The Cornell Lab of Ornithology has not only documented the migratory movements of more than 100 western hemisphere bird species but created a fascinating animated map which shows the approximate location of each throughout the year.
This is the first time data of this sort has been compiled on such a scale. It includes such extreme migrations as that of the Lapland longspur, which travels well into the Arctic Circle in July and August, and the dark-faced ground-tyrant, which makes its way to the tip of Tierra del Fuego from November through February.
There are others that migrate from Brazil and other South American countries all the way north to central Canada, a distance of 7,000 miles or more.
“We used millions of observations from the eBird citizen-science database,” said lead author Frank La Sorte, a research associate at the Cornell Lab. “After tracing the migration routes of all these species and comparing them, we concluded that a combination of geographic features and broad-scale atmospheric conditions influence the choice of routes used during spring and fall migration.”
(You can access a second map here, which will provide an index through which you can follow different species on their year-long route.)
Perhaps the most unusual migration is that of the purple sandpiper. This species winters near the eastern tip of Cape Breton Island, in the Canadian Maritimes, than spends its summer on Baffin Island, in far northern Canada.
While not limited to Canada, in North America the species’ breeding ground is the northern tundra on Arctic islands in Canada. They also breed in Greenland and northwestern Europe, perhaps in part to cement their role as ornithological tough guys. Anyone or anything that purposely winters in the Canadian Maritimes and also spends time in Greenland has my respect.
It appears, according to Cornell’s interactive map, that purple sandpipers have little interaction with other species, as none have migratory patterns that bring them within a couple hundred miles of the small shorebirds.
An important discovery of the study is that bird species that head out over the Atlantic Ocean during fall migration to winter in the Caribbean and South America follow a clockwise loop and take a path farther inland on their return journey in the spring, La Sorte said. These include bobolinks, yellow and black-billed cuckoos, Connecticut and Cape May warblers, Bicknell’s thrush, and shorebirds, such as the American golden plover.
“These looped pathways help the birds take advantage of conditions in the atmosphere,” he added. “Weaker headwinds and a push from the northeast trade winds as they move farther south make the fall journey a bit easier. The birds take this shorter, more direct route despite the dangers of flying over open-ocean.”
The study found the spring migration path follows a more roundabout route but the birds move faster thanks to strong tailwinds as they head north to their breeding grounds.
Species that do not fly over the open ocean use the same migration routes in the spring and fall. Geographic features shaping this pattern include mountain chains or isthmuses that funnel migrants along narrow routes, according to the study.
(Screen grab from Cornell migration study, showing location of different species on April 9. The purple sandpiper is the blue dot seen in the far eastern reaches of Canada.)