I would prob'ly stay away from the walnut family, too... Walnut, butternut, etc. They produce a chemical (juglone) that inhibits the growth of other plants. I have no idea if it does anything to birds, but I wouldn't take the chance.
And, speaking of maple buds in the spring, I found out last spring that basswood leaves are edible when they are newly flushed, and still small and tender. They taste a bit lemony.