I have a magazine at home that has a project to use a Pi2b computer with a camera for input. The board costs less that $100, and the camera (if with IR as well) about $35. I don't recall it needing an Arduino board, just the Pi and the camera, and of course, some work. I will try to recall getting the name of the correct magazine and issue.
Also,
http://www.raspberry-pi-geek.com/Archive/2015/10/Building-a-video-enabled-nest-box shows you a simple bird house to make.
I have thought from time to time that I would like to do some bird photography. But as interesting as the Pi project looks, especially with IR, I would be more interested in using film cameras. Tripods, small tents as blinds, and long lenses, all would work well. I also once saw a birdhouse without a back that was butted up against a window. I think it had some kind of blind at the back, either opaque or providing less light than from outside, so birds couldn't see in the house and get spooked. That would surely provide a chance to watch, but photography might be a little more difficult without IR film. Or, carefully prefocused and not too often used electronic flash might be OK; the birds might think of it like lightening.
Good luck. Sounds like you and your wife are going to have a lot of fun together time with bird watching.
