How did a frog get in the birdhouse????

Well Toony...that is THE question. We have so many frogs in our back yard and lots of tree frogs...but this guy did not look like your usual tree frog. The funny thing was that a few weeks later (he lived there for quite a while); he showed up in another one of our birdhouses! He was very odd and I loved him for that. Since then we have had one other little frog in that same bird house. Hmmmmmm...maybe these frogs really do have wings and I can't see them because all I can see is their slimy little heads. HA!