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Backyard battles

Competition plays out in the skies, fields and backyards around us — even if we don’t notice it
123rf.comA black-capped chickadee perches on a redbud tree.

In the sagebrush country east of the Cascades, a Swainson’s hawk newly arriving from its winter home in South America circles above the soaring red-tailed hawk that had established its territory several weeks before.

The Swainson’s hawk dives on the red-tailed hawk repeatedly. It never strikes the redtail, but the redtail is intimidated. Both lay claim to the ground squirrels in the alfalfa field below. It is usually the Swainson’s hawks that prevail, pushing aside the redtails to somewhat less productive fields.

This is one of the more obvious cases of competition between species, but competition takes many forms. Many are more subtle. Most events pass unnoticed by people — even those tuned in to nature — as we go about our lives.

Each winter and early spring, I focus my attention on the black-capped chickadees and oak titmice in my yard. Both wait eagerly at the feeding area at first light for a somewhat tardy (in their opinion) human to replenish the sunflower seed supply for the day. The two ignore each other as each repeatedly plucks a seed from the feeder and bashes away at it against a limb to secure the kernel hidden inside.

Between early January and mid-March, the tranquil scene becomes a little more tense. Several times over the years I have watched the standoff between a pair of chickadees and a pair of titmice in a tree above a nest box. Both have their eyes on the box for the upcoming breeding season. They hurl vocal “insults” at each other. If one moves higher in the tree, the other follows. If a pair moves to the adjacent tree, the other follows. They never approach closer than six feet, but the tension is obvious. It is usually the titmice that win, and the chickadees retreat down the road to another nest box.

The “chickadee/titmouse” niche is filled by closely related species around the world from England to South Africa to China. A niche can be thought of as an ecological role filled by a species. This niche involves small birds that feed upon both insects and seeds plucked from foliage, stems, bark and even the ground in lean times. They are nonmigratory and nest most often in tree cavities. Species that share the same limited resources in the same place find themselves in competition with one another.

A field guide reveals the oak titmouse is largely a California species inhabiting oak habitat and gardens just reaching the Rogue Valley. Black-capped chickadees are a bird of the north woods mostly in riparian areas and backyards. Their range extends south from Canada to Yreka. The limited overlap in range may reflect specific habitat requirements of each, but I suspect competition plays at least a partial role in sharpening the geographic division between the two species. It seems somewhat surprising that the brief vocal duels that occur while frost is on the ground can influence the range of a species, but there are many other similar examples in nature.

Locally, you can see this same kind of ecological separation among our other chickadees. Chestnut-backed chickadees favor Douglas-fir while mountain chickadees favor true firs and Ponderosa pine. I imagine vocal duels between each.

Stewart Janes is a retired biology professor as Southern Oregon University. He can be reached at janes@sou.edu.