well, do you happen to have any sort of video capture device on your computer? a video card with a video input perhaps?
since you desire greater than 30 minutes of filming outside, i would say your best bet would be a normal HI-8 or Mini DV (digital) video camera.
Basically, the type anyone uses to film things. (family outings, vacations, etc).
Then, when you want a webcam, you can get different types of software that will allow you to capture still images from your camera when it is hooked up to the video input.
There's no real "webcams" that can record for over 30 minutes w/out being attached to a computer.