Fig. 4. Intake rate in experiment 2 as a function of gizzard size class (values are means ± S.E.M.). Open circles indicate a soft diet of unshelled mussels was offered; closed circles, a hard diet of with-shell mussels was offered. The broken line gives observed handling rate (1/H). The broken diagonal line gives the intake rate for with-shell mussels predicted from shell mass, gizzard size and regression coefficients obtained in experiment 1. The grey bar gives the postulated maximum metabolizable energy intake rate [average of Kirkwood (1983) and Kvist and Lindström (in press)].