Feeding ecology and diet

All species show clear preferences for ripe fruit when it is available, and supplement their diets with various quantities of leaves. Woolly monkeys at La Macarena, Colombia also consume substantial quantities of insects. Other foods, such as flowers and nectar, and new shoots are eaten when available, while bark and bamboo supplement diets during periods of preferred food scarcity.

Howler monkeys are by far the most folivorous, but the proportion of leaves in their diets varies greatly by habitat. Sym-patric species exhibit considerable overlap in diet, feeding on many of the same fruit, leaf, and flower species, sometimes from the same trees or lianas. There are interesting parallels in the proportion of fruits versus leaves in the annual diets of sym-patric spider monkeys and howler monkeys, on the one hand, and those of sympatric muriquis and howler monkeys, on the other hand. In each pair, the howler monkeys are substantially more folivorous than either spider monkeys or muriquis.

There is also extensive intraspecific variation in diets. For example, populations of southern muriquis inhabiting dis-

turbed or regenerating forest fragments devote up to 70% of their feeding time to leaves, whereas those inhabiting undisturbed, continuous forest devote up to 70% of their feeding time to fruits. The latter also utilize much larger home ranges, and occur at much lower population densities. Whether low population density permits them to maintain a more frugiv-orous diet by expanding their home range, or whether undisturbed forests have more abundant fruit is not yet known.

All genera possess prehensile tails, which permit them to feed for long periods of time in suspended postures. Secured by their tails, they can access foods close to the ground or from plants and branches that are too small or flimsy to support their body weights. Their tails also free up their hands, which they can use to sort foods and bring them to their mouths. The atelins also travel by suspensory locomotion, using their arms and tails to swing through the canopy. Suspensory locomotion permits them to travel long distances rapidly, and may contribute to their ability to monitor dispersed patches of preferred fruits. Howler monkeys are quadrupedal, traveling much shorter distances more slowly than the atelins.

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