02 October 2013

Air erodes feathers

Primary feathers from left and right wings, thinner on the fore-edge.
Erosion is evident on both edges.

From July on, the crows are in moult, even the ones that hatched out in the summer. The feathers that grew in beginning last July work their way out, and new feathers grow. There is a period of more than two months when crows lose their glossy black and become not just a drab brown, but because of the feathers coming out and the feathers coming in, they look like a medieval band of lepers. This is when you see bits of their insulating undercoat made up of little fluffy grey feathers.

Crow at the worst stage of moult.

Air -- and sunlight -- erodes feathers. The brilliant black that sometimes flashes blue and purple in the right angle of light is a matter of refraction, not only of melanins. During the year the structure of the feathers that refracts the gloss wears down, and at the end of summer crows show the underlying pigments. 

Not all of our crows are evenly-pigmented.  The Korax family has patches of lighter-colored feathers all year around, some of them with a light ring around the neck. They are not discriminated against by the black crows.

The fore-edges of the wings gradually deteriorate.  Brushing against the nest, or tree branches and telephone poles, or other crows, wears down feathers. If you want to see nearly perfect feathers, go to this site created by the US Fish and Wildlife Service where you can identify most of the individual feathers from 100+ species of birds. 

It is illegal to possess these feathers.  I brought them inside to scan, and then returned them to the outdoors, to the crow shrine.  We have a place on the edge of the yard where we put odd things dug up in the course of gardening -- strange-shaped rocks, enormous nails used for railroad ties, crow feathers. Passers-by sometimes take the stones, never the feathers. As far as I can tell, when the crows eat cracked corn beside the feathers, they never notice them.  

I am fascinated by the evidence of the seasons, something I take for granted with the trees, with the plants in the garden. When the chlorophyll in leaves breaks down at the end of summer, we see the underlying carotene and anthocyanin pigments. Until this year, I had never made the connection across the species between the change of leaf color, and the change of crow color, between shedding leaves, and shedding feathers.  But that analogy goes only so far.  One of the Korax family came up to the car when I drove into the driveway this afternoon, and I saw the glossy black of the new feathers, not fully grown out.

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