Some winters there will be an influx of northern bird species into the southeastern United States. Here in the Smokies region of Western North Carolina, the likely candidates are various hawks and owls as well as evening grosbeaks, purple finches, red and white-winged crossbills, and pine siskins.
Ornithologists call these irregular movements “irruptions.” John C. Kricher describes the phenomenon in A Field Guide to Eastern Forests of North America (1988): “These dramatic mass movements ... are unusual both because they involve large numbers of birds and because, unlike migration, they are not generally predictable ... There is no local indication that an irruption will occur ... The appearance of irruptive species is called a ‘flight year’ ... thought to be caused by periodic unpredictable food shortages in the breeding ranges of these species. Seed-eating species may irrupt in years following the cessation of masting. Many young are produced when seeds abound during masting, producing an over-population. When the seed crops drop precipitously, seed-dependent species ... are forced southward. Not all individuals of the irruptive species leave the nesting areas, however. Irruptive flocks tend to be comprised predominantly of young birds. Of adults, females seem to outnumber males, although data are not well established on this point.”
Bird species like hawks and owls would be driven southward when there is a shortage of voles and other rodents or small mammals upon which they are dependent for food.
The evening grosbeak is perhaps the most spectacular of the irruptive species, but I haven’t seen one in years. The white-winged crossbill is perhaps the most rare of the irruptives species in our area. I last saw white-winged crossbills along the road to our house near Bryson City back in 1979. They were attracted to the salt on the pavement that the DOT had spread to prevent icing. As a matter of fact, that was also the first time and the last time I have ever seen white-winged crossbills — and since I was in a moving vehicle at the time makes the sighting questionable at best. But it’s staying on my lifelist.
I know, for sure, the siskins are here this winter in great numbers. Your best shot at seeing one (or maybe a hundred) is mixed in with a flock of American goldfinches.
In winter plumages, the goldfinches have unstreaked brownish backs and unstreaked drab-grayish undersides. The male displays some yellow about its face and throat. Both male and female will have very apparent paired white wing-bars and some white on the rump. Their tails are not deeply notched. The call is a high thin wiry “toweeoweeee.”
In winter plumages, siskins are brownish and heavily streaked overall. The yellowish wing-bars are not particularly apparent. Some field guides (like “Sibley’s”) show the female in winter plumage with an upper stripe that’s white. Other field guides don’t show any white; or if they do, there’s no suggestion that it’s a reliable indicator of sex. I haven’t made up my mind about that as yet. The tails of both sexes are deeply notched. The call is a loud “clee-ip.” If you live an urban-suburban area, the only other bird you might mistake for a siskin is the house finch.
Only in recent years have siskins extended their breeding range into the southern mountains. Until, say, the late 1980s, they were seen here occasionally during the summer months and there was no doubt sporadic breeding. The first nest wasn’t discovered until not many years ago.
Pine siskins are erratic. They nest here and there … they appear in droves or not at all … startled while feeding, they dart away like a mouse with wings before settling into an undulating fight pattern similar to that of the goldfinch.
“Presumably this pattern is related in some way to annual variation in the distribution and abundance of seeds that make up the bulk of its diet,” Dawson noted. “Reproductive schedule and attachment to a particular breeding area appear to be less rigidly fixed in the pine siskin than in many other songbirds. In some cases, members of an irruptive population may linger on a favorable wintering ground long enough to breed.”
Most people have never seen a siskin — or they saw one and thought it was a goldfinch or a really fast house sparrow. Now’s your chance ... check out your feeders and see if they’re there. If so, let me hear about it.