Feeding Behaviour and Energetics of the Western Spinebill, Acanthorhynchus Superciliosis (Aves: Meliphagidae).

Acanthorhynchus superciliosis shows diurnal variation in bodyweight, with morning (dawn) values significantly lower than evening (dusk) weights. These weights are stabilized by birds fed on nectar 0.82 and 0.37 mol/litre, although some difficulty seems to be experienced by birds given 0.20 mol/litre. Regardless of nectar strength, birds exhibit temporal variations in feeding behaviour, with feeding times and rates of nectar intake greater for the first 60 to 90 min of each day than later. The frequency of visits to the source of nectar is higher in the morning and at midday than in the late afternoon. In general, A. superciliosis responds to a decrease in nectar concentration by accentuating the above variations and increasing its overall rate of nectar intake, frequency of visits to the nectar source and the time spent feeding. These changes permit birds to increase their energy intake, although it would seem that, particularly for birds drinking 0.20 mol/litre, the energetic cost incurred may more than offset the additional energy gained.