Prince William Conservation Alliance

In Winter, Life in a Stream Gets Going

by Cliff Fairweather, Audubon Naturalist Society

The signs of approaching winter are everywhere. Trees are shedding their leaves, the last wildflowers are fading, and ground hogs, snakes, turtles, and lizards have mostly disappeared from sight. Much of nature is shutting down for the season.

In our streams, however, the partyís just getting started! Yes, thatís right, the pace is picking up under the waters of Prince William County streams.

I know this doesnít seem to make a lot of sense at first. After all, what could be less inviting in the dead of winter than the cold waters of a creek? But for many stream creatures, that creek is a great place to pass the season.

Why? Well, first of all, most stream creatures are cold blooded. Their body temperature is determined by the temperature of the surrounding water (or air). Many stream creatures are immature insects, like mayflies or black flies, that will leave the stream as adults.

I donít know about you, but if I were cold-blooded and had to choose between the waters of a creek and the outside air in winter, Iíd take my chances with the creek. After all, the water wonít get below freezing, but the outside air can get a whole lot colder than that.

Another good reason to stay in the stream over winter is the food. A pile of dead leaves marinated by fungi and bacteria might not make your mouth water, but this is just what many stream creatures eat. They get their biggest helpings of this meal when the trees loose their leaves in autumn.

Whatís good for the leaf-eaters is good for the leaf-eater eaters too. A host of predators, such as hellgrammites, dragonfly larvae, salamanders, and fish feast on the leaf-eaters (and each other).

Some members of one group of stream insects, called stoneflies, actually leave the cold comfort of the creek in winter to become land-dwelling adults. They withstand the often sub-freezing temperatures by producing their own anti-freeze! Watch for their small, dark forms on sunny winter days as they walk on the bark of trees along some of our healthier streams.

Many stream dwellers are actually better adapted to cold water than they are to warm water. This means they are vulnerable to increases in water temperature caused by storm-water runoff or the removal of shade-giving trees along stream banks.

If you have a stream on your property, you can help by planting or keeping trees along the stream. Not only do they provide shade, but their roots help protect the banks from erosion and their leaves will provide a winter feast for stream creatures.

Prince William Conservation Alliance