Figure A4.

Probability surface of P (choosing x) for different combinations of conspecifics and heterospecifics on feeder x for (a) blue tits and (b) great tits. The curve is plotted for twice the mean group size experienced by individuals of each species (see Fig. 4). The black line represents the contour of P = 0.25, or the threshold above which individuals choose x more than at random. This shows that the values at which this probability threshold is reached (shown by the dotted black lines) does not stay constant as the flock size changes, but scales proportionately, where birds avoid sites below one-third the number of conspecifics and sites below one-half the number of heterospecifics.