‘Good Decoys’ Sexual dimorphism and differential predation

We have two female common pheasants in our garden at the moment. I can tell they are female as they are brown and, for such large birds in this context, surprisingly inconspicuous.

The male pheasant is larger and more conspicuous, and plays no part in the raising of the young.

Male pheasant from Wikipedia

I read The Selfish Gene a long time ago and am aware of the standard explanations for sexual dimorphism in which either the male demonstrates good genes by exaggerated, biologically costly plumage or similar – the handicap principle, or the females chose mates who are likely to result in other descendants who will also be chosen by other females as mates – the sexy sons hypothesis.

It is acknowledged that increased colouration in prey species can increase risk from predators – see, for example, Møller AP, Nielsen JT (2006). “Prey vulnerability in relation to sexual coloration of prey”. Behavioral Ecology and Sociobiology. 60 (2): 227–233. doi:10.1007/s00265-006-0160-x. S2CID36836956. This appear just to be something which is noted, as part of the cost of reproductive success.

I have an additional hypothesis, applicable only to prey species, which I am calling the Good Decoys hypothesis. In this case males are selected because, although they may play no part in raising their offspring they can increase the survival chances of their progeny by the male being predated (killed by predators) more than the females.

Assuming both sexes occupy the same habitat, and a constant predation rate for the species overall, if there is a group of males who are then then killed (post mating) more frequently than the females then although their survival rate will be lower, that of their progeny will be higher as the females survive to sit on the nest, feed the young etc.

In anthropomorphic terms, when choosing a mate, the female pheasant may not actually be thinking ‘what a handsome colourful male’, but ‘If a fox was hunting in the area it would find and eat him before it found me’


  1. So is this the same principle as the male praying mantis, just cutting out the predator bit?

    1. Similar certainly, the point which Dawkins makes it that evolution selects for the good of the species (or more specifically a set of genes), rather than the individual.

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