Feather patterns

A rather old publication caught my attention today. The patterns of feathers are something that can perhaps be better understood by simulating their formation. The feather is born from a circular set of germ cells and it grows out of the follicle just as hairs and nails do. The colours on feathers arise from pigment and micro-structure. This 1901 publication by J. L. Bonhote "On the Evolution of Pattern in Feathers" examines the change in feather pattern from the bold streaks on a young sparrowhawk to the bars found in adults.

Pattern variations in the feathers of a sparrowhawk

Bonhote goes on to speculate on what patterns are more primitive and what are more derived. He expresses surprise at how such a regular pattern appears on the bird with bits of the pattern being present on separate feathers. 

More complex patterns with colours

It is quite surprising that not much work has actually gone into this in the years since. A 2004 study examines the developmental biology of feather follicles and briefly mentions colour patterns and the signalling that might be involved. I have always thought that a good approach to study them would be to build a simulation. Perhaps a Java applet that allows different types of signals and their diffusion in different ways along the ring of cells. Parameters like direction and rate of movement or diffusion should be controllable. A little animation (Note: Animated PNG that may or may not work on your browser) is given below to give the idea for a high-school programming project.

A rough indication for a feather simulation applet. Here two signals diffuse inwars to create a U pattern on a feather.

It would be great if an applet that has different kinds of diffusion patterns along the germ cells in the feather follicle could simulate the whole gamut of patterns one sees in nature and perhaps find some that are as yet unknown.

Further reading

• Yu et al. (2004) The developmental biology of feather follicles. Int. J. Dev. Biol. 48: 181-191.
• Shell patterns