Eastern birds fly west to nest
New research confirms second breeding season for Yellow-billed Cuckoo, Orchard Oriole
Published: June 22, 2012
Researchers who reported in 2009 that five North American songbird species squeeze in a second breeding season each year in western Mexico after first nesting in the United States or Canada have reevaluated the finding after studying specimen records and egg collections.
The behavior, dubbed migratory double breeding, has been ruled out for two of the species — Cassin’s Vireo and Yellow-breasted Chat — and has been called into question for a third, Hooded Oriole. For Yellow-billed Cuckoo and Orchard Oriole, however, the new data bolster the argument that the birds breed twice a year in far-flung locations.
University of Washington biologist Sievert Rohwer and colleagues described the updated research in the February issue of The Condor.
The cuckoo appears to breed once in eastern North America in May and early June and then flies west to nest again in the western U.S. and northwestern Mexico.
Orchard Oriole, which also breeds in the eastern states beginning in May, has been found nesting in northwestern Mexico in late May and early June, as well as in July and August. Rohwer’s explanation: Orioles whose first nests fail may quickly fly to Mexico to try again, and the birds that complete the nesting cycle in the east then migrate to Mexico and breed a second time in mid-summer.
The behavior may explain the oriole’s “exceedingly early fall migration,” he writes.