As you may know, the Common Cuckoo and Oriental Cuckoo are brood parasites. That is, they lay their eggs in the nests of other birds, leaving their chicks to be raised by the unsuspecting foster parents. A cuckoo chick in the nest reduces the likelihood that the original chicks will survive, because female cuckoos time their egg-laying so that their chicks hatch first...and then shove the other eggs out of the nest.
In areas where brood parasites are common, host species often develop coping strategies. Some birds hide their nests, or nest at different times. Some attack the brood parasite before she lays her egg or abandon the nest once she's laid it. Others pierce the parasite's egg and toss it out of the nest.
But what about birds that live where brood parasites aren't common? A new study from the University of Illinois and the University of Tennessee, Knoxville shows that an invasion of cuckoos from eastern Russia might cause significant losses among Alaskan birds. Professors Mark Hauber and Vladimir Dinets led the study to learn what Alaskan birds do—or don't—know about coping with brood parasites.
Common Cuckoos and Oriental Cuckoos are occasionally sighted in Alaska. Most likely, they've gotten there from Beringia in eastern Russia. While there isn't solid evidence that cuckoos are breeding in Alaska, Hauber says "it's likely already occurring."
Researchers put two types of fake eggs into the nests of more than two dozen songbird species in both Siberia and Alaska. (The fake eggs resembled varieties of cuckoo eggs.) Common Cuckoos and Oriental Cuckoos have advanced into Siberia and now breed near the Bering Strait; in comparison, Alaska is new territory. The researchers made sure to test each nest with each kind of egg. After the usual losses from predation, they had data from 62 nests of 27 bird species.
Fourteen out of 22 Siberian nesting pairs rejected the fake eggs, but only a single one of the 96 Alaskan pairs rejected the fakes. Hauber suspects this result indicates that Siberian songbirds have encountered cuckoos long enough to develop coping behaviors, but he's worried about Alaskan songbirds. "The North American hosts have no defenses against invading cuckoos. They will be parasitized."
We hope that future ornithologists will follow up to find out how the Alaskan songbird population distribution has changed—and whether any of them have wised up about cuckoos.
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