Hair of the Dog(s)

The other day I saw a Carrion Crow fly up from my neighbour's garden with something fluffy in its bill.  I could not make out what it was and it did not look like a food item.  Then yesterday my neighbour showed me a photo she had taken of a Crow sorting through a pile of dog hair she had put out for them.  She has pretty, long-haired Sheltie dogs and over the winter she saves the groomings and puts them out for the birds. The crows pick it over and fly off with beakfulls of it to line their nests.  I had never heard of people doing this before, but my wife tells me that her aunt used to do it.  She had a Collie and kept its groomings and put them out in her garden in the spring.