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Long before it caught the attention of Harry Potter fans, the snowy owl already represented its own kind of magic for fans of the outdoors. This powerful white owl is emblematic of the far north, spending the summer from treeline north to the northernmost land of Canada, Scandinavia, and Siberia. Even in winter, most snowy owls in North America stay near the Arctic Circle, with only a few drifting to southern Canada and the northern United States.

At least, that's what happens in an average year. About one winter in every four, the numbers of snowy owls moving south in early winter are noticeably increased. Then the ghostly birds are spotted in dozens of locations south of the Canadian border, creating excitement among the local birders.

We had seen a , in winter 2011-2012, with owls from coast to coast and many in the interior south to Kansas and Missouri. The following winter, 2012-2013, had seen a smaller "echo" flight develop. So we assumed that numbers would be much lower this year, in a return to "normal."

We were wrong.

During the last week of November and first days of December 2013, it's become apparent that something is going on with snowy owls. Even people who pay close attention to bird records were taken by surprise because it developed so rapidly.

Along the short coastline of New Hampshire, it's not too unusual for one or two snowies to show up. This year one was found as early as November 22. But by the 30th, at least 12 were on or near the New Hampshire coast, with up to five visible from one spot. Just to the south, in Massachusetts, a few snowy owls appear every winter. This year on December 3, observers counted at least eight in the immediate Boston area, plus five visible from one spot in Salisbury, 13 visible from one vantage point in Rowley, and others at scattered sites on the coast. In Maine, compilers struggled to keep up with all the sightings of multiple birds along the coast, including several well offshore at Monhegan Island.

The birds are going south, too. Multiples are scattered around New Jersey. In Delaware, the last previous record had involved a single bird in 2005, but by the beginning of December the state had at least five, possibly seven. Two had reached Virginia. One on the Outer Banks of North Carolina provided one of very few records for that state, but then a second bird was found inland.

The numbers of snowy owls, their sudden arrival, and the southward extent of the flight all have been noteworthy. But what really stands out about this year's invasion, so far, is the fact that it is focused so far east. There have been some good counts around the eastern Great Lakes (such as eight along the Lake Erie shoreline at Cleveland, Ohio, and four at the airport at Syracuse, New York), but the majority of the birds have been found along the Atlantic Coast—or even off the coast.

Newfoundland is the easternmost part of Canada, a very large island at the mouth of the Gulf of St. Lawrence. It's not unusual for snowy owls to arrive there in winter. This year, three were found on November 15 in the Cape Race area, but their numbers increased rapidly. Bruce Mactavish and friends found 42 birds there on November 30, a number that Mactavish regarded as "staggering." But the very next day, the same group of observers scoured the same area again and counted 138 snowy owls! These were all in the general vicinity of Cape Race, at the extreme southeastern tip of Newfoundland. If an owl were to fly south from there, it wouldn't see land again until it reached Bermuda.

The island group of lies about 600 miles off the coast of the southeastern United States and 1,200 miles south of Newfoundland. With its subtropical climate, it hardly seems like habitat for snowy owls, but there have been a couple of past records. This fall, at least two and probably three have arrived there. For multiples to have reached this isolated bit of land, we can only imagine how many of the owls must be out flying over the open waters of the Atlantic.

So—why is this happening? So far, we don't have a complete explanation. The majority of the invading owls are heavily marked young birds, hatched this year, so evidently snowy owls had very good breeding success this year in the eastern Canadian Arctic. And evidently there isn't enough food in the Arctic now to sustain them, so they are moving south. But are there exceptional conditions in the Arctic right now—unusual weather, unusual lack of sea ice—that would be affecting the owls' movements? We are still working on that question.

The images to the left are from searches on , the online database of bird sightings run by the Cornell Lab of Ornithology and . They show snowy owl sightings for November only, for 2009 (a non-invasion year), 2011 (the last big invasion), and 2013. (Others are found later in the winter, of course, but these are restricted to November to allow comparison to this year.) Each marker represents a single location, but doesn't indicate anything about numbers of individuals. Notice how this year's flight is shifted sharply to the east, including observations on Newfoundland and Bermuda.

If you are lucky enough to see one of these majestic birds, please observe it from a respectful distance. Many of the snowy owls moving south are inexperienced young birds, already stressed by hunger, and it may hurt their chances of survival if they are repeatedly approached and flushed by humans. Snowy owls favor very open habitats, such as fields, dunes, and marshes, so it should be possible to get good views of them from a long distance away.