Stomachs Of Species Research Articles

IS THE INGESTION OF SMALL STONES BY DOUBLE-CRESTED CORMORANTS A SELF-MEDICATION BEHAVIOR?

Abstract Many birds ingest small stones to aid in the grinding up of coarse food items in the diet. However, small stones are also found in the stomachs of species with diets consisting of soft food items, and may serve to mechanically remove parasites attached to the stomach wall. We sampled Double-crested Cormorants (Phalacrocorax auritus) at two sites to examine whether ingestion of small stones served an antiparasite function and whether this behavior differed between the sexes. At a Lake Ontario site, females more often had small stones in their stomachs and were less parasitized by nematodes than were males, and males with small stones had fewer nematodes than males without small stones. We did not find similar patterns in small stone presence or parasitism at a Lake Erie site; however, Lake Erie birds had fewer parasites and lower proportions of birds with small stones. These results suggest that ingestion of small stones by Double-crested Cormorants might indeed serve an antiparasite function.

The Diets of Neotropical Trogons, Motmots, Barbets and Toucans

Although membership in broad diet categories is a standard feature of community analyses of Neotropical birds, the bases for assignments to diet categories are usually not stated, or they are derived from anecdotal information or bill shape. We used notations of stomach contents on museum specimen labels to assess membership in broad diet categories (“fruit only,” “ arthropods only,” and “fruit and arthropods”) for species of four families of birds in the Neotropics usually considered to have a mixed diet of fruit and animal matter: trogons (Trogonidae), motmots (Momotidae), New World barbets (Capitonidae), and toucans (Ramphastidae). An assessment of the accuracy of label data by direct comparison to independent microscopic analysis of actual stomach contents of the same specimens showed that label notations were remarkably accurate. The specimen label data for 246 individuals of 17 species of Trogonidae showed that quetzals (Pharomachrus) differ significantly from other trogons (Trogon) in being more fiugivorous. Significant differences in degree of frugivory were found among various Trogon species. Within the Trogonidae, degree of frugivory is strongly correlated with body size, the larger species being more frugivorous. The more frugivorous quetzals (Pharomachrus) have relatively flatter bills than other trogons, in accordance with predictions concerning morphology of frugivores; otherwise, bill morphology correlated poorly with degree of fiugivory. An analysis of label data from 124 individuals of six species of motmots showed that one species (Electron platyrhynchum) is highly insectivorous, differing significantly from two others that are more frugivorous (Baryphthengus martii and Momotus momota). An analysis of 135 individuals of 12 species of barbets showed that although “fruit only” predominated among almost all species, arthropods are more frequently recorded in the stomachs of species in the genera Eubucco and Capito than in Semnornis. The highly frugivorous diet of Semnornis species is yet another parameter in which they resemble toucans more than New World barbets. Data from 326 individuals of 32 species of toucans showed that the family is remarkably homogeneous in the predominance of fruit in the stomachs of all species. These data suggest hat the degree to which toucans prey upon bird eggs and nestlings, and animal matter in general, is overemphasized. Although our data suggest that it is safe to assign toucans to a “fruit only” category in community analyses, such assignments must be taken on a genus-by-genus or species-byspecies basis in trogons, motmots, and barbets.