Sexual Dimorphism and Foraging Behavior of Emerald Toucanets Aulacorhynchus prasinus in Costa Rica

Abstract

Foraging behavior and diet of male and female Emerald Toucanets were studied at Monteverde, Costa Rica during both wet and dry seasons to determine if sexual dimorphism in bill morphology was related to differences in feeding behaviors between sexes. Based on analysis of museum specimens, bills of males averaged about 20% longer than those of females and the sexes could be reliably distinguished based on differences in bill morphology. Analysis of foraging sequences as first-order Markov chains revealed no differences between sexes or seasons in relative height, relative position in a plant, or foraging substrate. Regardless of season, both male and female toucanets foraged on twigs in outer portions of the mid-canopy. Seasonal differences existed in foraging height above ground, time spent in a single foraging bout, and distance moved between foraging bouts. However, the only within-season difference between sexes was that an average foraging bout during the dry season was longer for females than for males. Toucanets were observed eating fruits, mostly berries, and flowers from 47 species of plants. Fruits consumed in the wet season were larger and heavier than those consumed in the dry season, but no obvious within-season differences existed between sexes in size, color, or type of fruit consumed. We conclude that sexual dimorphism in bill morphology of Emerald Toucanets is not related to differences in foraging behavior or diet. Because of the nature of the resource, foraging-related sexual dimorphism should be rare in frugivorous birds.