Last year we had a problem in that one of the tits started roosting in the area at the top of the box next to the camera. We presume she found it warm and cosy up there. A short while later she found the cables leading to the camera and started pecking at them. Fearing that they would get damaged, I inserted a small sheet of glass, preventing the bird's access to the top. The picture alongside shows the relevant parts of the tit box. The bird was getting up through the round hole in the plywood panel at the top of the box where the gap between the panel and the camera support with the box closed is about an inch.
This solution was initially quite satisfactory. However, as time passed, the glass plate became dusty and the quality of the pictures suffered. This was particularly true near the end of their stay as the young chicks frequently exercised their wings by flapping furiously inside the box and this stirred up even more dust and dirt.
This year I have made an open ended cardboard cylinder that fits exactly into the circular hole. Its bottom end is glued to the bit of plywood with the hole. Its top end rests against the piece of wood that you can see in the picture that is supporting the camera. The bird therefore cannot get up to the attic, but the camera's view of the nest is not affected. We hope that this will solve the problem.