Since both the number and the variety of birds increase during the warmer months, one might think that rare bird sightings are also most common at that time of year. While this is often true in the Desert Southwest, where Mexican species wander into the relatively cool forests of southern Arizona, rare birds are most often spotted from late autumn to early spring throughout most of North America.
Rare loons and waterfowl such as scoters, Harlequin ducks, Barrow's goldeneyes, oldsquaws and smew often get caught up in migrant flocks of more common species as they move about in search of open water; this is also true for a variety of rare and uncommon gulls. Irruptive bird species, whose numbers vary widely from year to year, move down from the north or out from mountain corridors in concert with the availability of food and the severity of the winter weather. Among these latter birds are snowy and great gray owls, snow buntings, redpolls, crossbills, northern shrikes, Bohemian waxwings, evening grosbeaks and rosy finches. Then there are the inexplicable sightings of summer birds that failed or refused to migrate.
Many of these rare birds turn up on the Audubon Christmas Count each year but may also appear at your local reservoir or in your own backyard. Indeed, one of the joys of birding (and a major motivation for many patrons of that hobby) is the potential opportunity to find rare species amidst the usual cast of characters. While that chance may occur anywhere and anytime, your prospects increase over the next few months.
