Trapliners in the Trees: Hummingbird Pollination of Erythrina Sect. Erythrina (Leguminosae: Papilionoideae)

Abstract

Erythrina sect. Erythrina comprises 36 species of hummingbird-pollinated trees and shrubs, distributed principally in Mesoamerica. Avian floral visitors-including nectar thieves as well as pollinators-were observed at 17 populations of 13 species in southern Mexico and Costa Rica. Legitimate pollinators were all hummingbirds with long bills and non-territorial foraging behavior, including in particular two species of Heliomaster. Nectar thieves included a variety of short-billed hummingbirds and passerine birds. Measurements of nectar volume, sugar concentration, and flowering behavior indicate that the caloric value of nectar in open flowers produced by one tree per day is insufficient to support a single hummingbird's energetic requirements; therefore, territorial defense by a hummingbird of a single tree is precluded. The traplining hummingbirds appear to be effective agents of pollen flow among conspecific trees in the typically low-density Erythrina populations. The pollination system of sect. Erythrina is a canopy-level analogue of the high-reward traplining systems involving hermit hummingbirds and understory plants such as Heliconia (Musaceae).