The sun had not been gone more than 15 minutes when the sound of an owl came booming out of the twilight. It was expected. We're entering owl season. This is when owls reclaim the night.

From early spring on, all through summer and the first part of autumn, other sounds made by other creatures filled dusk and darkness. But nearly all of those sounds have been silenced now by the chilled air and the shift in seasons. By the time that frost approaches, the other night criers -- things such as frogs and toads, woodcocks and whippoorwills, crickets and katydids -- all have retreated to safe shelters, flown to warmer climates, or simply perished, their work completed for the year.

The owls remain. Several species live in our region or pass through here. Most common, and certainly most commonly heard, are the great horned owls, the barred owls, and the little screech owls. No, theirs are not the only voices in autumn nights -- coyotes may howl, foxes may bark -- but when frost settles over the fields and moonlight floods the forests, it is the owls that tell us where we stand in the march of seasons. They had been biding their time for months; now they are back on center stage.

Owls call for the same reasons most songbirds sing or twitter. They are establishing hunting territories and communicating with one another, perhaps courting, advertising for mates. And they may call just because a brisk, starry night is as stimulating to an owl as a sunny May morning is to an oriole, and the owl needs to tell the world about such a night.

Both the great horned owl and the barred owl hoot, but do so in distinctly different styles. The great horned owl, named for tufts of head feathers that resemble horns, has a deep, gruff voice and usually gives a short series of hoo or hoo-hoo calls. The sounds can seem low and muffled, or they can boom through the night. Always, though, the great horned owl's voice carries an aura of wildness. This owl is a fierce hunter, and any night that includes a great horned owl immediately becomes as exhilarating to a human listener as it is terrifying to a trembling rabbit.

Barred owls are probably heard a little more often than the horned owls. Barreds even call during the day occasionally. They have a greater repertoire, too. Barred owls are known for the series of hoots usually interpreted as who, who cooks for you . . . who cooks for you all, but they also scream and wail and whistle and throw in other sounds that are hard to describe. While the who cooks for you hoots are familiar and welcome, the other sounds are weird enough to be chills-up-the-spine intimidating when they suddenly break through the darkness.

Barred owls are named for the dark lines that run across their bodies. They are nearly as big as the horned owls but are not considered on the same level as predators. They generally haunt the damper places -- swamps, rivers, low woods -- and leave the upland forests to the horned owls. Not many creatures will stand up to a great horned owl.

The screech owl is poorly named. Its call is more like a tremulous whinny or quivering wail than a screech. It's a sound that can be eerie to those not familiar with it, but the screech owl is not a scary bird, unless it is defending a nest; then it's a fighter. This owl is very small, no larger than a blue jay, and hunts mostly small rodents.

There is one owl even smaller than the screech owl that may be found in southern New England, especially now, during migration season. This one, the saw-whet -- its call sounds like a saw being sharpened on an old-fashioned whetstone -- is smaller than a robin. With an oversized head and huge eyes, it looks like a child's toy rather than an actual predator. A few nest in our area but not many people ever see or hear a saw-whet

More visible is the short-eared owl, which comes here in winter and hunts over marshes and fields in late afternoon and at dusk. There is also a long-eared owl, an even rarer wintertime visitor. In both species, the "ears" are like the horns of the great horned owl, merely feather tufts. We also have a few of the light-colored, ghostly, barn owls still around -- not as many as years ago, unfortunately -- and once in a while, in winter, the white snowy owls of the far north drift down our way, especially in years when rodent-hunting is poor on the Arctic tundra.

For most of us, however, any owls we hear or see will be the horned, the barred, or the screech owls. Some people may hear the hoots or whistles from their yards, maybe when coming home at night. Others have to make an effort, perhaps go out and walk a country road after sunset, to hear them. Either way, the owls are worth listening to, worth a pause.

Owls are the spirit of the late-autumn and winter night. They emphasize that some primal, untamable creatures still exist out there in the cold darkness. That is good to remember, even as we bundle deeper into our jackets with sudden shivers that have nothing to do with the frosty air.

Ken Weber, whose column appears here weekly, writes books on nature and outdoor recreation. He can be reached by e-mail at kweber@projo.com.