Marc

Good question - quick answer is to take both. Estes is a contributor to NAS - NAS has color plates and goes beyond mammals to reptiles, birds, insects etc. The value of Estes is the depth of observable behavior of animals you will be seeing. In terms of weight/value and balanced with a practical consideration of time available for reading on safari (napping will be a powerful attraction for inter-game drive breaks!)I would opt for Estes as a single source. But, again, I am not a compulsive birder - if you are, go with NAS.

Ted