One more usage for CD boxes! A Great Kiskadee made its nest on the window of an external room of our house.
My son is a Biologist and Nature Photo enthusiast and decided to follow the growth of the lil' bird in the nest and we decided to gain access to the nest without being a hassle for the birds, well, almost...

Step 1: The Making Of

We chose to fit a hardboard piece between the two window panes just to be quick and easy.
After measuring the available space we've cut the board to size and opened the window cutout, about a half an inch less than the CD case size. Then we glued the CD case with hot melt glue. Be sure to round the tips of the case hinges in order to let it move without going further than the case thickness. We used a piece of sanding paper. Next place any kind of opening helper, such like this wood dowel.

Step 2: And Voila!

Cut out, using a pair of scissors, a back door in the nest taking care to not put your hands inside as it would make the Kickadee to abandon the nest and, most important, avoid decapitating the birds inside. Insert the board between the window panes, and be happy!