PINE SISKIN—INVASIVE NATIVE

The winter of 2012-2013 has seen record number of Pine Siskins (Spinus pinus) in the Pacific Northwest. Numbers in the thousands have been reported on some Christmas Bird Counts. What's going on? It turns out that siskins are cyclic, on the average peaking in a given area in alternate years, and the peaks on occasion are very high. Thus they have a two-year cycle. The cause of this cycle is usually thought to be food availability, which varies in both space and time.

Siskins are among our smallest birds. They are members of the finch family Fringillidae, a family of interest because of its adaptive radiation into the seed-eating niche. The biggest species eat large seeds, the smallest very small seeds, and so forth. Pine Siskins eat a great variety of seeds of weedy herbaceous plants in the summer, but in winter in the Pacific Northwest they are strongly associated with red alders (Alnus rubra).

Alders bear their seeds in small conelike structures, and the slender bill of the siskin is well adapted to extract these seeds. Flocks of siskins visit alder trees and spend quite a bit of time working through the abundant cones. These flocks can be of surprising large size, up to and over 100 birds, but are usually smaller.

Pine Siskins also eat a variety of other seeds, from dandelions to hemlocks, and are frequent visitors to bird feeders, especially preferring thistle seeds. Unfortunately, this can be their undoing, as they seem very subject to infection from salmonella, which is spread in their feces. Birds may defecate while at feeders, and thus the salmonella bacteria are spread from bird to bird. Most winters, people who feed birds report sick and dead siskins at their feeders, sometimes dying right on a feeder.

Pine Siskins are very aggressive little birds. Perhaps they have to be because they go around in flocks, and a bird has to defend its feeding site against others. But they are also aggressive toward any other species, and at feeders, it is an impressive sight to see a siskin chase away a larger finch or sparrow. Siskins often have yellow in the wing and tail, and larger yellow patches may enhance a bird's success in driving away others.

Dennis Paulson

SNOWY OWL FLIGHT YEAR

The winter of 2011-2012 will go down in history as a time when arctic-breeding Snowy Owls (Bubo scandiacus) came down in great numbers to southern Canada and the northern United States. This happens at irregular intervals, and this time it has been six years since the last flight year in the Pacific Northwest.

These flights are called irruptions, a word meaning 'into an area' just as eruptions means 'out of an area.' The latter is used for volcanoes, the former for unusually large flights of birds or movements of other animals, usually detected where they arrive. In this case, our baseline is no more than a few birds observed each winter, whereas the irruptions involve dozens to hundreds of birds.

Snowy Owls have been reported from many localities since November, some of them birds that were seen for only a day or two, others birds that arrived and stayed put. Numbers inland are generally small, not much higher than in non-flight years, but the majority of birds are congregated near the coast.

Up to a dozen birds have been present on Damon Point, a spit on the north shore of the entrance to Grays Harbor, and these are the birds featured here. Even more are present along Boundary Bay in southern British Columbia. At both of these localities, numerous birds can be seen from the same spot, sometimes several perched together on a log. They seem not at all aggressive to one another. In addition, a few birds have taken up residence at Port Susan Bay and the Nisqually Flats.

There is still some confusion about exactly why the owls come down in numbers only at intervals. Earlier thoughts were that they did so after a lemming population crash, the absence of their primary food sending them south. But this has never been entirely satisfactory, because lemming population cycles in different regions are independent of one another, yet the irrupting owls appear over a very wide area.

An alternative gaining more credence is that during years of lemming population highs, the owls do very well, and so many young are produced that densities in the fall are higher than normal, and this sends many birds southward or perhaps in all directions. Thus our numbers are because of lemming booms, not lemming busts.

Lemmings are absent from this area, but voles are locally abundant, and some of the birds that make these flights may subsist on these lemming relatives.

In lieu of these rodents, many owls switch to a water-bird diet, which is why coastal areas are favored. Water birds usually roost right out in the open, either on shore or on the water, and if the owls go out at dusk to hunt them, their prey is at a great disadvantage. A white owl approaching in low light levels may be just about impossible to see against a paler sky. We still don't know if they continue to hunt through the night, but they clearly don't during the day, which is why we rarely see them doing anything but turning their heads and occasional preening.

Studies based on the collection of regurgitated pellets find these coastal owls eating shorebirds (Dunlins, Sanderlings, Red Phalaropes) and diving birds (Horned Grebes, Buffleheads) as well as Black Rats that live among jetty rocks. After the breeding season, some female owls fly out to the pack ice and presumably have nothing to eat but water birds.

One last thought. These owls are magnificent additions to the local scene whenever they favor us by their presence. Although they seem tame and placid, it's always best to avoid getting too close. Each owl has its own flight distance, and observers and photographers should be sensitive to that.

Dennis Paulson