How to detect a cuckoo egg: A signal-detection theory model for recognition and learning

This article presents a model of egg rejection in cases of brood parasitism . The model is developed in three stages in the framework of signal-detecti on theory. We first assume that the behavior of host females is adapted to the relevant parameters concerning the appearance of the eggs they lay. In the second stage, we consider the possibility that females make perceptual errors. In the final stage, females must learn to recognize their own eggs through an imprinting process. The model allows us to make a number of pred ictions concerning the egg types that should be rejected in different circu mstances: egg rejection should increase as the parasitism rate increases an d egg mimicry deteriorates; host females' erroneous ejection of their own e ggs should be expected for intermediate levels of egg mimicry but not for v ery good or very poor mimicry; host females would benefit most from learnin g to recognize their own eggs when individual variability in egg characteri stics is much lower than the population variability; and, when egg mimicry is poor or individual variability is very low, females should attempt to im print on the first egg they lay, before they can be parasitized, but, when mimicry is good and individual variability is relatively high, females must use an extended learning phase. The model provides a framework to study ho w the enigmatic acceptance of parasitic eggs can be explained by adaptive d iscrimination mechanisms.