How Important Are Arthropods In the Diet of Fruit-Eating Birds?

ABSTRACT In most dietary studies of fruit-eating birds, sampling methods consist of direct observations of foraging and fecal sample analyses, and the consumption of resource types is measured as the percent of occurrence in diet samples, or as counts (frequency) of ingesteditems. Since these measures are usually biased towards the overestimation of small and abundant resources, the amount of ingestedmass is a more accurate measure of the crude energy and nutrients provided by a given food source. In this study, we use direct observations of foraging behavior to describe the diet of four frugivorous- insectivorousbird species during the breeding season in Southern Yungas forests, and we compare the number of ingesteditems and ingesteddry mass as measures of fruit and arthropod consumption. In terms of ingested fooddry mass, fruit consumption represented over 95% of the diet of the four bird species. The estimated proportion of fruit in the diet differed significantly among methods in three bird speci...