Seed Size and Fruit-Handling Techniques of Avian Frugivores

Abstract

Whether a bird handles a fruit by crushing it with its bill or simply swallowing it whole has important ramifications for both the dispersal success of the plant and the feeding behavior of the bird. In cage experiments, birds that crushed fruits in their bills ("mashers") usually dropped many seeds without ingesting them. Large seeds were dropped more frequently than small seeds. The proportion of seeds dropped by five tanager species correlated negatively with their body weight. Birds that swallowed fruits whole ("gulpers") did not drop seeds before swallowing fruits. Gulpers regurgitated large seeds and defecated small seeds. Median regurgitation time was less than median defecation time. Gulpers had lower ingestion rates than mashers, probably because mashers did not ingest many seeds. Mashers spent more time than gulpers in handling fruits. Mashers may also be less restricted than gulpers of equivalent size in the sizes of fruits they can take. Plants may respond evolutionarily to the differences in the seed-dispersal probability of mashers and gulpers through different fruit presentation methods, shifted fruiting seasons, seed size, and pericarp texture.