Why is the ostrich noted in terms of its physical abilities?

The ostrich is primarily noted for its impressive running abilities, making it the fastest running bird on foot. Capable of reaching speeds up to 45 miles per hour, the ostrich's long legs and unique body structure are specially adapted for swift, powerful movements. Its running speed is a significant attribute that allows it to escape predators in its natural habitat, solidifying its reputation as a fast, terrestrial bird.

The other options do not accurately represent the ostrich's capabilities. For example, while many birds are capable of flight, the ostrich is flightless, which eliminates the notion of it flying the highest; it is also not the heaviest flying bird since it does not fly at all. Additionally, while ostriches do build nests, they are not notably the largest among birds when considering overall size in relation to nesting. Thus, the correct focus remains on the ostrich's exceptional speed and adaptation for running.