Reciprocity, Cooperation, and Altruism

If you wanted to measure the good effects of cooperative behavior in a species, how would you do it? There are many ways, but common ones are to measure the size of the animals in question (to see if they are eating well) or to measure the number of offspring. Positive effects for cooperative behavior would should result in increases in these measures. Not always so, say Russell et al. in Science, largely because the birds are being tricky enough to exploit their neighbors. The Superb Fairy-Wren (superb, I tell you...simply superb!) is a species of bird that raises its young other…