Dissertation Research: Costs and Benefits of Intraspecific Brood Parasitism

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Providing parental care to offspring is the usual mode ofnurturing in birds. However, in a variety of species, some females lay eggs in the nests of other individuals of their own species, which then rear the offspring. There is increasing evidence that this intraspecific brood parasitism is a widespread phenomenon in birds. However, the adaptive significance of this behavior remains unclear. For almost all of the seventy odd species where intraspecific brood parasitism been documented, the identity of the parasitic females, or what they gain by laying eggs in the nests of other females, is unknown. The widespread occurrence of intraspecific brood parasitism raises some fundamental questions about the costs and benefits of providing parental care to offspring in particular, and about the optimization of life history strategies in general. Tounderstand the ecological and evolutionary significance ofintraspecific brood parasitism in birds, a population of American coots in central British Columbia will be studied. Brood parasitism is common in this population and nearly a quarter of all nests were parasitized in 1987. Research to date has revealed that most parasitic females are territorial birds with nests of their own. Thus, parasitic females can be trapped at their own nests, individually marked, and their laying histories can be followed across years. The costs and benefits of brood parasitism to these parasitic females, and the behavioral, demographic and ecological factors associated with the behavior will be examined. Detailed studies like this are necessary if the broad patterns of intraspecific parasitism are to be understood.