Fallston. -- It was a perfect fall morning, crisp and clear. After two days of persistent drizzle, the sun was slowly rising over the wooded ridge, its shimmering rays dissecting the remnants of a predawn fog that still clung to the wooded slopes adjacent to the Little Gunpowder Falls.
I was sitting on a large outcrop of rock absorbing the spectacular autumnal panorama, mesmerized by the leaves that slowly sifted from the forest canopy to its floor. Suddenly a rustling noise coupled with a quick movement lifted me from my trance.
Without moving my body I shifted my eyes in the direction of the commotion. At first I could see nothing. I waited, carefully examining each segment of my visual field, trying to match it to a mental template of some known organism. After several long seconds, my patience was rewarded, as first one, then two fox squirrels seemed to materialize magically from the leaf litter some 60 feet away.
The distance was too great and the light too dim for me to be certain what they were doing. Slowly I raised my binoculars. To my amazement the squirrels were not alone. They were in the company of three white-footed mice, and all five were busily gnawing on the remnants of what appeared to be a white-tailed deer antler.
Although I had never before witnessed this behavior I recognized its significance immediately. The creatures in this mixed aggregation were availing themselves of an important and generally scarce mineral resource -- calcium. Here was the answer to a question that has long perplexed many central Marylanders: If antlers are shed annually, why is it so unusual to find them in habitats that are clearly overpopulated with deer?
As I watched in silence I realized how adaptive this peculiar behavior is, and I began to chuckle as I thought of other strange feeding habits exhibited by wild and domestic animals.
Almost everyone knows that seed-eating birds ingest small stones to augment the grinding capabilities of their crop. Some people may even be aware that penguins swallow pebbles for ballast, to increase diving efficiency. But how many people are familiar with perhaps the most bizarre trophic behavior of all -- coprophagy or feces eating?
Many animals are documented to eat their own digestive by-products, and by human standards this is disgusting behavior. Rodents (squirrels and mice) and lagomorphs (rabbits and hares) routinely practice coprophagy. As a child, my friends and I often came upon a mound of rabbit "pellets" in the farm fields adjacent to our Texas homes. They had been carefully deposited by their creators to mark the boundary of a territory.
To us they were a source of hilarity. A widely circulated rumor maintained that captive rabbits would routinely eat their own droppings and since this seemed "stupid," in a form of reverse adolescent logic, we jokingly referred to them as "smart pills."
Years later I learned that this behavior was not only smart, but necessary to the nutritional well being of rabbits, as well as many rodents. It turns out that these animals lack the ability to synthesize the essential vitamin, B12. As an evolutionary compensation they have symbiotic microbes in their posterior gut which produce the vitamin for them. Unfortunately, the B12 passes out of the digestive tract before it can be absorbed -- necessitating the development of coprophagic behavior.
Domestic dogs practice coprophagy too, but this behavior likely is more important in perpetuating parasitic life cycles than in reliving nutrient deprivation.
The quiet serenity of the moment was abruptly shattered as two fisherman noisily approached along the streamside trial. In an instant, the five furry opportunists scattered in as many directions. I hastily descended from my perch to examine the remnants of the gnawed antler before slowly retracing my path through the forest toward home. There I would find a hungry dog, a lonesome rake and a yard full of leaves to greet me. It would be winter before I knew it.
Don C. Forester teaches behavioral ecology at Towson State University.