Don’t ask me! I was happily photographing a pair diving ducks feeding on the River Nairn near the footbridge in town and telling people they were a pair of Goosander! I even said that we are more likely to see them out at sea and mainly in the summer! I am so used to seeing Goosander here in the winter that I didn’t question my assumptions (always a dangerous trait; in any aspect of life!).The easiest way to tell the difference is the bill: the Goosander drops at the end, a bit like a hook at the tip, whilst the Merganser slightly tends upwards toward the tip. Otherwise, it is really tricky to tell the difference, the female particularly. With her you have to check the neck; she has a clear border between the brown and whitish grey.
The male Goosander has more white plumage on the breast and stomach (see photo below). The Merganser head is smaller and the crest more obvious (see the crest in the photos above).
Whatever mistakes I make in identifying them, it was great watching them dive. The photo below captures the moment the male stretches its head out prior to diving under water.