The battle over who cares for the kids has played a key evolutionary role in deciding whether different species of shorebird are monogamous or polygamous, according to new research in the journal BioScience.

A demanding youngster means that parents are more likely to stay together to help rear their young, yet those with more hardy offspring are likely to battle it out to see who gets to leave the nest.

Played out over evolutionary time, it is this childcare tug-of-war which has shaped the varied breeding systems found amongst the world's shorebirds, say researchers.

Scientists from the universities of Bath, Bristol and Imperial College London (all UK) focused on the Kentish plover (Charadrius alexandrinus) to help investigate the influences on the shorebirds' breeding systems.

The Kentish plover is particularly interesting because whilst some pairs are monogamous, in other pairs either the male or female can be sequentially polygamous, mating several different times throughout the breeding season and leaving the abandoned partner to raise the chicks.

The scientists also found that whilst both males and females are equally adept at raising the offspring, the female parent is more likely to leave childcare responsibilities to her partner if there is a high ratio of unpaired males around. Mathematical modelling showed that if the sex ratio was reversed, so that there were more females than males, it would be likely that males would fly the nest in search of a mate.

The scientists also discovered that unpaired females would find a new mate faster (on average less than two days) after deserting the nest than males (average 12 days).

"Having systems of independent self-feeding young, compared to those that require feeding by the parents, opened the possibility for the evolutionary divergence of breeding systems to those where either females or males had more than one mate," said Dr Tamas Szekely fro
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Contact: Andrew McLaughlin
a.mclaughlin@bath.ac.uk
44-012-253-86883
University of Bath
10-Oct-2006