Short‐term energy regulation in nectar‐feeding birds: the response of Whitebellied Sunbirds (Nectarinia talatala) to a midday fast

Abstract

Summary Small nectar‐feeding birds have high energy turnover and must respond rapidly to changes in food concentration or feeding opportunities. A previous study showed that Rufous Hummingbirds (Selasphorus rufus) were unable to adjust their intake rates after a midday fast and thus ended the day with energy deficits that necessitated the use of torpor. We examined the ability of Whitebellied Sunbirds (Nectarinia talatala) to cope with a similar loss of foraging time (lights out from 10.00 h to 12.00 h). During the experiment, birds were kept at 10 °C and fed 20% w/w sucrose solution. In contrast to hummingbirds, sunbirds increased their rate of afternoon feeding following the fast, consuming 14·3 ± SD 10·0% (n = 8) more than on the afternoon of the control day, and maintaining evening body mass at control levels. However, morning body mass on the third day was significantly lower than on the previous 2 days, indicating that compensation for reduced feeding time was probably incomplete. Nectar‐feeding birds show varied and flexible responses to energy challenges.