We all have friends who are never late for any engagement and others who are easily distracted and take a less direct approach to life. So it is with birds.
Each year golden-crowned sparrows arrive in my yard from Canada and Alaska on the same calendar date, plus or minus two days. The same is true for their departure in spring. Other birds are nearly as predictable, including hermit warblers breeding in our forests and American wigeon wintering on our farm ponds. You can almost set your watch, OK, your calendar by the movements of many birds.
A little less predictable are robins and waxwings. In a year with abundant madrone berries, they stay with us in the thousands. If the berry crop fails, most are quick to head for distant places with better fare. However, come spring there will always be a pair of robins in my yard and cedar waxwings nesting along Bear Creek.
For the epitome of fickleness, think finches. This family includes pine siskins, goldfinches, crossbills, evening grosbeaks and purple finches. I've given up predicting the movements of these birds. One spring pine siskins are everywhere in the forest feasting on madrone flowers. Then they'll vanish for years with only a few scattered individuals to be found. Early ornithologists wrote of the curious absence of red crossbills in the Siskiyous. They needed only to be patient. Some years they can be found throughout.
Then there are evening grosbeaks. In May, they sometimes drop into the valley for a visit by the hundreds to feast. In other years, they are absent. This past spring small numbers stayed to breed locally in the mountain forests, a first in my experience.
Goldfinches, too, can be erratic, but not to the same degree as their relatives. They are predictable breeders, but flocks often surge through the valley in the fall and winter. When and where? It's anyone's guess. Only the house finch in this family of wanderers seems to be predictable, which is every day at my feeder.
Why are members of this family so erratic? It starts with their food supply. Siskins tend to follow the cone crop, especially hemlock, and crossbills appear wherever pines and spruce are producing abundant cones.
Cone production depends upon growing conditions, meaning the weather, and we all know how predictable that is. Crossbills are so closely tied to their food supply that they will even breed in the snows of winter if the cone crop is plentiful.
This last observation helps provide the rest of the answer to our question. Finches and their close relatives feed their young partially digested seeds. This is unusual among songbirds.
Others that feed on seeds much of the year, such as sparrows, juncos, towhees, buntings and black-headed grosbeaks, all feed their young protein-rich insects instead. It looks odd to see a black-headed grosbeak with its massive bill collecting caterpillars, but the diet produces strong young. Believe it or not, insect populations are more predictable than cone crops and, consequently, so are the movements of sparrows, juncos and other birds that eat them.
So what will it be this winter? Will pine siskins be abundant or absent? Will next spring bring feeders teeming with evening grosbeaks? Has anyone checked the cone crop lately?
Stewart Janes is a Biology professor at Southern Oregon University. He can be reached at email@example.com.