Abstract
ABSTRACT During flight, hummingbirds achieve the maximum aerobic metabolism rates within vertebrates. To meet such demands, these birds have to take in as much energy as possible, using strategies such as selecting the best food resources and adopting behaviors that allow the greatest energy gains. We tested whether hummingbirds choose sources that have higher sugar concentrations, and investigated their behaviors near and at food resources. The study was conducted at Atlantic forest remnant in Brazil, between June and December 2012. Four patches were provided with artificial feeders, containing sucrose solutions at concentrations of 5%, 15%, 25% and 35% weight/volume. Hummingbird behaviors were recorded using the ad libitum method with continuous recording of behaviors. The following species were observed: the Brazilian ruby Clytolaema rubricauda (Boddaert, 1783), Violet-capped woodnymph Thalurania glaucopis (Gmelin, 1788), Scale-throated hermit Phaethornis eurynome (Lesson, 1832), White-throated hummingbird Leucochloris albicollis (Vieillot, 1818), Versicoloured emerald Amazilia versicolor (Vieillot, 1818), Glittering-bellied emerald Chlorostilbon lucidus (Shaw, 1812) and other Phaethornis spp. C. rubricauda, P. eurynome and Phaethornis spp. visited the 35%-sucrose feeders more often, while the T. glaucopis visited the 25%-sucrose feeders more often. L. albicollis and A. versicolor visited more often solutions with sugar concentration of 15%. C. lucidus visited all patches equally. Three behavioral strategies were observed: 1) C. rubricauda and T. glaucopis exhibited interspecific and intraspecific dominance; 2) the remaining species exhibited subordinance to the dominant hummingbirds, and 3) P. eurynome and Phaethornis spp. adopted a hide-and-wait strategy to the dominant hummingbird species. The frequency of aggressive behaviors was correlated with the time the hummingbird spent feeding, and bird size. Our results showed that hummingbirds can adopt different strategies to enhance food acquisition; that more aggressive species feeding more than less aggressive species; and that the birds, especially if they were dominant species, visited high quality food resources more often.
Highlights
Hummingbirds are specialized birds that consume predominantly nectar, but can consume small arthropods (Cotton 2007)
We described the behavior exhibited by the hummingbirds in the food patches and identified the sugar concentration most visited by the birds
The frequency of aggressive behaviors exhibited by A. versicolor, L. albicollis, P. eurynome and Phaethornis spp. was statistically lower than by T. glaucopis and C. rubricauda; the former species were expelled from the feeders by the latter dominant species, feeding less in the artificial patches
Summary
Hummingbirds are specialized birds that consume predominantly nectar, but can consume small arthropods (Cotton 2007). Sugar concentrations in the nectar of the flowers visited by hummingbirds vary between 20–25% (Roberts 1996), and experimental manipulations revealed that hummingbirds prefer sugar concentrations higher than 35% (Tamm and Gass 1986, Roberts 1996, López-Calleja et al 1997). This preference was observed only when the nectar was collected during repeated licking (Kingsolver and Daniel 1983).
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