Virginia Lee at The Rogers' Family Blog has a wonderful bird unit that has been helpful to me in creating our own bird unit. We recently did her bird beaks experiment, which I tweaked a bit.
Here are our supplies: scissors, spoon, clothespin, and tweezers to represent different types of bird beaks and peants in the shell, a meaty bone, sardines in a bowl of water, and little noodles (worms.) And this bird beak printout.
We are doing a longer term experiment to see which birds prefer black oil sunflower seeds and which prefer safflower seeds. We just nailed a couple yogurt lids to the deck rail for simple feeders.
We've also been reading The Thornton Burgess Bird Book for Children.
And I made a bird bingo game with pictures of common birds to help the kids learn their names.