wgeoff

The beak has a well-used look about it.

Given the quality of these digiscoped photos, I think beaks (and legs) would make an interesting subject.
The colour of this bird's beak should change to orange if it moves into breeding plumage. How does the colour change? From the bottom up, or does it all change in one go?
How does a bird change its beak colour anyway - what's the physical process?