What camera should I purchase?

I'm traveling to India next month and I'm looking for a camera to take great pictures with. I should mention I'm a beginner and am on a budget. Since everything we will be doing involves biological work, I want to capture wildlife and other things outdoors. I do however want the camera for personal use as well when I get home. So far I have been looking at the Canon Rebel T3 and Nikon D3100.Im leaning towards the Nikon right now. Is there any other cameras I should be looking at? And if not, which one would you recommend? Also what is the thought on used cameras?

Either of those will suit you fine and set you up for life inside of a good system of lenses and accessories. The lens you choose to put on it is the more critical issue. Work out what the majority of your shots will be and if real macro will be important. Otherwise just ensure that you can shoot good enough close-ups from the long end of the focal range so that the confusing background blurs out.

For example I have an 18-135 on my Sony A57 (walk around test shots in the gallery below)
but I still need to keep my Tamron f2.8 macro lens as well.

http://www.pbase.com/johnfr/sony_18135

and a couple of Tamron macro shots:
http://www.pbase.com/johnfr/image/147186254
http://www.pbase.com/johnfr/image/77285036