Depending on your shooting style and the type of photography you want to take. For bald eagles in Alaska, a 300mm will still be short using a DX camera. General walk-around will be the 18-105mm VR, 18-200mm, and 16-85mm if you want to stick with Nikon. Something a little more versatile but on the heavy side is the Nikon 28-300mm. My favorite walk-around lens on FX is the 24-120mm f4 which has an equivalent field of view of the 16-85mm DX lens.