Conspecific brood parasitism (CBP) is a reproductive strategy in which a female lays eggs in the nest of conspecifics without providing any subsequent parental care. The parasite gains the benefits of emancipation from parental care, whereas the host suffers the costs of rearing genetically unrelated offspring. This behavior occurs in approximately 236 species of birds encompassing 16 different avian orders.
CBP is more likely to evolve under a set of ecological and behavioral conditions. Of the 236 species of conspecific brood parasites, 57% of those species breed colonially. CBP is also more likely when nesting sites are a limiting factor, which is common in non-excavating hole nesters. Finally, CBP is expected to occur at a higher rate when host nests are available for extended periods of time, like in species that lay large clutches of eggs. Interestingly, Burrowing Owls fit each of these criteria in a number of ways. They breed semi-colonially, they nest in underground burrows that they do not dig themselves, and they can lay up to 14 eggs in a clutch.
Because the costs of raising offspring are great, selection should favor the evolution of behaviors to defend against investing in genetically unrelated offspring. Defense behavior could include recognition and/or rejection of the parasitic egg, desertion of the parasitized clutch, or changes in parental investment.
The most effective way to evaluate if and how CBP has shaped the nesting behavior of Burrowing Owls is to experimentally parasitize nests with the eggs of conspecifics. My study will focus on examining the responses of free-living Burrowing Owls to experimental CBP by adding or switching eggs into host nests. Through a series of field experiments I will record any changes in owl behavior at nests where experimental parasitism has occurred. I will record and characterize any incidence of egg recognition or removal, nest or clutch desertion, or changes in parental investment.