Request #141

I have been searching for this book off and in for a few years now but I cannot find d it anywhere. I remember it being about a boy protagonist, most likely a teenager who goes to live with a family that seems completely perfect and happy. They have a daughter about the boys age and they go birdwatching together and are on the hunt for a specific bird. The boy realizes that the family is really strict and kind of controlling, and the daughter reveals that all the classic novels she reads are actually just magazines inserted into the bindings. The parents accuse the boy of being a bad influence on the girl but I don’t remember how it ends.