What is the strongest bird ?

hmmm... maybe the Ostrich or Emu? I really don't know, but those birds are huge!

I think the strongest bird for me is an eagle. Eagles are large birds of prey which inhabit mainly the Old World, with only two species (Bald Eagle and Golden Eagle) commonly found in North America, a few in South America, the (White-bellied Sea Eagle, Wedge-tailed Eagle) in Australia and the Philippine Eagle in the Philippine Archipelago. They are members of the bird order Falconiformes (or Accipitriformes, according to alternative classification schemes), family Accipitridae and belong to several genera which are not necessarily closely related to each other. Eagles are differentiated from other broad-winged birds of prey mainly by their larger size, more powerful build, and heavier head and bill. Even the smallest eagles, like the Booted Eagle, which is comparable in size to a Common Buzzard or Red-tailed Hawk has relatively longer and more evenly broad wings, and more direct, faster flight. Most eagles are larger than any other raptors apart from the vultures. Like all birds of prey, eagles have very large powerful hooked beaks for tearing flesh from their prey, strong legs, and powerful talons. They also have extremely keen eyesight to enable them to spot potential prey from a very long distance. This keen eyesight is primarily contributed by their extremely large pupils which cause minimal diffraction (spreading) of the incoming light. http://en.wikipedia.org/wiki/Eagle