Fastest animals
The fastest land animal is the cheetah, which has a recorded speed of . The peregrine falcon is the fastest bird and the fastest member of the animal kingdom with a diving speed of . The fastest animal in the sea is the black marlin, which has a recorded speed of .
Cetacean surfacing behaviour
"Porpoising", also known as running, is a high speed surface behaviour of small cetaceans where long jumps are alternated with swimming close to the surface. Despite the name, porpoising behaviour is seen in dolphins and porpoises, as well as other marine species such as penguins and pinnipeds. When marine mammals are travelling at speed they are forced to stay close to the surface in order to maintain respiration for the energetic exercise. At leisurely cruising speeds below 4.6 m/s, dolphins swim below the water's surface and only briefly expose their blowholes along with up to one third of their body at any one time. This results in little splashing as they have a very streamlined shape. Porpoising occurs mainly when dolphins and porpoises are swimming at speeds greater than 4.6 m/s. Here, jump length is roughly equal to distance traveled when the cetaceans are submerged. This exposes the blowhole for longer which is needed to get enough oxygen to maintain metabolism and therefore high speeds over long periods of time. Studies have also shown that leaping is more energetically efficient than swimming above a certain threshold speed. This is due to the reduction in friction when travelling in air compared to water which saves more energy than is needed to produce the leap. These benefits also outweigh the energy wasted due to the large amount of splashing often seen when groups are porpoising. Porpoising is therefore a result of high speed swimming which cetaceans use for important pursuit and escape activities. For example, dolphins may be seen porpoising away from their main predator, sharks or the direction of incoming boats to avoid collision.