All callitrichids include fruit, gums and other plant exu-dates, and insects in their diet. Most species also feed on nectar, other arthropods (e.g., butterflies and spiders), and small vertebrates (e.g., frogs, lizards, bird eggs, and nestlings). Leaves and buds are very rarely consumed. The relative proportion of different dietary components varies considerably between species. Eastern Brazilian marmosets and pygmy marmosets rely heavily on plant exudates that they procure by gouging through the bark of trees and lianas, a behavior facilitated by their short-tusked condition. Amazonian marmosets are also able to gouge, but depend on plant exudates much less than the other marmosets. Given their long-tusked condition, tamarins and lion tamarins cannot gouge and rely on exudate flow stimulated by damage of the bark through
such things as windbreak and wood-boring insects. In contrast to marmosets, their diet is dominated by a high diversity of fruits; saddleback tamarins and moustached tamarins may include up to about 150 different fruit species in their diet. The spectrum of fruits ranges from soft, tiny berries of less than 0.2 in (0.5 cm) in diameter to large, leathery legume pods of more than 12 in (30 cm) in length. Tamarins swallow the seeds of many of the plant species whose fruits they consume and void them with their feces after the adhering pulp has been fully or partially digested. These seeds remain viable after gut passage; tamarins thus contribute to seed dispersal and to the natural regeneration of the forest. Many of the swallowed seeds are large (diameter up to 0.4 in [1 cm], length 0.6-0.8 in [1.5-2 cm]) in relation to tamarin body size, and it has been suggested that this habit possesses a curative function (displacement of gastro-intestinal parasites and stimulation of gut motility).
During seasonal shortages in fruit availability, nectar or gum may become the principal dietary alternative for frugiv-orous species. Goeldi's monkeys exploit fungi as an alternative diet during periods of reduced fruit availability. In contrast, fungi are an important dietary component throughout the year for buffy tufted-ear marmosets. In saddleback tamarins and emperor tamarins nectar may account for 50-75% of all plant food consumed during periods of fruit scarcity.
Strategies for the search and capture of insects and other prey vary between species. Lion tamarins and saddleback tamarins are mainly manipulative foragers. They probe with their hands (which are particularly elongated in lion tamarins) into tree holes and crevices, break up dead bark, turn around leaf litter, and dip into bromeliads to obtain hidden prey. Most other tamarins and the marmosets are "surface gleaners" that obtain camouflaged prey from the surface of leafs and branches; they stealthily approach this prey and then rapidly snatch or grab. For many callitrichids, foraging for prey is the most time-consuming activity, accounting for up to about 45% of the waking hours, and katydids are the top prey for most species. When capturing a katydid, the first bite is directed towards the head; thus they avoid being bitten by the often formidable mandibles.
Differences in prey foraging strategies are an important factor for the sympatric co-existence of different tamarin species and for the formation of mixed-species troops. By searching for and capturing prey at different strata of the forest and with different techniques, saddleback tamarins and moustached tamarins overlap much less in the spectrum of their principal prey items (katydids) in comparison to the plant component of their diet; saddleback tamarins also capture more lizards and other small reptiles, while mustached tamarins feed more often on frogs.
Several marmoset species and saddleback tamarins also forage over swarms of army ants and capture insects and other arthropods that try to escape from the ants.
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