Birders paid even more attention to their backyard feeders and on outings this winter as they encountered an influx of uncommon species. The influx is called an "irruption," and it usually happens when birds are pushed past the normal boundaries of their traditional range in search of food.

"We are always looking for weather conditions, a population fluctuation or a food shortage that will put something new on the scene," said Jack Rensel, an avid birder and retired wildlife biologist from Ogden.

One of the most popular irruptions for Utah birders is the colorful Bohemian waxwing.

"They change from an insect feeder into a fruit feeder in the winter. If they run out of food they just keep moving south until they find a source," Rensel said. "Sometimes we go three or four years without them showing up. It is always exciting when they do."

Some Bohemian waxwings showed up in northern Utah this winter, but there was not a huge influx.

Bill Fenimore, who writes the weekly Bird Sighting feature for The Salt Lake Tribune's outdoors section, says most of the irruptions in Utah come from the boreal forest region of Alaska and Canada.

Fenimore reports that northern shrikes showed up in greater numbers during the 2007-08 winter and that boreal owls were spotted in northern Utah. There were also spottings of red-breasted and white-breasted nuthatches.

Steller's jays showed up in Wasatch Front backyards this winter in increased numbers.

"During the last 22 years, I have only had a Steller's jay in my yard during three winters," said Fenimore. "Interestingly, those irruptions all occurred within the last seven years. Some ornithologists wonder if global warming/climate changes are one of the stimuli for an irruption."

Irruptions are a winter phenomenon, with the wandering birds returning to their traditional breeding grounds in the spring.