NASHVILLE — It was 18 degrees in Nashville on Jan. 30, the day I made up my mind to participate this year in the Great Backyard Bird Count, which runs Feb. 15-18. By the time I got around to signing up, it was 70 degrees outside and raining torrentially, breaking a rainfall record that had stood since 1884. Tornado sirens were wailing for hours, setting back all my efforts to rehabilitate our traumatized little rescue dog by what I’m guessing will be weeks.

But right now I’m more concerned about the birds. North American birds evolved to withstand normal North American weather, and normal North American weather includes cold snaps, blizzards, floods and tornadoes. But tornadoes in February are not normal, even in the American South, and a truly severe cold snap can be devastating.

It’s too early to say what effect this year’s polar vortex and extreme flooding have had on bird populations, but in January 1977 an ongoing survey of the bird population in southern Illinois inadvertently became a case study in avian survival rates during brutal weather. Researchers conducting a bird census in the area were forced by heavy snowfall and extreme cold to stop collecting data. What they found when they were able to resume the count nearly a month later was astonishing: Whole species of birds had simply disappeared from the survey area. Carolina wrens, gone. Eastern bluebirds, gone. Hermit thrushes, gone. Two different species of kinglets, gone. Many other species were decimated, with populations reduced by up to 80 percent.

The Great Backyard Bird Count, a citizen-science project of the Cornell Lab of Ornithology and the National Audubon Society, relies on thousands of volunteers around the world to report the number of birds they see during the annual four-day event. It’s easy to participate, requiring very little time and no special expertise, though I’ve never paid much attention to the program before now. I love birds, but I’m not a real birder. I don’t keep a life list of the species I’ve encountered, and I can never tell the difference between a Cooper’s hawk and a sharp-shinned hawk without looking them up.