Other Bird Irruptions

Nature Watch
January 7, 2009

By Susan Benson,
CNHM Director of Education

If I mention a snowy owl, Harry Potter’s Hedwig might be one thought some readers may think about. For a naturalist, though, seeing any owl is a prize. Snowy owls might be one of the most spectacular species that flies south during an irruption year, when the prey population appears to decline. Boreal owls, northern hawk owls, and great gray owls move southward during some winters as well.

The boreal owl ranks as one of North America’s most wanted bird species on many birders’ lists. The challenge in finding this bird is all about location, location, location. Boreal owls prefer conifer or mixed-conifer forests in an old growth northern habitat. This bird becomes even more difficult to find since it roosts in dense spruce or balsam fir conifers, five to twenty feet high, usually on a branch next to the trunk. Boreal owls are not true migrants but are irruptive in nature, with most studies showing a four to five year irruption cycle. The year 2004 was its last irruption year, with over 300 boreal owls banded on the north shore of Lake Superior in Minnesota. Small rodents such as mice and voles make up 90-98% of its diet, with insects or small birds making up for the remaining food intake. Normally a nocturnal hunter, it will also hunt during cloudy daylight hours, sitting and waiting for its prey located mostly through its hearing.

The first and only time I have observed a northern hawk owl was in the winter of 2005 at the Ashland airport, where it was spending its days on power lines or telephone poles for days before I got my first glimpse. These birds are also nomadic, wandering south of their normal northern boreal forests, again during years of high reproduction followed by low prey availability. Hawk owls are mostly diurnal (active during daylight hours,) hunting for small mammals or birds from tree top perches. These birds have also been observed caching their prey, stashing it in tree limbs for later consumption.

In the area’s snow covered fields, perched atop a telephone pole, a great gray owl can sometimes be observed. This bird’s irruptions, also believed to be related to prey availability, are perhaps more sporadic. Some great grays can be seen in our area during any winter. In Manitoba, some individuals have migrated up to 700 kilometers, compared to only 43 kilometers in Oregon. In the recent irruption year of 2004-05, over 2,000 great grays were observed in northern Minnesota, an amazing occurrence compared to the normal winter bird count of 35 of this species. One of the world’s largest owls, this bird’s five feet wingspan is an amazing sight. Its main source of food is voles and other small rodents.
Some phenologists or birders will drive great lengths to see some of these birds. If you find you are one of them, the best viewing times for great gray or northern hawk owls appear to be first thing in the morning or late afternoon. Overcast or foggy weather makes for good viewing all day. When searching, focus on tree-tops for northern hawk owls, or about eye level in areas with lots of conifers for great grays. Quality observations of these owls can happen from your vehicle, making hiking into bogs or other areas less necessary.
Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M or on the web at www.cablemuseum.org to learn more about exhibits and programs.