Everyone knows what an eruption is. When a volcano blows its top and spews ash and lava from the cone, that’s an eruption on a grand scale. People prone to temper tantrums can erupt. So can shook up pop cans. But there is a homonym of eruption that’s not nearly as well known: irruption.
When applied to biology, irruption means a sharp increase in numbers. This term is probably most familiar to birders, many of whom eagerly anticipate irruptions of boreal songbirds.
Boreal refers to the vast belt of northern forest that covers much of Canada, Alaska, and the northernmost United States. Sometimes referred to as taiga, the sprawling boreal forest blankets over 1.5 billion acres in North America.
The boreal forest is home to several species of songbirds that specialize in feeding on the fruit of conifer (evergreen) trees, and other northern tree species such as birch.
Most boreal tree species are cyclical in their production of fruit — there are boom and bust years. It’s the bust years that create interesting birding for Ohioans. A lack of food up north can send scads of winter finches and other boreal songbirds south into Ohio, and in some years these irruptions are especially noticeable.
The fall and winter of 2012 is shaping up to be a good invasion of boreal irruptive songbirds. Leading the pack is the pine siskin. These little finches are closely related to American goldfinches, and often share space with their yellower brethren at backyard feeders.
Siskins are about the same size and shape as goldfinches, but are much browner and heavily striped with blurry brown streaks. Tinges of gold in the wings and tail are distinctive.
Pine siskins are turning up in big numbers all over Ohio, and dozens are descending on favored backyard feeding stations, especially those that stock thistle seed.
Red-breasted nuthatches have also appeared en masse. These dinky tree gleaners resemble the more familiar year-round resident white-breasted nuthatch, but are an inch shorter and weigh half as much. They also sport a bold black line through the eye and are washed with cinnamon-orange underneath.
Red-breasted nuthatches are particularly fond of suet, and slapping a cake of the fatty meat byproduct to a tree trunk may lure these interesting visitors from the North Woods.
Other possible boreal visitors to the backyard feeders include common redpoll, evening grosbeak, purple finch, and red crossbill. If you don’t already have one, get a good bird field guide so that you can better identify any strangers that appear at the feeders.
Keep those feeders stocked, too, and prepare for heftier seed bills if you are inundated by siskins or other boreal finches. Hungry packs of these feathered piglets can make mincemeat of vast quantities of seed in short order.
A short term spike in the bird feeding budget may be worth it, though — it isn’t every year that we experience these feathered invaders from the North.
By JIM McCORMA- Ohio Division of Wildlife