When I first heard this term I had a vision of little birds spewing out of a volcano! But we’re not talking about that kind of eruption, we're talking irruption!
In the avian world, a bird irruption is a term scientists use to describe unusually large numbers of non-migratory northern birds that move out of their nesting range, typically in North America’s boreal forest. The birds leave the vast, wild expanse of forest, tundra and wetlands that span the width of Canada and Alaska to spend the winter farther south than normal. The irruption occurs because of changes in food supply.
The species that most commonly engage in irruption behavior are northern owls, such as the Great Gray Owl (below) and Snowy Owl (above), and certain grosbeaks including evening grosbeaks (left). In irruptive years, large numbers of these species may move down into the United States. I hope you have been lucky enough to see one.
This winter there is an irruption of snowy owls coming south into the United States and one was even spotted in Los Angeles. And this event is causing another kind of irruption—photographers and birders are swarming into these areas to photograph and view these magnificent birds.
Bird migration is a familiar and predictable seasonal movement of birds. Species that migrate do so every year at approximately the same time, traveling in a predetermined pattern, often to exactly the same destination time after time. Migrations are closely related to the breeding season and the arrival of spring in the breeding range. In contrast, irruptions are unpredictable. It’s all part of the wonderful and amazing world of birds!