(University of Michigan News)
“The idea is, the parasites don’t have the limitations that normal birds have, so the prediction is that they would lay more eggs.” When Payne compared the ovaries of parasitic Black Cuckoo females with those of nonparasitic species to see how many eggs they had laid in their lifetimes, he found that the prediction held true.
In more recent work, Payne and Sorenson have tried to understand how cuckoos became parasitic in the first place. The question puzzled Charles Darwin, who thought the behavior might have arisen from species that occasionally lay eggs in other birds’ nests, but also raise their own broods, as Yellow-billed and Black-billed Cuckoos do. Another parenting pattern that might lead to brood parasitism is cooperative breeding, seen in cuckoos such as Anis and the Guira Cuckoo. In these birds, several mated pairs share a nest where they all lay eggs and care for the young. But it’s not all peace and love in the avian communes. Sometimes a female pitches out nestmates’ eggs when she lays her own.
Payne and Sorenson’s analysis, which combined traditional morphological methods with Payne’s song recordings and Sorenson’s molecular genetic analysis, showed that brood parasitism originated more than once in the cuckoos; not all parasitic species are from a single lineage. And their analysis confirmed what Darwin hypothesized: the trait seems to have come from the habit of occasionally laying eggs in another bird’s nest, not from cooperative breeding.
And I thought penguins were bad.