down on both our visits. Breckenridge (op. cit.), however, doubts the importance of down as insulation for Wood Duck eggs during periods when the hen is absent. Fourth, Wood Ducks' ducklings leave the nest in response to auditory cues learned during the brooding period immediately after hatching (Gottlieb, J. Comp. Phys. Psych. 56:86-91, 1963). Similar behavior undoubtedly prompts the departure of young Tree Ducks, but this, too, remains conjectural. Nonetheless, the entire brood of both species left the nesting box, suggesting that the cues for departure may not be species-specific in cavity-nesting waterfowl. The survival value for all cavity-nesting ducklings which hatch i a host-parasite situation seems obvious. Weller (op. cit.) should be consulted for a full listing of interspeciflc egg parasitism among waterfowl, including cavity-nesting species. We ar indebte to Clarence Cottam for his review of this manuscript, and to the United States Fish and Wildlife Service and to the Caeser Kleberg Wildlife Foundation fo their financial support of the senior and junior authors, respectively, during the summer of 1967.