The National Audubon Society's 116th annual Christmas Bird Count is underway, which means it's the perfect time to unleash your inner birder and take a gander at migratory bird species as they fly south for the winter.

Every winter, citizen scientists participate in bird-counting events across North America, from mid-December until early January, to collect data on bird migrations for the National Audubon Society. This year, there will be bird counts in countries all over the Western Hemisphere, including the United States, Canada, Mexico, Guatemala, Nicaragua, the Dominican Republic and several others listed on Audubon's website

The Christmas Bird Count, which began last week and runs through Jan. 5, is the longest-running wildlife census in the United States. Data from the counts give scientists insight into birds' migratory movements that researchers would never otherwise have, such as how bird ranges have been shifting over time. 

Databases created from the Christmas Bird Counts have contributed to several hundred research papers over the years. "[In] the late '70s to the early '80s, researchers began to embrace citizen science data sets," said Geoff LeBaron, director of the Christmas Bird Count for the National Audubon Society. In particular, the project allows scientists to follow interesting migration trends and range shifts for hundreds of different bird species in North America, LeBaron told Live Science.

How the bird counts work

Each count encompasses a circular area that is 15 miles in diameter, which has been the standard since the mid-19th century, LeBaron said.  

There are also two ways to participate in the bird counts: as a field observer, someone who actually walks around and counts birds; or as a feeder watcher, someone who makes observations about the different bird species visiting their home bird feeder, LeBaron told Live Science. Both types of volunteers offer valuable but different data for scientists to use.

Once one count is completed, the collected data are compiled and sent to the National Audubon Society so that scientists there can compare those numbers to other counts coming in from other regions of North America.

"There are some species of birds that could be seen on most Christmas Counts in North America," LeBaron said. Birds such as the American robin, starling, pigeon and black-capped chickadee are all likely to be seen, he said.

LeBaron also mentioned that birders are more likely to see Eastern bird species farther west than they are to see Western birds farther east because Eastern birds are migrating down from Canada while Western birds are heading down toward Mexico and Central America. However, there are some differences during El Niño years. For example, LeBaron speculated that recent sightings of a painted bunting in Brooklyn, New York, are likely due to weather anomalies from the current El Niño. (Usually, this bird lives in the southeastern U.S. and flies to Mexico for the winter, according to the Cornell Lab of Ornithology.)

Whooooo goes there?

What about snowy owls? Sightings of these majestic creatures have been highlights of past Christmas Bird Counts, and while it's possible that some people may spot them this year, there is no guarantee, LeBaron said.

"The snowy owl is an irruptive species," he said. This means that while the owls may not be consistently present in a particular area, there are seasons when there are huge spikes in snowy-owl sightings, including in places as far south as Bermuda. (In 2014, 22 snowy-owl sightings were reported in New York City alone.)

Scientists with Project SNOWstorm, which began with the historic owl irruption of 2013-2014, started to piece together some of the behaviors that might explain these seemingly random sightings. The scientists used backpacks equipped with GPS trackers to follow snowy-owl migration patterns, and their research suggested that snowy owls may be following the movements of lemmings, their main source of food.

Snowy owls have been seen in parts of Canada already, LeBaron said, but it's not clear whether this year's counts will feature as many sightings of the owls as there were in 2013 and 2014.

But regardless of whether you want to catch a glimpse of a rare bird or just go outside and enjoy an outdoor winter activity, something that's great about the Christmas Bird Count is that anyone can participate. "You don't need to be an experienced birder," LeBaron said. "Some of the most important data [come from] looking for the birds that are supposed to be there [not rare bird sightings]."

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