2017-12-14 / Nature

The Season for Winter Migration Visitors

By Charles Avenengo


Snowy owl perched on a rock and in flight. (Photos by Bob Weaver) Snowy owl perched on a rock and in flight. (Photos by Bob Weaver) Last week, local naturalist Bob Weaver photographed a pair of snowy owls at Sachuest Point National Wildlife Refuge. Two days later, University of Rhode Island Ornithological professor Peter Paton found a whopping seven snowy owls on Block Island.

Indeed, sighting maps indicate that in the first week of December, the awe-inspiring arctic visitors have been seen in hundreds of localities in the northeastern quadrant of the lower 48.

The owl’s presence is reminiscent of the winter of 2013-14, when snowy owls turned up in much of the continental United States, including one intrepid individual that found its way to Bermuda. It was also a winter when a number of snowy owls were seen at Sachuest Point, drawing thousands to view the striking visitors.

In biological parlance, these spates of snowy owl sightings are called invasions. Although only a few snowy owls are generally observed each winter, large numbers of these current proportions indicate there is a reason for the birds of prey to move south, which is for food.

In their normal range, snowy owls eat lemmings. Both the northern rodents and their predators have cyclical populations. When lemmings are scarce, snowy owls have been known to skip their breeding season. Conversely, when the prey is abundant, the owls produce large clutches of offspring.

While it is possible that a scarcity of lemmings may be the driving force for the owl invasions to more temperate regions, it has also been speculated by researchers that there may currently be more snowy owls because of a highly successful nesting season. And the reason for this is a bumper food crop of lemmings.

While generally not as dramatic as the snowy owl, other winter birds have also arrived from northern reaches.

Currently, Aquidneck Island’s ponds are teeming with waterfowl. In the past few weeks, nearly 30 species of waterfowl have been sighted on the various bodies of water and just offshore, with more arriving daily.

Similarly, great cormorants are moving in from the north, replacing the slightly smaller double crested cormorants that move south for the winter. Additionally, Bonaparte’s and Iceland gulls are being reported.

On the beaches and shorelines, most of the shorebirds have moved further south. During the winter months, only a few types of shorebirds may be encountered, notably sanderlings, purple sandpipers and more uncommonly, dunlins. Northern gannets are often seen from shore. However, the bulk of them will continue to push further south to the mid-Atlantic for the winter.

Throughout the island, the woods, hedgerows and brushy areas are filling up with returnees that have retreated from the north and will remain here throughout the winter. Backyard bird feeders witness a shift in species composition as birds like white-throated sparrows and northern juncos join the usual resident feeders.

Then there are the real fancies. Collectively called the boreal winter finches, these birds only invade our more temperate region during the cold months. Those with bird-feeding stations should be alert for the possibility of these northern visitors, like pine siskins, redpolls and crossbills. Every year is different, however, and their presence is irregular.

Ron Pittaways, an ornithologist from Ontario, produces an annual winter finch forecast. Similar to the Farmer’s Almanac, the forecast is widely circulated amongst birdwatchers as an attempt to predict an arrival of these boreal visitors. Pittaways bases his predictions on the seed crop production of various pine trees, which is the food for these finches. Unfortunately, the forecast doesn’t predict many winter finches. According to Pittaways, the cone crop was the best in over a decade, keeping the sprites wellfed and hunkered down up north.

More somberly, there is the annual late rash of local rarities. Most of these are vagrant western species that have accidentally landed in the east. Some of these vagrants are flycatchers, a group of birds that, as their name implies, rely on insects for food. While exciting finds to birdwatchers, these birds are often doomed, as the arrival of the cold heralds the disappearance of insects, and the flycatchers will eventually starve.

More optimistically, some types of birds that should be south occasionally linger here past their time. Specifically, catbirds, hermit thrushes, rufous-tailed towhees and swamp sparrows are seen through December and sometimes make it through the winter.

Finally, there is the familiar robin. While often assumed to fly south for the winter, and later to hearken the arrival of spring, many actually remain in the area for the winter. They can sometimes be observed in flocks of dozens or even hundreds, cleaning out any winter fruits on trees and shrubs.

Like last week’s first snowfall, the winter season for birds is here.

Winter Bird Roll Call

Waterfowl: Red-throated loon, common loon, horned grebe, and 25 types of ducks. Additionally, wintering goose flock occasionally harbor snow geese and vagrant species like barnacle geese and white-fronted geese.

Bird of prey: Northern harrier, short-eared and snowy owls. Occasionally, rough-legged hawks. Shorebirds: Sanderling, purple sandpiper, dunlin.

Gull-like: Bonaparte’s, Iceland and glaucous gulls, black-legged kittiwake, Northern fulmar. Alcids: black guillemot and razorbill (can be seen from shore), thick and thin-billed murres, dovekies (more common offshore), Atlantic puffins (far offshore).

Common winter land visitors: golden-crowned kinglet, yellow rumped warbler, American tree sparrow, white-throated sparrow, dark eyed-junco.

Less common winter land visitors: yellow-bellied sapsucker, horned lark, ruby-crowned kinglet, winter wren, white-crowned sparrow, snow bunting, Lapland longspur.

Exciting boreal winter finches to hope for: pine grosbeak, red crossbill, white-winged crossbill, common redpoll, hoary redpoll, evening grosbeak.

CORRECTION

In the Dec. 7 edition of NTW, in “Website of Living Species Hits Its Stride,” we inaccurately indicated that the iNaturalist website was launched in 2008 by the California Academy of Sciences. iNaturalist was actually created as a Master’s Project by students at University of California Berkeley’s School of Information in 2008, and wasn’t acquired by the California Academy of Sciences until 2014. We also claimed that submissions to iNaturalist are monitored by curators who are responsible for keeping the taxonomy up to date. In fact, all iNaturalist users may add observations, identifications, and comments to a submission. We regret these errors.

Naturalist Charles Avenengo has been chasing Aquidneck Island wildlife for more than 40 years.

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