One of the more exciting types of avian events is a finch irruption — a large-scale movement of one or more finch species south of their usual range, usually in fall or winter, and usually in response to a deficient food supply up north, where the birds would normally be. (Birds other than finches can also irrupt; the term is used, for example, to describe a big southward movement of snowy owls or red-breasted nuthatches.)
Irrupting birds typically travel in highly mobile flocks, often descending on rich food sources such as feeding stations or commercial flower fields. The flocks can be large ones, and they seem to appear out of nowhere, and then move on just as abruptly.
The Vineyard is experiencing one of the more dramatic irruptions of recent years. The species involved is the pine siskin, a small, brown-streaked songbird with a short, deeply notched tail and a finely tipped bill. Seen well, siskins show yellowish feather edges in their wings, about the only real color to be found on this bird.
This year’s siskin irruption is unusual in both numbers and scope. By late September, reports of irrupting siskin flocks were coming from southern Canada and the northern tier of states all the way across the continent, and birds had penetrated as far south as the Gulf Coast states. The movement may have been most pronounced in the Northeast, where it was linked to a poor crop of spruce cones — a typical food source for siskins and other finches — farther north. But birds were reported emanating from regions that appeared to have normal seed supplies, suggesting (to me, anyway) that food supply isn’t the only factor involved in triggering these events.
Siskin flocks are usually rather chatty, the birds giving a thin, sibilant flight note as they travel or flit around while foraging; siskin vocalizations resemble the notes of American goldfinches, which is not surprising since the species are closely related. I often hear siskins before I see them, especially if they’re traveling at high altitude.
On the Vineyard, as far as I can tell, the first hint of the irruption came on Oct. 7, when Pete Gilmore found a single siskin at Sheriff’s Meadow Sanctuary in Edgartown. The sighting struck me as notable in part because it was early in the season for northern finches, and in part because the bird appeared during a period of strong southerly winds. That pattern suggested that the bird had traveled south of our latitude and was using the south winds to move back north.
Promptly after Pete’s first report, the siskin sluices opened. Pete and Bob Shriber encountered a flock of about 100 at Gay Head on Oct. 8. Penny Uhlendorf reported 49 at her feeders off Lambert’s Cove Road on Oct. 12; Jerry Twomey added 20 more at his bird bath and feeder on the 15th. Other Island birders reporting the species have included Timothy Rush, Lanny McDowell, Hans Goekel, Maggie Bresnahan, Susan Wilson, Sarah Carr, John Nelson, Dardanella Slavin, Debby Athearn, David Padulo . . . well, you get the picture. Pretty much everybody who notices birds has run into siskins.
My own first encounter with these wandering finches came on Oct. 11, as I was doing some field work near the beach at Long Point Wildlife Refuge. A flock of about 40 came in off the water, flew north to a clump of pitch pines, and dropped into the pine branches to rest and feed. The winds were robust from the north at the time; these birds had likely explored south of the Vineyard, taking advantage of the winds to carry them, and then reversed direction when they realized that the next stop was South Georgia Island, with a lot of water in between.
How this irruption will proceed from here is anybody’s guess. The movements of irrupting flocks are often fickle and unpredictable; indeed, “random” may be the best word, because these birds are presumably traveling over new territory with only instinct, the winds, and a view of the habitat below to guide them. Irruptions often end as abruptly as they start. Or they can persist all winter, with the first species that irrupt sometimes being joined by other species as the season progresses. (Crossbills, redpolls, and even pine grosbeaks are among the finches that exhibit this behavior. Birders will be vigilant!)
This massive push by siskins overwhelmed an earlier, more subtle irruption of red-breasted nuthatches, which have been on the move in modest numbers since mid-August. These mass migrations have added some zing to an autumn birding season that has generally been lackluster, and Island birders are hoping for more waves of seed-eating visitors from the north.