At some of these locations a good DSLR, with a telephoto lens having a focal length of 200mm will suffice, as you can get fairly close to the animals, but generally you'll need a 300mm lens or longer, and 400mm or longer could be a real help.
I found that even in the Galapagos Islands, off the coast of Ecuador, which Charles Darwin's book, “Origin of Species,” made famous, where many of the birds and other wildlife have a small “circle of fear,” you often need a lens with a 400mm focal length.
The “Circle of Fear” is the distance from an animal, inside of which, the animal has discomfort or distress from the photographer's or observer's presence, which may cause the animal to flee.
In other locations, such as an African safari, or a hike in Denali, a super-telephoto focal length of 500mm or more is virtually a “must.”