Songbird Essentials Eco Friendly Recycled Plastic Window Mounted Nest View Birdhouse Nesting Box Durable, weather resistant recycled plastic nest box attaches to a window or smooth surface using strong suction cups Clear back panel allows you to see the birds building their nest and raising their young Entrance hole measures 1 1/2 inch and box measures 8" x 6.5" x 5.5" Great way to introduce children or grandchildren to birds, but also a treat to watch birds use this nesting box no matter your age Makes a great gift