I just watched the show on building a habitat for the green heron. In the show you made a peanut feeder using yarn. I don't know what kind of yarn you used in the project and I never heard you give any cautions, so I wanted to mention that any time you use yarn it should NEVER be acrylic or nylon, etc. It should ALWAYS be a natural fiber. Natural fibers will deteriorate and fall off or are easier for the bird/animal to cut through or pull off.
The man made fibers will get wrapped around the birds legs/feet cutting off circulation eventually causing the limb to die. It must be horribly painful as well. This happened with a Zebra Finch I had. By the time I saw signs of a problem it was too late. The vet couldn't get hold of the fibers because the leg had swollen around the fibers so much. The bird died of a heart attack because of the trama.

Thanks for pointing this out!

David Mizejewski
Naturalist, National Wildlife Federation
Host, Animal Planet's Backyard Habitat