Net intake is the difference between the rates of metabolisable energy gain and energy expenditure during a foraging cycle (W). Efficiency is the ratio of metabolisable energy gain over energy expenditure during a foraging cycle(dimensionless). A foraging cycle included the flying time needed to obtain one pellet, the perch time following these flights and the time for handling and eating a pellet (the latter two were estimated at 2 s, but within reasonable limits these estimates had negligible effect). Computations used data from Table 1, and assumed that MR_flight=20.5 W in the rich and intermediate environment and MR_flight=17.5 W in the poor environment.