Fig. 1. Behavioral responses of sunbirds to varying sucrose concentration in food. (A) The rate of sugar intake did not increase significantly with sucrose concentration (r_s=0.12, P=0.49, N=35). Mean sucrose intake was 77.17±3 mg h^-1 (17.94±0.7 kJ day^-1). (B) Volumetric food intake rate declined significantly with dietary sucrose concentration (F_1,29=107.0, P<0.0001). The relationship was well described by a power function (r²=0.76) with an exponent that was not significantly different from 1.0 (t=-1.52, d.f.=33, P>0.1). Changes in food energy density from 0.292 mol l^-1 to 1.168 mol l^-1 sucrose led to an approximately 3.5-fold variation in food (and thus water) intake. The right-hand axis shows food intake in multiples of body mass (5.74±0.07 g, N=4) per 14 h. At low sucrose concentrations, sunbirds consumed 0.8-2.2 times their body mass in food in 14 h of daylight.