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| Dunnock - Prunella modularis |
Dunnocks are a species of bird where the females are polyandrous. This means they mate with multiple males during one breeding season. The level of paternal uncertainty increases as males are unsure of how many other males the females has already mated with. From this the term sperm competition arises. Male dunnocks will peck at a females cloaca, urging her to eject the sperm from a previous male before mating.
Because of this method of competition between the males they invest little in extravagant plumage and so look very similar to the females.
A great video that explains this reproductive strategy can be found following the link below:
http://bbc.in/1DNwT3M
Despite this strategy being rather uncommon it can even be found in certain human groups. Females ensure resources from different males to her offspring by copulating with multiple males as each male knows there is a chance the offspring could be his own. This seems like quite an effective strategy but only if there is no way of the male finding out exactly which are his offspring. It relies on good female deceit, in the 'selfish gene' terms.
(The Selfish Gene by Richard Dawkins is a great book - read it!)
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