The Difference - Cob and Pen

I am always being asked " How do you tell the difference between the male and female Swan ?"
At a distance it is almost impossible - however, close up there are a number of differences. The main difference can be seen in the photo I prepared, showing Penny on the left and Duke on the right.

The large black fleshy lump at the base of the bill is much larger and more pronounced on Duke, this can be called the "berry". Seen close together, Duke is slightly larger with neck slightly longer and thicker. 

His tail is also wider and more fanned out, whereas Penny's comes to a single point. There are other differences such as leg skin colour, and variations where the black flesh meets the bill, all these observed over a period of time gives me a more detailed knowledge than most.