If you can push the boat out in regards to budget I would look at the Nikon D200 and the Nikon 18-200 DX VR lens.
The D200 produces excellent quality images and also has the advantage of some weather sealing to help with the conditions you say you'll be facing... the 18-200 DX VR lens has probably all the range you'd need so no lens changing, and is one of (if not) the sharpest in it's class so you've got great image quality there too, it also has the advantage of having VR (Vibration Reduction) which is very helpful when hand holding at the longer end of the zoom or in lower light conditions.
A great combo, if you can stretch to it.
Oh, and welcome to Pixalo!
