Flower Eating by Emerald Toucanets in Costa Rica

Abstract

Although many tropical birds visit flowers while foraging (e.g., Snow and Snow 1971), few instances of birds consuming flower parts other than nectar or pollen have been reported. Skutch (1944) mentions observations of a Prongbilled Barbet (Dicrorhynchusfrantzii) and saltators eating flowers. Parrots also apparently eat flowers in some tropical areas (Feinsinger et al. 1979, Janson et al. 1981). Here we report three observations of flower eating made at Monteverde, Costa Rica (1018'N, 84048'W) during a study of the foraging behavior of Emerald Toucanets (Aulacorhynchus prasinus), an abundant frugivorous bird of the tropical lower montane forest. (1) Erythrina lanceolata (Leguminosae). During dry season in midmorning on 7 January 1985, we observed a male and female Emerald Toucanet (distinguished by bill size and shape [Riley 1986]) land in an Erythrina tree, a common legume found in montane regions of Honduras, Nicaragua, Costa Rica, and Panama (e.g., Krukoff and Barneby 1974). Both birds immediately began eating the red flowers, sitting in one spot and reaching to grab flowers from nearby branches. We focused our attention on the male, who ate 13 flowers in 2.3 minutes from his initial perch. He moved 1 m and consumed 15 more flowers in the next 7.6 minutes. While feeding, he became noticeably larger. The female ate fewer flowers and stopped foraging after about 6 min. The birds left together after about 10 min in the tree. Close inspection of the tree in which the toucanets ate flowers revealed that the birds had consumed only corollas, leaving stamens and pistils exposed. Therefore, toucanets may not have affected seed set if pollination had already occurred; birds searching for nectar occasionally remove corollas from flowers without affecting seed set (Baker et al. 1971, Guillarmod et al. 1979). We removed corollas from several Erythrina flowers and found that they separated easily from the remainder of the flower. In addition, some nectar came off within the corolla; both corolla and nectar were palatable to us. We measured 30 corollas which averaged 40.6 ? 9.2 (SD) mm long by 8.0 + 1.4 mm wide and weighed 0.28 ? 0.09 g, which suggested that the male we observed had eaten about 8 g of flowers. Wheelwright (pers. comm.), who has also observed toucanets eating flowers of this species, reported that a flock of toucanets can apparently strip an entire tree in a matter of minutes. All 110 species of the genus Erythrina are pollinated either by hummingbirds or by perching passerines (e.g., Toledo 1974). Based on plant morphology and nectar characteristics, E. lanceolata is classified as a hummingbird-pollinated species, offering a sucrose-rich nectar (Baker and Baker 1982). It would appear unlikely, however, that toucanets commonly pollinate Erythrina flowers, since they usually come in contact with only the outside of the corolla. (2) Saurauia spp. (Dilleniaceae). During the wet season in late afternoon on 3 July 1985, Riley observed one adult (sex unknown) and four juvenile (based on bill size and color) toucanets feeding on the flat white flowers with bright yellow stamens of a Saurauia tree. She focused her attention on a juvenile. This bird ate two whole flowers, moved about 5 cm, and ate another whole flower. After she had observed them for 18 sec, the group left the tree. Thirty of these flowers averaged 11.3 ? 3.3 mm in diameter and 0.31 ? 0.10 g in mass. (3) Mcclenia spp. (Ericaceae). During dry season in late morning on 23 March 1985, Riley observed an adult male toucanet as he ate one whole orange tubular flower of this common epiphyte. The nectar of this flower also tasted sweet and palatable to her. Thirty of these flowers averaged 22.3 ? 1.1 mm long, 5.0 ? 0.4 mm wide, and 0.15 + 0.04 g in mass. Emerald Toucanets have the most varied diet of all fruiteating birds studied in Costa Rican lower montane forests, feeding on fruits of at least 113 different plants at Monteverde (Wheelwright et al. 1984, Riley 1986). Toucanets have also been reported to consume flowers in captivity (Todd et al. 1973). Flower eating is consistent with the idea that frugivorous birds might include a variety of brightly colored food items in their diets (see Herrera 1985). Our observations were made during periods when ripe fruits were readily available, so this is not simply a case of toucanets switching to alternative foods during a shortage of ripe fruit. All reports to date of flower eating by birds from the neotropics concern frugivorous species. Although we have been unable to find data on chemical composition of flowers, flowers in general probably supply a high-energy mixture of lipids, proteins, and carbohydrates, particularly if the entire flower is consumed. If this is true, it is curious that flower eating by frugivorous birds in the tropics has not been reported more often.