The diet of nestling and breeding White-tipped Plantcutters (Phytotoma rutila)

Abstract

ABSTRACTThe plantcutters (Phytotoma), a group of three endemic Cotingidae from southern South America, are the most folivorous passerines yet known. Although the foods of adult plantcutters have been investigated, there is no information on the diet of their nestlings, nor on the foods collected by breeding adults. This aspect is of interest because it is proposed that levels of digestible protein in leaves may limit rapid growth of altricial nestlings; and in fact, so far, no small land bird is known to be raised on such a diet. We investigated the diet of White-tipped Plantcutter (P. rutila) nestlings near Córdoba, Argentina, by analysis of the excreta collected from two nests, and recorded the foraging of breeding adults during 5 weeks. The diet of nestlings was mainly leaves, supplemented with fruits; no animal matter was fed by parents. Yet they do not grow slowly. Likewise, breeding adults did not collect insects or other arthropods. This is the first passerine yet known to raise nestlings on a diet of mainly leaves supplemented by fruit, confirming the uniqueness of plantcutters.