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A number of animals have evolved aerial locomotion, either by powered flight or by gliding. Flying and gliding animals have evolved separately many times, without any single ancestor. Flight has evolved at least four times, in the insects, pterosaurs, birds, and bats. Gliding has evolved on many more occasions. Usually the development is to aid canopy animals in getting from tree to tree, although there are other possibilities. Gliding, in particular, has evolved among rainforest animals, especially in the rainforests of Asia (most especially Borneo) where the trees are tall and quite widely spaced.

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Types of aerial locomotion

  • Falling: Decreasing altitude under the force of gravity, using no adaptions to increase drag or provide lift.

  • Parachuting: Defined as falling at greater than 45 degrees from the horizontal with adaptations to increase drag forces. In very small animals they may be carried up by the wind.

  • Gliding: Defined as falling at less than 45 degrees from the horizontal. Lift caused by some kind of aerofoil mechanism, allowing slowly falling directed horizontal movement. Streamlined to decrease drag forces to aid aerofoil. Often some manuverability in air. Gliding animals have a lower aspect ratio (wing length/wing breadth) than flyers.

  • Flying: Flapping of wings to produce thrust. May ascend without the aid of the wind, as opposed to gliders and parachuters.

  • Soaring: Appears similar to gliding but is actually very different, requiring specific physiological and morphological adaptations. The animal keeps aloft on rising warm air (thermals) without flapping its wings. Only large animals can be efficient soarers.

The forms of aerial locomotion are not mutually exclusive and indeed many animals will employ two or more of the methods.

Two other common forms of aerial locomotion for humans are not employed in the rest of the animal kingdom: heli-propulsion and the balloon.

Ecology of aerial locomotion

Although only four groups of animal have evolved flight, all three extant groups are very successful, suggesting that flight is a very successful strategy once evolved. Bats, after rodents, have the most species of any mammalian order, about 20% of all mammalian species. Birds have the most species of any class of terrestrial vertebrates. Finally insects have more species than all other animal groups combined.

Flying animals may have evolved from gliding animals. However gliding is not necessarily just an evolutionary route to flying and has some advantages of its own. Gliding is a very energy efficient way of travelling from tree to tree. An argument made is that many gliding animals eat low energy foods such as leaves and are restricted to gliding because of this, whereas flying animals eat more high energy foods such as fruits, nectar, and insects. In contrast to flight, gliding has evolved independently many times (more than a dozen times among extant vertebrates), however these groups have not radiated nearly as much as have groups of flying animals.

One point of interest is the distribution of gliding animals. Many gliding animals are found in Southeast Asia, some in Africa, and there are no gliding vertebrates in South America. However, many more animals in South America have prehensile tails than in Africa and Southeast Asia. It has been argued that gliding animals dominate in Southeast Asia as the forests are less dense than in South America. In dense forest there is not room to glide, but a prehensile tail is very useful for moving from tree to tree. Also South American rainforests tend to have more lianas as there are less large animals to eat them compared to Africa and Asia, these lianas would aid climbers but obstruct gliders. Curiously Australia contains many mammals with prehensile tails and also many mammals which can glide, in fact all Australian mammalian gliders have tails that are prehensile to an extent.

Only a few animals are known to have specialised in soaring, the larger of the extinct pterosaurs, and some large birds. Powered flight is very energetically expensive for large animals, but for soaring their size is an advantage as it allows them a low wing loading, that is a large wing areas relative to their weight, which maximizes lift. Soaring is very energetically efficient.

Biomechanics of aerial locomotion

The forms of aerial locomotion for which the biomechanics are most studied are bird flight and insect flight. The UCMP exhibit on vertebrate flight contains a broad introduction to the biomechanics of flying and gliding vertebrates . .

