Naming the world’s fastest bird isn’t as easy as it seems. It’s not as simple as merely measuring the speeds at which the various types of birds fly. There are other factors involved, such as how long the bird could maintain the speed, as well as the particular species of the bird itself.
Falco peregrinus, the Peregrine Falcon, is usually considered, not just as the fastest bird in the world, but also as the fastest among all the animals on Earth. The Peregrine exhibits this speed with its hunting dive, wherein in first soars to a high altitude before it steeply dives at a rate of more than 200 miles per hour (320 kilometers per hour), then hits its prey with one wing so that it does not harm itself upon impact. A research conducted on the physics of an ideal falcon’s flight yielded that the Peregrine’s theoretical speed limit when flying at low altitudes is 250 mph (400 km/h), while its speed limit at high altitudes is 390 mph (625 km/h).
However, the Peregrine Falcon’s position as the world’s fastest bird is actually in dispute. It has been argued that the Peregrine only achieves such great speed when it is performing its hunting dive, but otherwise, it is not so exceptionally fast in level, sustained flight. By this standard, it has been proposed that the fastest bird in the world would have to be Hirundapus caudacutus, the Spine-tailed Swift. Also known as the Needle-tailed Swift or the White-throated Needletail, it is capable of flying at speeds of up to 105 mph (170 km/h).
Of course, not all birds are capable of flight. And if we are to determine which member of the bird family is indeed the fastest, perhaps we should put their landlocked relatives into consideration as well. As far as flightless birds go, Struthio camelus, the Ostrich, is recognized as the largest living bird species and is often noted for its running speed. An Ostrich is capable of running at a rate of 45 mph (72.4 km/h), considered as the top land speed rate of any species of bird.
The swiftness of the Ostrich is attributed to its large, strong legs and the unique characteristics of its feet. Whereas most birds usually have four toes on each foot, the Ostrich has only two, which apparently contributes greatly to its running ability. In addition, the nail of the bigger inner-toe resembles a hoof, while the outer-toe does not have a tail. So while it’s a toss-up between the Peregrine Falcon and the Spine-tailed Swift for the title of fastest bird in the air, no one has yet caught up with the Ostrich as the fastest bird on land.