An article in the October 2006 issue of BioScience, the monthly journal of the American Institute of Biological Sciences (AIBS), describes evidence that conflict between male and female shorebirds over which member of a breeding pair will raise their young has had a profound influence on the evolution of breeding systems in these birds. The article, by Tams Szlely, Gavin H. Thomas, and Innes C. Cuthill, likens the conflict to a tug-of-war played out over evolutionary time.

Shorebirds have varied breeding systems. Females care for the young in some species, males do in others, and in many, the chore is shared. In the Kentish plover, which the authors studied in detail, either the male or the female in a pair may desert, leaving the other partner with the task of raising the young alone.

The authors, at the University of Bath, Imperial College, London, and the University of Bristol, all in the United Kingdom, used a combination of experiments and mathematical modeling to analyze the decisions that Kentish plovers make while raising their chicks. Modeling suggested a rationale for the finding that females are more likely to desert if there are local unpaired males: that tendency emerged as a strategy likely to persist in evolution. Further analyses used molecular and other data to examine the evolution of breeding systems in a variety of shorebirds. These studies suggested that in species with chicks that need a lot of parental care, cooperative rearing is more likely to persist. In species with young that become independent early, either males or females are likely to desert their partners.