Cost increases (runway length between the two ramps and water depth) with increasing test number for the 3 feed treatments.

Water depth is based on percentage of the mean length of the birds' legs, from the ground to top of the hock, for each food treatment. The initial water depth was 1/6th of the average leg length and increments of 1/6th were then made at successive tests so that in the last two tests the water was deeper than the birds' legs were long, meaning that her body was getting wet.