Use your camera’s exposure compensation feature (try +1 or +1 2/3) to let more light into your picture. Take a test shot and check out your histogram. If the right-most end spikes up along the left edge, decrease your exposure compensation until the line disappears.
Adapted from The Betterphoto Guide to Digital Nature Photography by Jim Miotke. (Watson-Guptill Publications, 2007; $25)