Bird research shows songbirds follow different patterns
One of the pleasant distractions in the spring turkey hunting woods, something to help pass the time when gobblers are not cooperating (which has been often this season), is watching the passage of dozens of little flashes and flits of color – migrating songbirds.
Everything from tanagers to towhees, warblers to wood thrushes are headed north to nest, sometimes traveling thousands of miles from wintering grounds in Central America and South America. And they fill the turkey woods with color and song, a perfect complement to the carpets of wildflowers exploding underfoot.
In this regard, now comes news from the prestigious Cornell Lab of Ornithology in Ithaca, N.Y., that these lightweight fliers – many weigh less than an ounce – really do not follow waterfowl flyways, as typically believed.
“Most of what we’ve known about migration routes comes from ducks and geese,” said Frank La Sorte, a Cornell Lab of Ornithology research associate and lead author of a new paper in Journal of Biogeography. “But terrestrial birds are much smaller and they aren’t reliant on the same kinds of habitats. There really isn’t a narrow migration path for them, and they aren’t necessarily in the same place in spring and fall.”
In short, scientists now are finding out how these featherweights do it. They use elliptical routes that take advantage of prevailing winds to save energy, the lab said this week.
Waterfowl flyways over the years were delineated by compiling leg-band recoveries and hunter records, and those techniques that don’t work for small songbirds, which migrate at night. So work at Cornell tried a fresh approach and crowd-sourced data submitted to the Lab’s eBird project between 2004 and 2011.
Researchers analyzed thousands of sightings to develop, for each of 93 species, an aggregate picture of where a species is during spring and fall migration. Although they weren't tracking individual birds, collectively the sightings gave them an indication of how the species were migrating. Then they used computer models to sort species with similar movement patterns into groups. They also compared migration routes with seasonal patterns of prevailing winds at night.
The study indicated that most land birds fit into three main groups, a Western group consisting of 31 species, a Central group of 17 species, and 45 species in an Eastern group (examples include the Black-throated Gray Warbler, Clay-colored Sparrow, and American Redstart, respectively). The researchers kept the term “flyway” to retain the analogy to waterfowl movements, but they noted these flyways are much more spread out across the continent, and routes in the Central and Eastern groups overlap considerably.
The analysis also revealed that many more land birds than previously realized follow different routes in spring and fall—particularly in the East, where many species cross the Gulf of Mexico in a single overnight flight, according to Cornell.
Unlike waterfowl, which migrate north and south along the same relatively narrow routes, rather like semi-trucks on an interstate, songbirds are more like passenger cars touring back roads. They are less tied to a single habitat than waterfowl, so they can fan out across the continent. Many species in the Eastern and Central groups take southbound routes far to the east of their northbound routes, resulting in a clockwise migration loop that puts some of them out over the Atlantic Ocean on their way to their wintering grounds.
By shifting routes, birds are taking advantage of stronger tailwinds in spring and less severe headwinds in fall, the study found. Tailwinds represent a huge advantage for birds heading back to their breeding grounds, Cornell’s La Sorte said, while finding weaker headwinds in fall allows southbound birds to make the best of a bad situation.
Significantly, the new findings may help refine ideas about how and where to plan for conservation along migratory pathways. “All these species migrate at night, at high altitudes, where we can’t see them,” La Sorte said. “But when the sun comes up in the morning they have to find somewhere to land. So any new knowledge about where they’re traveling is valuable to conservation planners.”
In a related note, it now is known that with a little luck songbirds can live many more years than once thought.
Tom Kashmer, research coordinator for the Sandusky County Park District, last September was banding migrating songbirds and he mist-netted an indigo bunting that already was wearing a band. It turns out that the numbers on the band showed that the same bunting had originally been caught and banded in Ottawa County, just north, in May, 2001, by Mark Shieldcastle, well-known retired Ohio waterfowl biologist and now research director of Black Swamp Bird Observatory.
That makes the Shieldcastle-Kashmer bunting the oldest documented indigo bunting in the wild, far older than one currently listed by Cornell at 8 years and 3 months. Such is the value of banding birds, from ducks to songbirds.