We observed interactions between a nesting pair of Pileated Woodpeckers (Dryocopus pileatus) and what appeared to be four pairs of Wood Ducks (Aix sponsa). Wood Ducks regularly approached and attempted to enter an active Pileated Woodpecker nest cavity that contained three fully feathered young Pileated Woodpeckers. The male Pileated Woodpecker often perched on a snag near their nest cavity to guard the entrance from Wood Ducks. Female Wood Ducks attempted to enter the Pileated Woodpecker nest cavity on at least 12 occasions and typically were intercepted by the male Pileated Woodpecker before they reached the lip of the nest cavity. On two occasions the male Pileated Woodpecker entered his nest cavity and forcibly evicted female Wood Ducks that had slipped into the cavity. These incidents suggest that large cavities in snags may be in high demand by Wood Ducks during the nesting season. Our observations suggest that some Pileated Woodpeckers may be able to resist attempts by Wood Ducks to usurp nest cavities during the breeding season.