Identifying the two large sawbills, Goosander and Red-breasted Merganser, can be pretty straightforward when confronted with male birds. However, separating the females - or redheads, as they are more often called - can be much more difficult, especially when you throw a redhead Smew into the mix. 

This video gives useful pointers on how to confidently tell them apart, and some tips on identifying their rarer cousin, the Smew.