2 Guys walking down the street.
One walks into a bar, the other ducks.
Interesting Fact: The female chooses the nest site, and may start scouting for next year’s tree cavity at the end of each breeding season. Nest cavities can be in live or dead trees and are usually close to water. Cavities are typically 10–50 feet off the ground, up to about 90 feet. Hooded Mergansers nest readily in boxes, preferring those with wood shavings or nest material from previous uses. They prefer cavities with 3–5 inch openings.