The 26th annual Great Backyard Bird Count – in which bird and nature lovers around the world unite in an effort to tally as many species as possible over four days – begins Feb. 17 and runs through Feb. 20.

Combined with other bird counts, Great Backyard Bird Count results help create a clearer picture of how birds are faring – whether individual species are declining, increasing or holding steady in the face of habitat loss, climate change and other threats.

“Based on the recently released State of the Birds report, we know that half the bird species in the United States and Canada are decreasing,” said David Bonter, co-director of the Center for Engagement in Science and Nature at the Cornell Lab of Ornithology. “We absolutely need the eyes and ears of birdwatchers to give us the big picture when it comes to shifting bird populations.”

Each participant or group counts birds for any length of time (but for at least 15 minutes) and enters the birds they identified at each site they visited, whether that is from home, at a local park or in a wilderness area. Those new to the event should read the How to Participate instructions on the event website.

People of all ages and skill levels are welcome. An estimated 385,000 people participated in last year’s count and reported more than 7,000 species from 192 countries.

The Great Backyard Bird Count website has tools and information to help both new and longtime birdwatchers. A free live-streamed webinar, Feb. 15 at 1 p.m, will provide more information about how to participate.

The Great Backyard Bird Count is a joint project of the Cornell Lab of Ornithology, the National Audubon Society and Birds Canada.

Pat Leonard is a writer for the Cornell Lab of Ornithology.