Nectar intake and foraging efficiency: Responses of honeyeaters and hummingbirds to variations in floral environments

Costa Rican hummingbirds a Lid Austraian honeyeaters respond to an increase in the volume of nectar made available ill tubular flowers by increasing the duration of foraging bouts, the rate at which nectar is ingested, and the energetic efficiency of that process. Enhanced intake is the result of increased nectar capture by the tongue during each lick rather than of any significant change in licking rate. All species react to an increase in floral length by spending more time foraging and reducing nectar intake, short-billed species being most affected. Decreased nectar capture per lick, rather than a change in licking rate, is responsible for this response. Honeyeater foraging times increase and nectar-intake rates decrease when the curvature of flowers is increased, though all but one of the short-billed hummingbird species were relatively insensitive to this change. Hummingbirds harvest nectar with equal proficiency whether foraging at erect or at pendulous flowers, whereas the bouts of honeyeaters are longer, and their nectar-uptake rates lower, when they visit pendulous flowers. Overall nectar-extraction rates of hummingbirds, as measured ill the laboratory, were greater than those of honeyeaters; values for both groups were generally higher than rates recorded in the field. Hummingbird and honeyeater tongues are equally adept at extracting nectar from tubular flowers, though my results suggest that honeyeater tongues would be more effective in situations where nectar is thinly and widely dispersed.