Hi again and thank you all for your suggestions! I have seen Phillip Torrone's description of a hacked digital camera and I think it seems promising. However, the timer he uses (555) seems a bit inaccurate for my long exposure intervals, and if you want the shots to be taken at noon each day you also have to start up the camera at that time. I was hoping to combine a digital camera with a small digital travel alarm clock. This way I could easily program the daily exposure time and start up the system at any time of the day. I don't know how difficult this would be since I am not very familiar with electronics, but that's where guys like you come in! Is this a way forward or not?
To keep the costs down I would probably, like Phillip Torrone, use an old second-hand digital camera. The $600 videocam solution is way over my budget and nothing I would like to leave in the forest unattended for weeks.
Keep up the good work!