But while a cuckoo hatchling thrives by muscling its host's eggs out of the nest and hogging all the food, a new study by biologists from the University of California, Berkeley, and the University of Cambridge in England shows that cowbird chicks survive with a less ruthless strategy.
A cowbird chick instead joins its nestmates in a chirping chorus that brings in more food than one noisy cowbird chick could demand from its host parents. By eating more than its share, the researchers found, the cowbird chick actually grows faster when sharing the nest and food with two host chicks than it does when all alone in the nest.
"The cowbird alone is incapable of bringing in enough parental resources - basically food - to be able to grow optimally," said Mark E. Hauber, a Miller Research Fellow in UC Berkeley's Museum of Vertebrate Zoology. "When it has nestmates, the whole nest brings in more parental care, because there is more begging altogether, and so the parents attend the nest more. But the cowbird monopolizes the feeding attempts by the parents. In these experiments, instead of getting 33 percent of the feedings that a brood of two host chicks and one cowbird chick gets, the cowbird actually got over 50 percent of the feeding. So, it grew better than when it was living alone."
Hauber, along with University of Cambridge biologists Rebecca M. Kilner and Joah R. Madden, published the findings in the August 6 issue of Science. Hauber will take a faculty position at the University of Auckland in New Zealand at the end of this year.
Though reviled by bird lovers, cowbirds have proved spectacularly successful, having expanded their range from the Midwest to the entire United States over the past 400 years. This is partly due to their p
Contact: Robert Sanders
University of California - Berkeley