Wednesday, January 19, 2011

A Not So True Blue Jay

Everything I know I learned from helping my 5th grader with her science reports. She asked me what she should write about this week. I said I didn't know. A little while later she was peering through a microscope at a feather, the close inspection of which led to internet searches to find out what she was seeing. 

Rows of barbules, it turned out, which branch off from rows of barbs, which branch off the central rachis of the feather. It's the rows of barbules that can be pulled apart, then preened back together, their hooked ends interknitting to keep a bird in fine feather.

Our internetting also shed light on how blue jays shed light, which is to say very deceptively. Tricksters they are. The blue we see, in sky as well as in feather, is not the sort of blue that comes from pigment, but rather from the way light is scattered.

Lit from the front, a blue jay's feather shows blue--

a blue that fades as the light comes mostly from the back,
then disappears altogether when strongly backlit.

The afternoon's research ended before we could find out if the difference in color between a blue jay and the closely related crow comes not from pigment but solely from the way light bounces off their feathers.


  1. I recommend that you and your daughter take a look at the article on feathers in the current "National Geographic". It is quite spectacular.

    Bird feathers (and dinosaur feathers) can be colored both by pigments and by diffraction gratings, but blue is always due to diffraction.

    Melinda Varian

  2. Melinda also emailed me the following link to a good explanation of how bird feathers can produce color without having to manufacture pigment: