ° C), or an additional heat source should be provided. Another relevant, yet commonly overlooked, enclosure design is the position and location of feeding trays. Howler monkeys are arboreal primates adapted to feed and move on trees, and for this reason it is highly likely that they lack natural immunity to many terrestrial pathogens. Placing feeding trays on elevated platforms can aid in preventing further stress and disease. Enclosures for captive howlers should be designed to meet the needs of arboreal primates. Most zoos that hold howler monkeys include perches, nests, hammocks, and natural foraging vegetation within their facilities. Howler monkeys should be able to move in an elevated, three- dimensional environment (Hosey et al. 2009 ) (Fig. 12.4 ). In captivity, there is a tendency towards inactivity and a lack of use of the prehensile tail. Promoting natural feeding behaviors through enrichment activities, by varying the presentation of the diet encourages activity and use of the tail. Finally, enclosures should be designed with external and indoor sections and a heat source when low temperatures are expected to occur. Aberrant behaviors are sometimes observed, like in Alouatta clamitans as described by Dada ( 2009 ). Among the most common pathologic behaviors are circle locomotion, head and body swinging, back hitting with tail, tongue fl icking to observers, self-mutilation, fl exing and stretching limbs, sexually directed behaviors, and aberrant eating. In this study, singled housed animals showed higher rates of stereotypic behaviors, among which locomotion in circles was observed in highest frequencies, especially before feeding hours, suggesting increased anxiety levels before feeding. Dividing the diet into a number of smaller portions and hiding them in different parts of the enclosure are good strategies to reduce levels of anxiety. Social interactions with familiar conspecifi cs are essential for howler monkeys in captivity (Farmer et al. 2011 ). Other social events such as separation from the mother, a sibling or nursery peer, a cage partner, or a roommate are detrimental for howlers and may result in chronic stress and illness (pers obs). Another factor, possibly associated with captivity stress in some primate species is the visitor effect (Hosey et al. 2009 ), but its responses have not been yet evaluated in howler monkeys in captivity. Conditions associated with overcrowding, lack of behavioral enrichment, and improper enclosure design may lead to otherwise avoidable animal injuries. In many cases, an increase in aggression is observed in overcrowded conditions, when a male sex-biased group is housed together, and when animals are maintained in improper facilities. The most common injuries include lacerations of ears, face, and fi ngers as a consequence of fi ghting. It is worthwhile mentioning that good knowledge of the behavioral characteristics of howler monkeys is essential to prevent injuries caused by fi ghts, aggression, and infanticide (Crockett and Janson 2000 ). Captive howler managers should consider specifi c behavioral traits, such as signs of psychological well being. Factors such as group structure, hierarchy, and age are important factors to take into account to prevent aggressive behavior (Hosey et al. 2009 ). General physical examination in howler monkeys includes dental examination, weighing, blood and stool samples, and rectal swabs for bacteriological cultures. It is also important to evaluate systolic arterial pressure and cardiac frequency, and to check for their coordination (Chagas et al. 2010 ). The pulse can be monitored at the lateral metatarsal area or at the femoral-inguinal region. The recorded clinical parameters are heart rate at 151–194 (bounce/min.), respiratory frequency of 19–25 breaths/min, systolic blood pressure at 154–163 mmHg, and rectal temperature ranging between 37.5 and 39 ° C. Oral and dental examinations are essential to discover oral lesions and dentition problems. The fur and skin of newly acquired howler monkeys should be checked for external parasites, miasis and bacterial infections, especially if suspected to be wild caught. Abdominal palpation is important for checking liver and kidney size, as well as the consistency of intestines and bladder palpation. Flexion and extension of the limbs to check for range of motion and articular fl exibility can be crucial in cases of contracture and arthritis due to captive conditions. Venipuncture for blood samples is in the femoral vein, located in the femoral triangle. The use of a vacutainer is usually recommended to avoid excessive handling of primate blood. Reference hematological values for Alouatta are reported elsewhere (Canales et al. this volume). To perform a thorough medical examination, improved immobilization techniques have made the restraint of monkeys much safer. Before manually restraining a howler monkey, there are several factors to consider, such as the animals’ physical and health condition, temperament, duration of restraint, and the handler’s experience (Ølberg 2007 ). Other important factors involved in successful animal handling are enclosure design and careful planning. It is very important that captive howler monkeys are housed under conditions that allow for safe handling without anesthesia. This may be accomplished by a combination of properly designed facilities and management practices allowing selective movement of animals (Bush 1996 ). The common capture and restraint techniques for howler monkeys are netting and holding the arms and neck while wearing leather gloves. If chemical restraint is used, ketamine hydrochloride is generally a safe drug that has been widely used with excellent results ...