Catherine - You have a GREAT bird habitat there! Seriously, it looks like a great place to sit and do some bird watching. I like places like that in my garden that are partially hidden (like a Secret Garden). You've also got a LOT of terrific bird loving plants there too. Perfect!
From Wikipedia:
http://en.wikipedia.org/wiki/J...
"Toxicity:
The roots, nut husks, and leaves secrete a substance into the soil called juglone that is a respiratory inhibitor to some plants. A number of other plants including apples, tomatoes, and white birch are poisoned by juglone, and should not be planted in proximity to a black walnut. Horses are susceptible to laminitis from exposure to black walnut wood in bedding."
