Tracking migration of songbirds is difficult but enlightening
Scientists once assumed, sans evidence of another answer, that songbirds followed a migratory path similar to the flyways of ducks and geese.
But terrestrial birds aren't reliant on the same habitats.
“There really isn't a relatively narrow migration path for them, and they aren't necessarily in the same place in spring and fall,” said Frank La Sorte, a Cornell Lab of Ornithology researcher and lead author of a paper in the Journal of Biogeography.
Songbirds migrate at night, so it's too difficult to set out to track them that way. Because they are generally too small to wear a tracking device, researchers have turned to other technology and volunteers.
They are analyzing thousands of crowd-sourced sighting data reflecting species, not individual birds, submitted to the Cornell Lab's eBird project from 2004 to 2011.
Computer models sorted movement patterns and compared migration routes with seasonal patterns of prevailing night winds, according to information from the lab.
Here are some of the findings:
Most land birds fit into three main groups: Western, 31 species; Central, 17 species; Eastern, 45 species.
Since they are less tied to a single habitat than waterfowl, songbird “flyways” are much more spread out across the continent, and the Central and Eastern groups significantly overlap.
More land birds than waterfowl followed different routes in spring and fall, particularly in the East.
Many species in the Eastern and Central groups take southbound routes far to the east of their northbound routes, a clockwise loop that puts some species over the Atlantic Ocean for part of their trip.
Migratory land birds take advantage of stronger tailwinds in spring and less severe headwinds in the fall, according to the researchers' analysis of prevailing winds.
“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.”
Having a safe place to land for all birds is becoming more important by the decade.
It is a concern to birders as well as bird hunters, particularly since the 1.5-billion-acre boreal forests, circumpolar woods that circle the upper Northern Hemisphere, is under pressure from oil, gas, mining and other industrial hazards to birds.
Boreal forests are primarily cold-hardy trees, most of them coniferous and some deciduous trees.
A new report, “Boreal Birds Need Half: Maintaining North America's Bird Nursery and Why it Matters,” by the Boreal Songbird Initiative, Ducks Unlimited and Ducks Unlimited Canada, call for protecting half of that acreage to protect the habitat of more than 300 nesting and migratory species, estimated at 3 billion birds.
Many of the species are threatened or endangered.
If following the decline in numbers is hard to relate to, follow the money. According to the report, birding-related business generates about $100 billion per year in the U.S. and Canada.
While the boreal forest remains one of the largest intact forests on Earth, it is “also seen as the last great frontier for natural resource extraction,” said Jeff Wells, a Cornell Lab of Ornithology scientist and the report's lead author.
Canada is considering usage policies that will affect the remaining intact 70 percent of the boreal area.
“Decisions are being made today about what will happen over the next 100 years,” Wells said.
In Canada, most land use decisions are made at the provincial or territorial level, said Wells, adding that hundreds of indigenous communities still live in remote boreal areas, where they rely on the land and water for their survival.
Columnist Sharon Wootton can be reached at 360-468-3964 or www.songandword.com.
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