THE DEGREE OF FRUGIVORY OF BIRDS AS ESTIMATED FROM GASTRIC AND FECAL SAMPLES

Abstract

The degree of frugivory (DF) has long been used to characterize the relative importance of fruits to the diet of a bird and, more recently, as a functional trait related to the role of birds in seed dispersal networks. Although quantitative estimations of DF are desirable, general, categorical classifications or coarse estimations of diet composition based in qualitative information are often used. Data on stomach, fecal and regurgitation contents scattered in the literature or easily obtained in the field could be used to provide a quantitative, potentially more reliable assessment of DF. We compiled such data from the literature and our own fieldwork to obtain 12,576 samples for 985 Neotropical bird species, of which 489 species (49.6%) from 61 families had at least one fruit-containing sample. Gastric (i.e. stomach plus regurgitation) and fecal samples provided similar estimates of DF, despite potential differences in the degree of food digestion. The DF we obtained were higher than those presented in the most frequently used source of quantitative DF estimates in the literature (the Elton Traits database). We further explored with a few study cases the utility of stomach, fecal and regurgitation samples to evaluate intraspecific geographic, sexual, and ontogenetic variations in DF, topics rarely investigated so far. We argued that stomach, fecal and regurgitation sample data abundantly available in the literature or obtained from mist-netted birds may be used to produce quantitative assessments of DF likely more reliable than the estimates used so far and useful for a plethora of ecological studies.