Sugar preferences of the Green-backed Firecrown Hummingbird (Sephanoides sephaniodes): A field experiment

Many flowers associated with hummingbirds (Trochilidae) produce nectar rich in sucrose, a characteristic that reflects innate preferences or the metabolic capacities of their putative pollinators or both. However, studies on nectar sugar selectivity by hummingbirds in the field are lacking. Under natural field conditions, we studied the sugar preferences of the Green-backed Firecrown Hummingbird (Sephanoides sephaniodes), the southernmost hummingbird in the world and a key pollinator in the temperate forest of South America. We considered potential differences between males and females and the influence of environmental temperature on those preferences. To free-foraging Green-backed Firecrown Hummingbirds, we simultaneously offered four different sugar solutions with the same concentration (24% wt/wt): (1) sucrose, (2) glucose, (3) fructose, and (4) a 1:1:1 mixture of these three solutions, as well as a control of pure water. The experimental design involved three replicates per treatment assigned to three different blocks of five feeders each, during eight periods of seven days each. We scored the number of Green-backed Firecrown Hummingbirds feeding on each feeder, the number of consumptions made by each individual, and the amount of sugar (g) consumed per sampling period. Green-backed Firecrown Hummingbirds clearly discriminated against pure water, favoring sugar solutions; of the latter, they preferred sucrose over glucose and fructose. The mixed-sugar solution showed intermediate preference values. Neither sex nor temperature affected sugar preferences. Sugar preferences by the Green-backed Firecrown Hummingbird could influence the nectar composition of the flowers it pollinates through differential selection.