The subject heading of the Mainebirding e-mail alert read “boreal owl.” I excitedly opened it but was dismayed to find this small owl had been found dead on Monhegan Island last week.

Someone on the mail list had speculated the bird had probably died of starvation. Unfortunately, for visitors such as this unusual bird, this may be all too often the case.

Boreal owls are birds of the far Canadian north and Alaska. Populations exist also in mountainous areas of the Northwest and western United States, but none are documented as breeding in the eastern U.S. Normally, they stay on or near their breeding ranges year-round. However, we may see them during winter following an intricate series of events that occur in their food chain.

As I was researching boreal owl sightings, I came upon reports related to irruptions of other northern birds, specifically songbirds. Beginning unusually early in the fall, birders had begun documenting their numbers here in the Northeast and beyond. According to a report on the Cornell Lab of Ornithology’s “eBird” Web site, birds such as the pine grosbeak, common redpoll and Bohemian waxwing were reported in New York state at record early dates. Large numbers of other birds such as red-breasted nuthatches, pine siskins and purple finches had already been reported as far south as Georgia.

Northern shrikes, also a boreal species, “have been reported in greater abundance than any other fall in the past five years,” with birds being seen “beyond the normal irruptive limits of this species,” according to the eBird report by Matthew Medler of the Boreal Songbird Initiative.

Shrikes prey upon other birds, such as the northern finches listed above, so it isn’t surprising their irruptions would mirror those of their prey. However, a boreal owl’s primary food source isn’t other birds – it is small mammals such as voles and deer mice.

Ron Pittaway, writing for the Ontario Field Ornithologists Web site, reports these small mammals were abundant this past spring and summer. Their breeding and survival successes were presumably due, he said, to a plentiful seed, berry, and nut crop observed in Canadian provinces in 2006.

Pittaway goes on to describe that cold and snowy weather of late spring 2007 froze the buds and flowers of many plants, resulting in poor crops throughout much of the north this past summer. Because these crops are heavily relied upon by both songbirds and small mammals such as mice and voles, two things can happen: the songbirds irrupt out of their normal ranges in search of more seed, berry and cone crops, while the mouse and vole populations crash. This in turn causes certain northern raptors to irrupt from their ranges, looking for sustainable populations of these mammals.

It appears part of this scenario has, in fact, taken place.

Writing on the Ontario Birds mail list, Pittaway describes the scope of the event:

“We are experiencing the biggest winter finch irruption since the ‘superflight’ of 1997-1998, when many boreal finches went well beyond their normal ranges. The cause is the largest tree seed crop failure in a decade across more than 3200 kilometers (2000 miles) of boreal forest from Saskatchewan into Quebec… boreal winter finches are being reported in many areas of southern Ontario and the United States, where some species such as pine and evening grosbeaks haven’t been seen in years. There is no telling how far south this ‘superflight’ will go.”

It’s hard to say if boreal raptors are being affected to the same extent. There have been an unusually large number of sightings of barred owls (which isn’t a strictly boreal species), as well as numerous reports of rough-legged hawks. The dead boreal owl found on Monhegan Island could be unique, or there could be others throughout the state.

If the birds are traveling beyond their normal ranges in search of prey, they are most likely severely food-stressed, as the owl on Monhegan may have been. Should you see one, care should be used to disturb it as little as possible.

You can report any unusual bird sightings by calling the Maine Bird Alert hotline at 781-2330, or by visiting www.mainebirding.net/rba/birdalert.

bdnsports@bangordailynews.net