FIELD METABOLIC-RATE AND WATER FLUX OF NECTARIVOROUS HONEYEATERS

Field metabolic rate (FMR) and water influx of New Holland honeyeaters (Phylidonyris novaehollandiae), eastern spinebills (Acanthorhynchus t enuirostris) and a crescent honeyeater (P. pyrrhoptera) were measured by the doubly labelled water technique. New Holland honeyeaters had ju st finished breeding and were beginning their summer moult. They range d in mass from 15.4 to 21.0 g (mean = 17.3 g, n = 12) and had FMRs ave raging 8.8 mt CO2 g(-1) h(-1) or 77.6 kJ day(-1), which was 2.8 times their measured basal metabolic rate (BMR). Their water influx rate ave raged 10.7 mL day(-1). Eastern spinebills were still feeding young and had yet to begin moulting. They ranged in mass from 8.0 to 10.7 g (me an = 9.7 g, n = 6), had FMRs averaging 10.9 mL CO2 g(-1) h(-1) or 52.9 kJ day(-1) (2.5 times their measured BMR), and had an average water i nflux rate of 8.7 mL day(-1). FMR and water influx of a single 14.6-g crescent honeyeater, which was in late primary moult, were 75.9 kJ day (-1) (2.7 times measured BMR) and 12.5 mL day(-1). The FMR of New Holl and honeyeaters varied inversely with mean standard operative temperat ure (T-es) calculated for values of T-es below 20 degrees C as follows : FMR (kJ day(-1)) = 134 - 5.47 T-es (n = 12, r(2) = 0.52). Honeyeater FMRs were much lower than would be predicted allometrically for hummi ngbirds of the same mass, reflecting the honeyeaters' low-cost foragin g tactic of consuming nectar while perched.