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We found a pheasant laying an egg in a duck's nest. Is this common?

Sent in by Tessa Mann, Salisbury

Many species of birds are known to lay eggs in nests other than their own. The purpose of this is for the female to spread her genes rather than have 'all the eggs in one basket'. If anything happens to her own nest, at least one chick has the change of survival elsewhere, carrying the female's genes with it.

This kind of brood parasitism works best if birds lay the egg in the nest of another bird of their own kind, and is well documented in birds like starlings. Where eggs are laid in nests of wildly different species, the chance of success must be fairly low. For instance, if a robin was to lay in the nest of a greenfinch, the chick would not receive the correct food and would be unlikely to survive.

In addition to nests of their own kind, pheasants often deposit eggs into nests of other species, including partridge and mallard. Whether this is by design or by accident, can be difficult to figure out. While a partridge is a good match, both in terms of incubation time of the eggs and the general habits of the birds, a mallard seems a completely crazy choice, and common sense says it has got to be a mistake.

Pheasants incubate their eggs for 23-28 days, and so this egg would hatch at the same time or even before the mallard eggs. However, this is where the problems start. The mallard will lead her newly hatched brood to a convenient piece of water within hours of them all hatching, and since the pheasant chick will not be able to follow its foster mother into the water, it is unlikely to survive on its own for any length of time. I can just imagine the frustration of the mother duck when 'one of her chicks' is refusing to go for a swim....!

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