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Competition rages among the feathered species

123rf.comA male Anna's hummingbird prepares to drive off competitors. Competition takes many forms among birds around backyard feeders.

It doesn’t take long for the first aerial battle of the day. Just as colors begin to fill in the shadows of a new dawn, the Anna’s hummingbirds are at it.

The dominant male perches protectively not far from the feeder and challenges other males attempting to take a sip of sugar water. The other males have no chance to taste the reward as a vigorous chase ensues, running the trespassers out of the yard. Within seconds the dominant male returns to resume its vigil over “his” feeder. Passing females get the same treatment. It’s a marvel the species continues. You would think males would at least treat females a bit more kindly, but no.

This is the kind of competition that makes good footage on nature shows.

“I will fight tooth and claw for the resources I need” — food, territory, mates. OK, no teeth or talons on a hummingbird, but you get the point. Ecologists call this “interference competition.”

Competition can take other more subtle forms. “Exploitation competition” involves one individual or species being more efficient at using resources. This may involve finding and consuming food faster than another individual or species.

This brings me back to the rising sun. As I conclude the morning chores of feeding the birds, taking the dog for a walk, and cleaning the kitchen a bit, I take my first sip of coffee while staring out the kitchen window into the yard. The regular host of hungry birds is already scrambling to secure breakfast.

The spotted towhees work the ground under the lilac and viburnum, scratching away to uncover sunflower seeds that may be concealed by fallen leaves. The dozen or so golden-crowned sparrows scour the ground under the dense vegetation. Then there are the dark-eyed juncos searching for the seeds that fell farther out on the lawn.

It is a tranquil scene that gives me pleasure as I plot the course of my day. However, it conceals the daily competition for resources. Do the juncos prefer to feed on the lawn, or would they prefer to feed closer to cover?

One study found that juncos feed closer to cover when sparrows are absent. It makes sense. I found evidence of three murders in my yard this fall and winter. Scattered feathers reveal the visit of a Cooper’s or sharp-shinned hawk. We have one of each in the neighborhood. Each time the victim was a junco. The towhees and sparrows, feeding closer to cover, appear to be better able to find safety.

This suggests competition to secure the best and safest foraging sites. The golden-crowned sparrows exclude the juncos from areas closer to cover. Maybe they are more efficient at gathering the food, forcing the juncos to move farther out to find a meal (exploitation competition) or maybe there is subtle aggression that excludes the juncos (interference competition). The same sort of interactions may involve the towhee in this game of survival, allowing it access to the safest of foraging spots.

Size does matter in nature. The towhee is larger than the sparrow, and the sparrow is larger than the junco. A contest of force and/or intimidation favors the larger individual.

Time for a second cup of coffee.

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