Hooded Merganser (Lophodytes cucullatus)
Growl Call: Given by males during courtship displays, most of which involve displaying their attractive heads by shaking, stretching, pumping, and twisting them. The Growl call, a descending 2-part croaking growl, is often described as amphibian like and is the source of the Hooded Merganser's colloquial name "frog duck" (Dugger 2009, Elliott and Colver 2008).
Pop Call: A loud hollow pop, is given by males during courtship displays, often just before or after the Growl Call.
Hooded Merganser Growl and Pop calls, March 26, 2011, Milwaukee River Floodplain Forest State Natural Area, Washington County, Wisconsin. The Pop calls can be heard faintly at the 6 and 10 seconds mark.
Dugger, B. D., K. M. Dugger and L. H. Fredrickson. 2009. Hooded Merganser (Lophodytes cucullatus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/098 doi:10.2173/bna.98
Elliott, Lang and Kevin Colver. 2008. The Calls of Ducks and Geese. Stackpole Books, Mechanicsburg, PA.