Interruptions in nectar availability: responses of White-bellied sunbirds (Cinnyris talatala) and Brown honeyeaters (Lichmera indistincta)

Abstract

Limited food availability may disrupt the energy balance of animals, and small birds with high metabolic requirements and relatively low capacity for fuel storage may be particularly affected. The active lifestyle of nectar-feeding birds necessitates frequent feeding, and energy is accumulated throughout the day to sustain the birds during the night. To investigate how these birds cope with lost feeding time, we exposed captive whitebellied sunbirds (Cinnyris talatala) and brown honeyeaters (Lichmera indistincta) kept at 10°C to a 2 h fasting period during the day. Birds were fed a 0.63 M sucrose solution for the rest of the day. Food intake increased following the fast, relative to uninterrupted feeding. A comparison with the maximal food intake predicted by a digestive capacity model showed that both species fed at maximal levels in the hour following the fast. Although the short-term feeding pattern of honeyeaters was not investigated, sunbirds increased the duration of meals immediately after the fast, followed by a non-significant increase in meal frequency. In contrast to published data for hummingbirds, these two passerines accumulated energy at higher rates after the fast compared to a control day. However, food intake over the whole day was lower on the fasting day and birds weighed less in the evening compared to the control, indicating that the compensation of energy intake and accumulation was incomplete. Our study demonstrates that two phylogenetically distinct nectarivorous avian taxa show similarities in their response to fasting periods, possibly due to similar feeding behaviour and physiological constraints.