Howler Monkeys by Martín M. Kowalewski Paul A. Garber Liliana Cortés-Ortiz Bernardo Urbani & Dionisios Youlatos

Author:Martín M. Kowalewski, Paul A. Garber, Liliana Cortés-Ortiz, Bernardo Urbani & Dionisios Youlatos
Language: eng
Format: epub
Publisher: Springer New York, New York, NY

8.6 Summary

Compared to other arboreal quadrupeds, which regularly integrate distinct locomotor modes into a single bout of travel, Alouatta locomotion is dominated by slow quadrupedal progression along relatively large horizontal supports. Despite the remarkable variability in postural behavior that the prehensile tail affords, their locomotor profile is quite restricted or conservative in contrast to many other primate genera and this lack of locomotor variability is particularly notable when contrasting Alouatta to other ateline genera (Guillot 2009; Youlatos and Gasc 2011). Although Alouatta diverged relatively early in ateline evolution, it is increasingly clear that they are a poor model of the ancestral state. Their overall positional behavior involves a suite of derived behavioral and morphological adaptations unique to this genus (Erikson 1963; Cant 1986; Schön Ybarra and Schön 1987; Rosenberger and Strier 1989; Kagaya 2007; Youlatos and Gasc 2011; Youlatos and Meldrum 2011).

Despite the dominance of slow quadrupedalism behaviors among all howler species, this review reveals subtle interspecific distinctions. The earliest derived groups, occupying the northernmost and southernmost extent of the howler geographic distribution, exhibit increased reliance on quadrupedalism. In contrast, more recently derived species, such as A. seniculus, exhibit higher frequencies of climbing, clambering, and bridging. Further evaluation of these patterns will benefit from additional studies, particularly of less well-known species including A. pigra, A. arctoidea, and A. guariba. In addition, it will be valuable to further explore the relationship between habitat differences and positional behavioral differences seen among species of Alouatta.

In terms of habitat use, howlers demonstrate a relative consistency. Almost all species use the high forest layers, the central tree zones during traveling and the tree peripheries during feeding. Lower forest layer or ground use is occasional and frequently related to the exploitation of particular food sources. This pattern of forest utilization is consistent with predictions related to body mass and feeding niche segregation among platyrrhines, where large bodied herbivores occupy and negotiate with no particular difficulty the higher and peripheral parts of tree crowns (Fleagle and Mittermeier 1980; Rosenberger 1992). This pattern is also related to substrate use, where howler species, especially the seniculus group, exhibit high rates of small branch utilization. This is further associated with the more flexible positional habits that allow them to use multiple and variable paths to travel between feeding sites and exploit them more efficiently. On the other hand, the use of larger substrates and inner parts of trees provide secure pathways whereupon howlers guide themselves safely in order to gain access to more unstable parts of crowns. However, associations between positional modes, used substrates, and tree crown parts have not yet been explored in detail. Further research in relation to travel patterns and spatial mapping would provide valuable information in order to understand any interrelations between cognition and morphology for an integrated understanding of their adaptive significance.

Apart from that, more studies are required in order to establish or clarify any interspecific similarities and differences, as reviewed in this chapter. First of all, we need additional data on the positional profiles

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