|Thanks for your comments Rick,
I checked out your sites and see your concerns. I can tell you that when they took off the did have a noise similar to a morning dove as it flys away. I figured that must be the reason they called them Whistling Swans.
I also searched Google images and typed in Whistling Swans and there was one image that looked exactly like mine, including the staining on the necks.
Thanks Rick for your interest,
Whistling Swans (10)