Just about exactly two years ago, this column (Dec. 21, 2011) commented on an incursion of snowy owls that had reached the Vineyard and, indeed, brought these owls to most of northern states. The event was noteworthy because of the numbers of owls involved and the broad geographic range over which these arctic predators were moving south.
Surprisingly, the eastern half of the United States is once more experiencing a southward irruption of these impressive birds, with this invasion shaping up to be even more dramatic than the one in the winter of 2011-2012. Some of the owls have made it as far south as North Carolina, Tennessee, Missouri, and — astonishingly — the island of Bermuda. Multiple birds have turned up in many locations, and veteran observers seem to agree in calling this year’s invasion the most impressive they’ve witnessed.
Several factors make this winter’s irruption different. For one thing, advances in communications and record-keeping have made it significantly easier to study or assess this year’s event. While only two years have passed since the 2011 irruption, the intervening years have seen a proliferation of communication among birders on social media sites such as FaceBook. And the numbers of birders reporting their findings to online databases like www.eBird.org has skyrocketed.
These technologies existed two years ago; the difference is the degree to which they have worked their way into the mainstream of birding. A visit to the eBird site, which is operated by the National Audubon Society and the Cornell Lab of Ornithology, can take you to extensive and almost real-time analysis and mapping of snowy owl distribution, compiled from the field observations of thousands of active observers.
In addition to making it easier to track the movement of the owls, Internet communications have also helped shed light on how the owls behave. For example, while it is well known that snowy owls on their arctic breeding grounds subsist mostly on small rodents (lemmings in particular), photographers following this year’s incursion have produced documentation of much more diverse behavior by these birds.
I’ve encountered recent photos of snowy owls taking waterfowl (a common goldeneye, plucked off the surface of Lake Michigan) and other birds of prey (a northern harrier in New Brunswick). Vineyard photographer Jeffrey Bernier captured a shot of a snowy owl on the Vineyard carrying a partially eaten bird that defied firm identification but looked to me like a male merlin. Other photographers have documented the tables being turned — snowy owls, for example, under attack by peregrine falcons. These photos dramatically document the complex roles played by snowy owls.
Another interesting twist to this year’s owl invasion was the opportunity it presented for the birding community, which has been growing steadily in size and cohesiveness in recent years, to flex its muscle. Word got out that several snowy owls frequenting New York City airports had been shot by airport managers, who regarded the birds (correctly, in my view) as a hazard to aviation.
But word also spread that other airports, including Logan Airport in East Boston, have long been using non-lethal means to address the problem, catching the owls in traps and relocating them to less sensitive locations. A massive letter-writing, petition, and public relations campaign took off, coordinated to some extent by organizations like the American Birding Association but fueled mainly by grassroots outrage at the decision to kill these large birds of prey. Within days, New York airport authorities backed down and announced a switch to non-lethal control of the owls.
Finally, the fact that this year’s owl invasion follows the last one by only two years is interesting. While such irruptions are a regular feature in the natural history of the snowy owl, they are usually more widely spaced (five to seven years seems like a good, rough average). The southward movement of the birds is probably caused by a mismatch between the food supply — that is, the abundance of rodents — and the number of owls in the birds’ core range. A crash in lemming numbers or a bumper crop of young snowy owls may result in some or all of the owl population needing to move to avoid starvation.
Since their main prey species, the lemming, exhibits dramatic cycles in abundance, the snowy owl, a powerful flier capable of covering huge distances, takes the need to travel in stride. But a change in the frequency of “irruption years” would also indicate a change either in the population cycles of lemmings, or in the breeding success of snowy owls themselves. Changes like these are the kinds of things biologists predict will happen in the arctic as a result of climate change. So it will be interesting to see, over coming years and decades, whether the two-year interval between owl irruptions is just a fluke, or the first sign of a profound ecological shift.
This year, the Vineyard’s first snowies were detected (on East Beach, Chappaquiddick) at the end of November. Perhaps a half-dozen birds are here now, inhabiting beaches, dunes, farmland, and other open areas. One bird has been found fairly reliably at the Big Bridge on the Beach Road, where it has probably been hunting rats amid the jetty rocks. Irruption year or not, these massive white birds are striking critters, and this winter promises to give Vineyard observers their best chance ever at seeing one.