Energy balance in the Whitebellied Sunbird Nectarinia talatala: constraints on compensatory feeding, and consumption of supplementary water.

Summary 1. Avian nectarivores consume a simple food which is generally dilute, but may vary widely in concentration and thus in water content. 2. Energy intake over 24 h was investigated in the Whitebellied Sunbird Nectarinia talatala (A. Smith) (mean mass 9·3 ± 1·0 SD g, n = 7) fed a wide range of sucrose concentrations (0·07–2·5 m), with and without access to supplementary water. 3. On diet concentrations between 0·25 and 2·5 m sucrose, birds showed perfect compensatory feeding by adjusting volumetric intake to maintain constant energy intake. 4. However, reduced intake on the two lowest concentrations of 0·07 and 0·1 m meant that the birds could not meet their energetic requirements and lost mass. We propose that physiological constraints associated with ingestion of large volumes of preformed water restrict intake at these very low concentrations. 5. Drinking of supplementary water varied greatly among individuals, but increased as diet concentration increased. This free water consumption effectively diluted the most concentrated diets of 1·5–2·5 m sucrose to an average value of 1·05 m, thus providing an indirect assessment of the birds’ concentration preferences. [ABSTRACT FROM AUTHOR]