Shedding light on a Shelduck

The wing of this freshly dead shelduck I found on the shore looks unremarkable. Until, that is, you shed some light on it from the right angle and watch as it is transformed into the most beautiful of structures.

The colour is not really there in the feathers.  Its all down to physics apparently - an illusion created by the effect the fine structure of the feather has on light that hits it at the right angle.  The shiny barbs act like miniature mirrors that reflect light and tiny prisms that split it into its component rainbow colours - some of which get absorbed and some reflected back.  Ducks in particular have this effect on the upper surfaces of the secondary wing feathers producing a specific coloured panel - the speculum. Why particularly there, I've no idea, but it certainly contributes greatly to the beauty and appeal of ducks.  Now who was it again that said, 'From the troubles of the world I turn to ducks'?  Sensible person whoever it was....