Edge Effect

by Dave Hanks

This is a principle that I taught in my High School Ecology classes. Where two communities meet is an edge (i.e. Sage brush ends and pine begins). There are always more numbers and greater varieties of species along an edge than deep within either community. This is because species from both communities are along the edge and there is a greater variety of factors that can either provide food or cover for the animal. Mule Deer are a good example. They can hide in the trees during daylight hours, but come out into the meadow at twilight time. The meadow furnishes feed but the trees are close enough to dash back into in case of danger. Fishermen take advantage of this principle when fishing where slow, deep water is off to the side of rapids, or along a log that has fallen into the creek. There are many types of edges.

One of the best edge effects we have experienced is in central Oregon at a place called Cabin Lake. Why it is called that I don’t know because there is neither a cabin nor a lake there. What is there is a spot where the Sage, Rabbitbrush, and Bitterbrush “peters out” and a Ponderosa Pine forest is starting with widely scattered trees. Sitting in a blind by a watering spot there has yielded more photography opportunities than about anyplace we’ve been. We were lured there because we read that it was a great place to see Pinyon Jays.

We discovered a wonderful spot. Not only were Pinyon Jay abundant, but a total of 33 bird and 5 mammal species came to that watering spot. A half dozen jay species, 5 woodpecker species, 2 bluebird and 2 towhee species, as well as crossbills, nuthatches, and chickadees to name a few. Some of the woodpeckers (like White-Headed, Lewis, and Williamson’s Sapsucker) are ones that are hard to come by in favorable photographic situations.

It is a hard, out of the way, place to find. But since that original trip, we have been back several times. The effort to get there is always rewarding because the variety is amazing!

(White-Headed Woodpecker at Cabin Lake)