I am a totqal rookie at wildlife myself. My limited experience is landscapes and macros going over.
The most challenging shots are the "into the sunset" shots. This is especially true when subjects like elephants are below the horizon. If you just point and shoot you may get good sky colors, but below the horizon will just be dark. For both of the shots you refer, they were shot from a pontoon boat and silhoutte was ok.
My South African travel friends advised:
1) look at the histogram often! In particular, make sure you are not too heavy on that left edge. Their is more data on center to right, so what appears "blown" can be recovered their, but dark shots will only give you a lot of noise if you try to push these in photoshop.
2) My camera let me bias 2 f-stops and I usually did while shooting into sunset. I think the MkII and MkIII will give you 3 full stops.
3) You can shoot a lot more than you think after the sun has set, so keep shooting for a while, but keep the shutter speed up.
4) Use a beanbag on EVERY shot to stabalize. I only used my monopod on a very few night light shots of baobobs, etc.
5) as noted before, most were shot at ISO 400 on my 30D, but if I had a MkIII or a 40D, I probably would have shot more at ISO 640 to get more light and shutter speed.
6) anticipate where moving/grazing animals will be and position ahead. You may think you are wasting 15 minutes, but the patience allows you to see more and be prepared.
7) spot meter at sunset if animals are below horizon.
8 ) bracket the shot. I tried to keep f-stop above f8 so I had some dof with my tele, but that really cost me shutter speed. I bracketed anyway.
9) final learning: Wildlife is really great, but don't forget to shoot the people. Road scenes, kids, soccer games, etc.
Since I was shooting mostly with telephoto, I never tried graduated ND filters on the trip, but once I started editing the shots, I wish I had done this a little to allow better metering of foreground without over exposure.
Also, one last debate point. Since the exposure levels are soooooo broad, HDR of single frames has worked very well for me on images I have printed large. A few of those are on the link I provided such at this one: http://www.flickr.com …in/set-72157604081437686/
Good luck on the trip.