Egg Characteristics Affecting Egg Rejection
We have reviewed the most important results relating to particular egg characteristics responsible for recognition and subsequent rejection by hosts of brood parasites. Hosts remove a foreign egg after determining that it differs in one or more parameters. In turn, brood parasites have often evolved various mechanisms to confuse host defences and prevent egg recognition. The most conspicuous one is egg mimicry—imitation of the appearance of host eggs. We evaluate and discuss egg rejection experiments, particularly from a historical perspective, and the use of cameras in experiments. Further, we describe assessments of egg mimicry, and in particular we focus on the role played by particular characteristics in discrimination including egg colour, spottiness, chromatic versus achromatic cues, the role of UV spectra, the blunt egg pole, and the shape and volume of the parasitic egg. In addition, we discuss how research methodology and the application of experimental approaches to studying avian vision have affected studies on egg discrimination.
We are grateful to Manuel Soler, Daniel Hanley, and Phil Cassey for their helpful comments and suggestions. This work was partly supported by the Grant Agency of the Czech Republic (grant no. 17-12262S to MH) and the National Research Foundation of South Africa (grant 96257 to MIC).
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