Structural colouration in feathers

Male mallard duck and its varying head colour.

Structural colouration is the delightful phenomenon of certain bird feathers where light-play and colour change occur based upon illumination and viewing angle.  I find it in the throat feathers of male hummingbirds and noticed it in the heads of male mallard ducks yesterday as I was out with my camera.

If you look closely at the birds in the above photo, you will notice that the brown chest feathers and gray back feathers have no such colour-play.  The structure of those feathers differs from the iridescent ones.  So, what is it about the iridescent feathers that make them behave the way they do?

It turns out there are five different ways in which feathers can produce this iridescent sheen (see image and link below).  In all cases the colour-play comes down to feather structure at the microscopic level, a form of nano-technology if you will.  These structures called melanosomes, "interact with light to amplify certain wavelengths depending on the viewing angle."  

Taken from:  https://environment.princeton.edu/news/birds-dazzling-iridescence-tied-to-nanoscale-tweak-of-feather-structure/

The rods and platelets present in the feather barbules reflect and absorb light at different intensities relative to the viewer.  Females tend not to have such feathers as they would make them more conspicuous in brooding and rearing situations.  Males, on the other hand, embrace the need to show off and such displays are correlated to mating success.  

Regardless of why it happens, the simple fact is that these melanosomes are beautiful to look at and are another reason why birds are such amazing creatures.  

Thanks for reading.

Eric Svendsen     www.ericspix.com