A chorus of music from the trees, a flash of color in the sky.

You may not always notice them, but surely would miss them if they were gone.

The birds that live in our forests, cities and neighborhoods remain the most visible remnants of the area’s wildlife that civilization largely has overwhelmed.

Yet unlike other wild creatures, birds have adapted to life among humans, pecking away at seeds in backyard feeders, nesting in birdhouses and splashing in birdbaths.

Knowing how many birds live among us and what species are thriving — and which are not — is key data to those who monitor avian populations. This weekend’s Great Backyard Bird Count is both a fun way to get involved in bird watching and also an important tool to help gauge the effect of ecological changes on bird species.

"Birds are probably one of the most important indicator species out there," said Peter Gordon, education director at Elachee Nature Science Center. "They give us a good idea of the ‘barometric pressure’ of the environment. We can see if their populations are dwindling, increasing, spreading, and determine the what-fors, the what-ifs and the whys."

The event runs Friday through Monday and turns amateur bird watchers into official counters in an annual census. All you need to take part is an outdoor locale that draws birds, perhaps a good pair of binoculars, and few minutes to fill out a Web-based form on the birds you see.

Those lists help researchers at the Cornell Lab of Ornithology, the National Audubon Society and Bird Studies Canada, co-sponsors of the Backyard Bird Count, learn about bird numbers and trends.

"It’s a yearly event and something that’s easy for people to do," said Kate Mowbray, a naturalist with the Sandy Creek Nature Center near Athens. "The way it’s set up, you get a lot more participants, which increases the amount of data. From that baseline of information from year to year, you can see the changes over time."

Those wishing to take part can spend as little as 15 minutes or a good portion of their day logging birds.

"Why it’s so successful is that it’s so darn fun to participate," Gordon said. "It’s science-based, but it’s also a lot of fun."

Last year, participants turned in more than 94,000 checklists, most of them online, tracking more than 11 million birds of 620 species. Georgians filed more than 3,700 checklists, eighth in the nation. And the Gainesville area ranked sixth in Georgia with 107 checklists.

"We have a lot of birders in this town," Gordon said "It’s a pretty cool area in the topography, with the lake and green spaces, and a lot of people who feed birds have nice habitats.

"When people know about it, they don’t have to spend all day because it fits their schedule," Mowbray said. "Once they do that, they think ’that was really cool’ and they want to continue watching birds in their own yard or go out on hikes at the nature center."

Watchers are asked to note the different species of birds and their number, so a guide book to identify species is helpful. Other sources are available at the GBBC Web site, www.birdsource.org, which offers maps and charts showing reports from each state and city.

Participants also may enter the GBBC photo contest; many photos are featured in a Web gallery, and participants are entered in a prize drawing.

Those who want to get started early on the count can join Gordon with a group of birders for a trail walk at 8 a.m. Friday at Chicopee Lake.

"It’s a great way to start folks off in birding and get them motivated," Gordon said. "It’s citizen science at its best."