SCOTT SHALAWAY Migrants can be sporadic visitors

Cardinals, chickadees, woodpeckers, and goldfinches headline any poll of most popular feeder birds. One of the reasons for their popularity is that we see them every day. Their familiarity endears them to us.
However, one of winter's most striking visitors, the evening grosbeak, is absolutely unreliable. These on again, off again winter wanderers appear in great numbers one year, then may be totally absent the next.
A few years ago, for example, dozens of evening grosbeaks visited my feeders and gorged on sunflower seeds. The next year I saw none. The following year a few appeared. And the next year several dozen showed up in my yard in late November. Only their unpredictability is predictable.
I observed the same erratic pattern of winter occurrence when I lived in Oklahoma. Among the membership of the local Audubon society, it was always big news when grosbeaks descended on Stillwater. Maybe they'd stay for the Christmas bird count, we'd hope.
Hard to miss
In years when evening grosbeaks visit, they're hard to miss and easy to recognize. Husky, cardinal-sized yellow finches with a huge, lightly colored bill and black tail and wings, grosbeaks suggest an oversized goldfinch to some.
Males sport a bright yellow forehead and eyebrow stripe. The rest of the head is dark, and the belly and rump are bright yellow. In flight, which is distinctively undulating, black wings are set off by large white wing patches.
Females are grayish with just a hint of yellow on the belly and have white wing patches on each wing. The loud, clear call note grosbeaks give while feeding is also easy to recognize after a few encounters.
To understand why grosbeaks don't always spend their winters with us, we must understand a little about the natural history of both the birds and their food.
Evening grosbeaks live "permanently" in the coniferous forests of the Rocky Mountains, southern Canada and the northern tier of states in the midwest and northeast. Their favorite winter foods are the seeds of conifers and maples. Therein lies the explanation for their wandering ways.
The number of seeds these trees produce from year to year varies greatly. Some winters trees hang heavily with seeds; other years they're virtually bare. Typically, it's a two-year cycle.
Such an unreliable winter food supply compels evening grosbeaks (and other birds such as red-breasted nuthatches, pine siskins, purple finches and redpolls, which also depend on these unpredictable winter foods) to wander in search of food during lean years. They move south until they find seed-laden boxelders (a type of maple and a grosbeak favorite) or bird feeders stocked with sunflower seeds. And there they'll stay, roaming from yard to yard, neighborhood to neighborhood or even town to town, gorging themselves on the easy pickings provided by human benefactors.
Irruptive migrants
Ornithologists call these erratic southern movements "invasions" or "irruptions" and refer to these species as "irruptive migrants." A big invasion year is a welcome event for anyone who feeds wild birds.
Though grosbeak invasions are natural events, they are probably exaggerated by our penchant for feeding birds and planting boxelders as backyard shade trees. Over the last 100 years the grosbeak's winter range has steadily expanded east and south.
After one good look at a grosbeak, it's easy to understand why they like sunflower seeds. As the name suggests, a grosbeak's bill is enormous -- perhaps even a bit larger than a cardinal's. It's designed to crack seeds.
At feeders grosbeaks are fun to watch because they can be domineering birds. They seem to prefer open trays or tube feeders. Grosbeaks hold their place at the feeder by opening their bills and lunging at other birds that violate their "personal space." Sometimes they spend more time jousting than eating.
I'm hoping that this will be a big year for irruptive migrants. I've read reports that the northern tree seed crop is poor, and purple finches have been at my feeders since October. I've also read reports of pine siskins and red-breasted nuthatches from areas south of my location.
My advice for the winter? Keep the feeders full and binoculars at hand.
sshalaway@aol.com