With the continuing frigid temperatures and mounds of snow, our backyard bird feeders have been hopping with activity.

But as the number of birds at the feeder increases, the frenzy also seems to be attracting the attention of hungry visitors that prefer their food warm.

We are talking about predators. While the deep snows have kept the neighborhood cats indoors and away from the feeders, those same cold and snowy conditions have increased the food requirements of our local Cooper’s hawk. Other winter backyard bird feeders in Maine may be visited by the smaller bit closely related sharp-shinned hawk, or even a merlin, a small, dark, tough, sharp-winged falcon. All three species are among a set of hawks that specialize in eating other birds. At backyard feeders, their preferred method is to swoop in unexpectedly to try to catch a bird before it has a chance to flee.

The other day we glanced out the window toward our feeders and were surprised at the lack of activity at the feeders. Then we noticed a black-capped chickadee sitting completely motionless in the lilac bush. Behind it, farther back in the tangle, was another one as still as a statue. The two stayed like that for more than five minutes, and we realized that a hawk had to be in the vicinity. Staying absolutely still was, for those two birds, probably a matter of life or death!

When a hawk is flying overhead and thus less of a direct threat, you will often hear black-capped chickadees give a high-pitched series of insistent alarm notes that are unlike their normal calls. Once you learn the sound yourself, you can scan the sky when you hear it, and more often than not, you’ll see a hawk flying overhead. Obviously that call is a way of alerting others in the flock to keep their eyes to the sky so they won’t get caught in a surprise attack. Occasionally, we have heard a chickadee give the alarm call and looked up to see a crow passing over. Maybe even chickadees are not perfect in bird identification!

Although forming large groups, as happens at bird-feeding stations, can attract the attention of predators, some birds (and other animals) travel in groups as a way to decrease their chances of getting eaten by a predator. The more eyes that are watching for predators, the better for getting a quick alert to allow a get-away. A predator diving into a large flock can easily get confused by the rush of escaping birds and find it difficult to focus on a single bird so that the whole flock gets away in the flurry.

Some flocking birds take anti-predator efforts up a notch. American crows, upon discovering a hawk or owl, call loudly while sitting just out of reach of the predator, sometimes diving down toward the unlucky bird’s head. If the hawk or owl flies off, the crows will follow in pursuit until the bird gets far enough away that they don’t seem to worry about its sneaking up on them. Although usually this works pretty well for the crows, we have read stories of the occasional cheeky crow that got too daring while mobbing a great horned owl and was grabbed by the deadly, unescapable talons of one of these ”tigers of the air.”

So during these busy feeder days, be sure to keep your eye out for the birds eyed by — and eyeing — the unexpected guest.

P.S. The Great Backyard Bird Count begins this Friday, Feb. 13 and runs through Monday. Be sure to count for the birds! www.gbbc.birdcount.org.

Dr. Jeff Wells is the senior scientist for the Boreal Songbird Initiative. During his time at the famed Cornell Lab of Ornithology and as the Audubon Society's national bird conservation director, Dr. Wells earned a reputation as one of the nation's leading bird experts and conservation biologists. Jeff's grandfather, the late John Chase, was a columnist for the Boothbay Register for many years. Allison Childs Wells, formerly of the Cornell Lab of Ornithology, is a widely published natural history writer and a senior director at the Natural Resources Council of Maine. Together, they have been writing and teaching people about birds for decades. The Maine natives are authors of the highly acclaimed book, “Maine's Favorite Birds.”