Time to buy a reference book

I need to add to my library of bird and wildlife books. While I'm good on British mammals and OK on most common avian species, my knowledge of ducks and waterfowl is not great and certainly doesn't extend to rarer ducks. I also come up short when it comes to identifying the male or the female of a particular species. So, I'm off to buy a reference book that should help plug the gaps. In the meantime, here's one of the reasons why…