(AP) — Kansas and Missouri residents will be out during the next three weeks counting the birds in their states.

It’s part of an annual national effort that began more than 100 years ago, called the Christmas Bird Count.

The count began Dec. 14 and will continue through Jan. 5. Bird enthusiasts plan gatherings or individuals simply count the number of birds they see in their backyards.

The bird count began in 1900, with only a few dozen observers in 25 locations. Last year, more than 71,000 people participated in 2,369 locations.

Audubon and other organizations use data collected in the count to determine the health of bird populations. If a certain species is declining, conservation measures can be implemented to help that species rebound.