This image of a northern pygmy owl calling to its mate from a woodpecker hole in a quaking aspen tree took just a fraction of a second to make.

For wildlife photographer Paul Bannick, however, it took days of careful tracking, observation of avian behavior and infinite patience to capture the moment. After traipsing through the still-snowy woods last spring in the south-central Washington Cascades, he heard an owl call, so he gave a response. Then a second owl joined in.

"After that, I listened and watched, not wanting to disturb the couple," he recalls.

After observing the pair for a few days, Bannick saw a fist-size female fly into a hole made by a hairy woodpecker, indicating acceptance of the cavity as a new nest...