|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,