Parasitic infections of three Mexican howler monkey groups (Alouatta palliata mexicana) living in forest fragments in Mexico.

In order to better understand how patterns of parasitism in howler monkeys are affected by forest fragmentation, we carried out a 1 year survey of gastrointestinal parasites in fecal samples from three groups of Mexican howler monkeys inhabiting different forest fragments in the Los Tuxtlas Biosphere Reserve, Mexico. The study groups were chosen because the conditions in which they lived suggested a potentially negative gradient for parasite richness and a positive gradient for levels of parasitism. We report for the first time the presence of Entamoeba coli in Alouatta palliata mexicana and of hookworms (Family Ancylostomidae) in A. palliata. A reduction in home range size and an increase in disturbance was associated with a loss of parasite richness, which in general was high. Parasite prevalence and the proportion of contaminated samples in which each parasite taxon was present was also high in general and there were no differences between groups. A factor related to the generally high levels of parasitism in our study groups could be the high humidity in the study area, because this favors the survival of parasitic free forms and increases the chances of infection. This would also account for the tendency towards higher levels of parasitism observed in the rainy season. Finally we did not find a pattern relating sex and parasitism.

Coalitions and male-male behavior in Alouatta palliata.

Coalitions influence the establishment and maintenance of social relationships among males in primate species. In this study, we compare the social behavior of males between two groups of Alouatta palliata: a group that was recently taken over by a coalition of two males (Mt), and a group that had a stable composition for at least 9 months (Rh). We predicted that coalition partners would be more cooperative and less competitive than dyads formed by immigrant and long-term resident males, and dyads formed by long-term resident males. Additionally, we predicted that these dyadic trends should be reflected in more competition and less cooperation in the group that was taken over. As predicted, the coalition partners of Mt showed the highest levels of cooperation among all dyads and the second lowest rate of agonism. Cooperation was higher in the group that had a stable composition. Results from this study suggest that the social relationships of male mantled howlers vary as a function of familiarity between males and that in the context of coalitionary takeovers, coalitionary males are highly cooperative. Cooperation is lower in groups recently taken over and competition is more intense, perhaps as a consequence of the process of establishment and reorganization of power relationships within some dyads. In the future, we must determine the frequency of coalitionary takeovers in this population and assess its ultimate consequences for male-male social relationships.

Differences in diet and activity pattern between two groups of Alouatta palliata associated with the availability of big trees and fruit of top food taxa.

The threat that forest fragmentation and habitat loss presents for several Alouatta taxa requires us to determine the key elements that may promote the persistence of howler monkeys in forest fragments and to evaluate how changes in the availability of these elements may affect their future conservation prospects. In this study we analyzed the relationship between the availability of both big trees of top food taxa (BTTFT) (diameter at breast height>60) and fruit of top food taxa (FrTFT) in the home ranges of two groups of Alouatta palliata mexicana occupying different forest fragments in Los Tuxtlas, Mexico, and their diet and activity pattern. Both study groups preferred big trees for feeding and the group with lower availability of BTTFT in their home range fed from more, smaller food sources. Furthermore, both study groups also increased the number of food sources when their consumption of fruit decreased, and the group with lower availability of FrTFT in their home range fed from more food sources. The increase in the number of food sources used under such conditions, in turn, set up a process of higher foraging effort and lower rest. In summary, our results support other studies that suggest that the availability of big trees and fruit may be two important elements influencing the persistence of howler monkeys in forest fragments.

Foraging habits of Alouatta palliata mexicana in three forest fragments.

The activity patterns and diet of howler monkeys (Alouatta palliata mexicana) were studied in 3 forest fragments in south-eastern Mexico: Playa Escondida (PLA), Agaltepec Island (AGA) and Arroyo Liza (LIZ). Intersite differences offered the opportunity to investigate the foraging adaptations of howler monkeys in response to population and habitat size. In the largest fragment (PLA), the howlers' diet was based on high-quality items (fruit and young leaves). In AGA, where the density of howlers was the highest, their diet was mostly folivorous with a marked exploitation of uncommon food items such as vines, lianas, shrubs and herbs. The dietary differences in AGA were accompanied by more time spent travelling and less time spent resting. Although LIZ was the smallest fragment and had a high howler density, the small group size and the use of energy-minimizing strategies (less time spent travelling and more time spent resting) probably allowed howlers to maintain a frugivorous diet.

Glucocorticoid levels in free ranging resident mantled howlers: a study of coping strategies.

A growing amount of data shows that a preference for passive-nonaggressive over active-aggressive problem solving is associated with higher levels of glucocorticoids (GC). For mantled howlers, the arrival of an adult male in a new group is a potential source of psychological stress for both resident males and females. Resident mantled howler males take an active stand and aggressively repel the entrance of solitary males, while females take a passive-nonaggressive stand. In order to study whether the relationship between coping strategies and the activation of the hypothalamic-pituitary-adrenal (HPA) axis observed in other species applies to the response of resident mantled howlers to the presence of solitary males, we examine the relationship between different group and subpopulation variables and the GC levels measured in feces collected from 10 groups living in six forest fragments, in Los Tuxtlas, Mexico. The results of our study suggest that the resident mantled howler females' passive response to the presence of solitary males is accompanied by the activation of the HPA axis, whereas resident males' aggressive response is not accompanied by any changes in the HPA axis. In contrast, a previous study suggests that resident male howlers respond by increasing their testosterone levels to the presence of solitary males (Cristobal-Azkarate et al., Hormones and Behavior 2006;49 261-267). These different behavioral and hormonal responses coincide with the active and passive coping styles described for other species. The conditions in which howlers live in our study area may be favoring the interaction between solitary and resident howlers, and inducing chronically high GC levels, which in turn could negatively affect the fitness of these subpopulations.

Biogeographical and floristic predictors of the presence and abundance of mantled howlers (Alouatta palliata mexicana) in rainforest fragments at Los Tuxtlas, Mexico.

This research focuses on identifying the principal habitat characteristics that influence the presence and abundance of mantled howlers in forest fragments. We provide information on the demography of several fragmented Alouatta palliata mexicana subpopulations at Los Tuxtlas, Mexico, and relate this to the biogeographical and floristic characteristics of the forest fragments inhabited. The most important habitat characteristics related to the presence and abundance of howlers in the fragments were fragment size and floristic diversity. On the other hand, some evidence suggests that given the conditions under which howlers in our study area live (i.e., small and degraded fragments with high densities), secondary vegetation may be beneficial for the survival of the howlers. Finally, we discuss the possibility that the very low immature-to-female ratio (IFR) in the groups, and the lack of juveniles found in many of the study groups may be due to high mortality rates in immatures. A reduction in food availability because of the high population densities of these groups may be responsible for this process.

Allogrooming behavior inCercocebus torquatus: The case for the hygienic functional hypothesis.

The hygienic functional hypothesis of allogrooming behavior was examined in two captive groups (N=9 andN=8) of white-crowned mangabeys (Cercocebus torquatus lunulatus) by analyzing: (1) the corporal distribution of manipulation type according to hair density, and (2) the corporal distribution of allogrooming according to presence of wounds. In both groups the sites with higher hair density received more bouts of Superficial Grooming, which implies a tactile screening of a fragment of the body surface. Only one group tended to emit more allogrooming on the body sites when they were wounded. In the other group, however, the number of wounds was very small and the wounds concentrated predominantly on those sites which were accessible to the subject itself. Thus, our results may be consistent with the hygienic functional hypothesis of allogrooming behavior in general and with the sanitary one in particular.