Tundra Swan (Cygnus columbianus)
Flock calls: A hooting hoh on several different pitches. A flock flying by at dusk reminds some people of a distant pack of hounds or flying monkeys.
Tundra Swan, flock of 25 flying past at dusk, December 4, 2011. Kettle Moraine State Forest, Waukesha County, Wisconsin.