Patterns in Floral Nectar Characteristics of Some Bird-Visited Plant Species From Costa Rica

Nectar samples from a wide range of flowers (120 samples, 112 species, 22 families) visited by hummingbirds (subfamilies Phaethorninae and Trochilinae) were collected over a wide range of elevations and environments in Costa Rica. Some species visited are believed to be pollinated principally by perching birds, lepidopterans, and bees, however. We measured sugar composition (% fructose, glucose, and sucrose), daily secretion rates, and sugar concentration. In general, sugar compositions of all hummingbird nectars were found to be highly clustered toward the high-sucrose end of the composition spectrum and not significantly different from sugar compositions of other hummingbird nectar assemblages from northwestern Mexico and the southwestern United States. Significant correlations were detected between elevation and the percentage of fructose and of sucrose in the nectar, with the fructose percent positive and the sucrose negative. These correlations were found to be due to both elevation and hummingbird-group effects. Daily secretion rate and sugar concentration were both negatively correlated with elevation. Discriminant analysis indicated that nectar sugar concentration and daily secretion rates together could usually predict whether a species was pollinated by hermit (Phaethorninae) or nonhermit (Trochilinae) hummingbirds and could often predict which eco-morphological group of nonhermits.