Science First Look

Annual Christmas Bird Count reveals avian trends

Sponsored by the National Audubon Society, the annual winter tally offers an opportunity for ordinary citizens to help gather data on bird populations around the globe.

Delaine Leblanc looks for birds off of La. 20 near Chackbay, La., Monday, as part of the Annual Christmas Bird Count.
Abby Tabor/The Houma Daily Courier/AP
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This year’s Christmas Bird Count is a wrap, with more than 16 million birds already reported by birdwatchers in local events across the Western Hemisphere.

The National Audubon Society’s annual event, now in its 117th year, saw at least 680 regional counts completed in the United States, Canada, and abroad, according to preliminary numbers from the bird conservation organization. The event, where a group of birdwatchers try to spot as many species as they can within a 7.5-mile radius, ran from Dec. 14 to Jan. 5.

Started in 1900 as an alternative to Christmas hunting traditions in England and North America, the Christmas Bird Count has become one of the largest citizen-science events in the world. It has also taken on a second purpose besides curbing a tradition ornithologists in the 19th and early 20th century considered a serious threat to bird populations. Today, the count provides valuable data to ornithologists and researchers.  

"The information collected provides valuable statistics on declines and increases in particular species, geographical shifts in winter ranges, and other indicators of the status of bird populations," Peter Berle, then the president of the Audubon Society, wrote in The Christian Science Monitor in 1986, when the tradition was 40,000 bird-watchers strong.

“But the Christmas Bird Count and the data generated have a deeper importance,” added Mr. Berle. “As birders see the effects of pollution and loss of habitat, they have become more sensitive to the interrelatedness of all life; this is why the National Audubon Society has evolved naturally from a birding group to one of the nation's largest and most deeply committed conservation organizations.”

The National Audubon Society sponsors more than 2,400 local events each year for the Christmas Bird Count, according to the Daily Comet in Louisiana. A volunteer group will spend one day searching a circular area 15 miles in diameter to identify and record as many birds as possible. Audubon researchers and conservationists will then compile the data to assess bird populations.

The bird conservation group is still verifying this year’s data but says at least 16,748,423 birds were identified in this year’s count. If last year is any indication, the final count will be much larger.

In last year’s bird count, nearly 59 million birds were tallied, about 54 million in the United States, with the remaining birds in Canada, Latin America, the Caribbean, and Pacific Islands, according to the National Audobon Society. Of this total number, 2,607 species were tallied, about one-quarter of the world’s known bird species.

These raw numbers have provided valuable data for researchers to look at bird trends over the years. The Christmas Bird Count was important in determining the bald eagle population rebounded after almost being driven to extinction by hunters and the pesticide DDT, according to the Press of Atlantic City. It also showed the merlin, a small falcon, moved its wintering grounds farther north.

The data is also used by federal agencies as an indicator of climate change and how it is affecting populations. In its “State of the Birds 2009,” the US Fish and Wildlife Service found about one-third of the 800 US birds species are in serious decline due to habitat loss, invasive species, and other threats.

In recent years, the Christmas Bird Count has shown bird species are moving northward into New Jersey, William Boyle Jr., a Christmas Bird Count regional editor for the Garden State and Pennsylvania, told the Press of Atlantic City.

"One thing I have seen: There are a lot of southern species – what people in the birding world call half-hardy – that are pushing it to try to spend the winter in New Jersey. More and more of them are staying around," said Mr. Boyle. 

This report includes material from the Associated Press.

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