Thanks to the Lab of Ornithology for this:
By Gustave Axelson; Illustrations by Jillian Ditner
Part of the magic of migratory birds is their annual disappearing act—one autumn day there might be an oriole in a treetop, and the next day it’s gone, not to be seen again until spring.
Back in the 17th century, scientists had lots of ideas about where birds go during winter in the Northern Hemisphere, including one theory that they migrate to the moon. Today we know Neotropical migratory birds are intercontinental travelers, chasing summer as they leave the North for the warmer weather and longer days of the New World tropics.
Birders in the U.S. and Canada are accustomed to saying that birds spend the winter down south, but because the seasons are reversed on either side of the equator, scientists prefer to use the term nonbreeding season. An ornithologist’s year is comprised of four parts: prebreeding (spring) migration, breeding season, postbreeding (fall) migration, and the nonbreeding season.
But not all parts of a bird’s annual cycle are created equal. A Baltimore Oriole may spend five months from November to March in its nonbreeding-season range, more than twice as long as they live in their breeding range.
Scientists may not believe birds are moon travelers anymore, but for most of the 20th century they had only vague notions of where birds go on migration. In the old printed field guides, range maps showed Baltimore Orioles overwintering anywhere from Mexico to Colombia. For the past 15 years, the Cornell Lab of Ornithology’s eBird Science team has been hard at work on the next generation of range maps. Through advances in big-data supercomputing, eBird is melding the observations of 120,000 birders with NASA satellite imagery to show precisely where birds go during all four parts of their annual cycle—including a nonbreeding-season map that shows most Baltimore Orioles overwintering in the core of Central America.
These eBird maps hold answers to one of humankind’s age-old questions: Where did the birds go? As it turns out, that oriole could now be at a backyard fruit feeder eating bananas, bringing joy to a family in Costa Rica as it gains strength for the journey back north.
Forest Birds Of The North Become Forest Birds Of The South
Though Neotropical migratory birds fly thousands of miles south during the nonbreeding season, they are often seeking climatic niches and habitat conditions similar to the places they left up north.
Read the whole article here.