What is the average weight in kilograms of the heaviest flying bird?

The average weight of the heaviest flying bird, which is generally recognized as the Wandering Albatross, is typically around 18 kilograms. This bird is known for its impressive wingspan and ability to glide long distances over the ocean. The weight of 18 kilograms is representative of the average range for adult Wandering Albatrosses, making it a reliable figure in ornithological studies.

Other options, while they could reference other large birds, do not accurately depict the average weight of the heaviest flying bird. For instance, while a weight of 15 kilograms might relate to some large but not heaviest species, and the weights of 20 kilograms or 25 kilograms are higher than the established average for the Wandering Albatross, leading them to be less accurate in this context. Thus, 18 kilograms stands out as the correct answer given the current knowledge of avian weights.