How Many Partridges Are Really in that Pear Tree?

This is Scientific American 60-Second Earth. I'm David Biello. Your minute begins now.
There's a partridge in a pear tree, two turtledoves, three French hens, four calling birds, six geese, and seven swans.
Or so goes some the lyrics to the 12 days of Christmas.
But on December 14th, the annual 21 days of the Christmas Bird Count begin.
And it's revealing a lot more about birds than just their numbers.
The effort put together by the Audubon Society since 1900 mobilizes tens of thousands of citizen scientists to get out and count birds.
Last year, more than 70,000 people from the Arctic Circle to Tierra del Fuego tallied some 60 million different birds, and nearly 2,300 different species.
Seems that birder competition drives good science.
Odd things have been noticed in recent times.
More hummingbirds now winter in the U.S.
A relative of colorful puffins known as the razorbill has moved hundreds of miles south in search of food, and many washed up on shore dead from starvation.
But it's not all bad news.
114 years of data show that bird populations continue to rebound in the continental U.S.and icons like the bald eagle are back.
As climate change and other threats shift highly mobile animals like birds, the birders will be watching and helping guide appropriate conservation efforts.
So get out and count!
Your minute is up, for Scientific American 60-Second Earth. I'm David Biello. Thanks for listening.