Our bedding supplies are accepted!
I took the photo above yesterday morning. As you can see, at least a third of the cat fur is gone! I didn't actually see any birds come by to take the fur until about an hour later. I was indoors and heard an oak titmouse singing very loudly.
I looked out the front door to see if it was anywhere near the nest supply cage. And there it was, sitting on top of the cage, pulling at a wad of fur. It was too fast for me to get a photo of it on the cage. But then the wad of fur fell in the grass and the oak titmouse decided to pick it up from there, and then flew away with its treasure.
Yes, some of the fur apparently falls out when the birds are pulling at it. I go outside now and then and stuff the fur clumps back into the cage.
Oak titmouse gathering fur
Early this evening, after 5 pm, a chestnut-back chickadee sat on top of the cage, pulling at a big clump of fur. I happened to be walking by and stood about 4 feet away from the bird as it busily pulled the clump apart into fine strands and stuffed its beak with the strands. By the time it flew away to its nest, the chickadee looked like it had a huge fluffy white beard.