Limits and extremes

Flying/soaring

  • Largest. The largest known flying animal ever used to be thought to be the pteranodon with a wingspan of up to 7.5 m. However the recently discoverd Quetzalcoatlus is much larger, with estimates of the wingspan ranging from 9 m to 18 m. The Quetzalcoatlus is considered to be at the biophysical limit of size of a flying animal, however it should be noted that the same was once said for pteranodon. The heaviest living flying amimal is the great bustard at 21 kg. The wandering albatross has the greatest wingspan of any living flying animal at 3.63 m. Among living animals which fly over land the Andean condor and the marabou stork have the largest wingspan at 3.2 m.

  • Smallest. There is no real minimum size for getting airborne. Indeed there are many bacteria floating in the atmnosphere that constitute part of the aeroplankton. However to move about under one's own power and not be overly affected by the wind requires some size.

  • Slowest. Most flying animals need to travel forward at a minimum speed to stay aloft. However some creatures can stay in the same spot, known as hovering, either by rapidly flapping the wings, as in hummingbirds, hoverflies, dragonflies, and some others, or carefully using thermals as in some birds of prey. The slowest flying non-hovering bird recorded is the American woodcock at 8 km/h, however many insects probably fly much slower than this.

  • Most maneuverable. A number of flying animals are known for their maneurability. Many animals that can hover are often very maneuverable, being able to move in any direction as well as stay still. Other flying animals known for their aerial acrobatics are bats and crows.

Gliding/Parachuting

  • Most efficient glider. This can be taken as the animal that moves most horizontal distance per metre fallen. Possible candidates are the flying squirrels which are known to glide up to 200 m and flying fish has been observed to glide for hundreds of meters on the drafts on the edge of waves with only their initial leap from the water to provide height.

  • Most maneuverable glider. Paradise tree snakes, Chinese gliding frogs, and gliding ants have all been observed as having considerable capacity to turn in the air. Many other gliding animals may also be able to turn, but which is the most maneuverable is difficult to assess.

  • Most efficient parachuter. This could be the animal that is the slowest falling, or the animal that is slowest falling given its weight.

Animals which parachute, glide, or fly (living)

Invertebrates

Arthropods
  • Insects (flight). The first of all animals to evolve flight, insects are also the only invertebrates that have evolved flight. The species are too numerous to list here. Insect flight has been studied in some detail, but less than bird flight.

  • Gliding ants (gliding). These flightless insects have secondarily gained some capacity to move through the air. Gliding has evolved independently in a number of arboreal ant species from the groups Cephalotini, Pseudomyrmecinae, and Formicinae (mostly Camponotus). All arboreal dolichoderines and non-cephalotine myrmicines except Daceton armigerum do not glide. Living in the rainforest canopy like many other gliders, gliding ants use their gliding to return to the trunk of the tree they live on should they fall or be knocked off a branch. Gliding was first discovered for Cephalotes atreus in the Peruvian rainforest. Cephalotes atreus can make 180 degree turns, and locate the trunk using visual cues, succeeding in landing 80% of the time. See Yanoviak et al 2005. Unique among gliding animals, Cephalotini and Pseudomyrmecinae ants glide abdomen first, the Forminicae however glide in the more conventional head first manner. The following page has some good videos of gliding ants. *

  • Spiders (parachuting). The young of some species of spiders travel through the air by using silk draglines to catch the wind, as may some smaller species of adult spider, such the money spider family. This behavior is commonly known as "ballooning". Ballooning spiders make up part of the aeroplankton.

Molluscs
  • Flying squid (gliding) Several oceanic squids, such as the pacific flying squid, will leap out of the water to escape predators, an adaptation similar to that of flying fish. Smaller squids will fly in shoals, and have been observed to cover distances as long as 50 meters. Small fins towards the back of the mantle do not produce much lift, but do help stabilize the motion of flight. They exit the water by expelling water out of their funnel, making the flying squid the only animal with, at a push, jet-propelled aerial locomotion .

Vertebrates

Fish
  • Flying fish (gliding). There are over 50 species of flying fish belonging to the family Exocoetidae. They are mostly marine fishes of small to medium size. The largest flying fish can reach lengths of 45 cms, but most species measure less than 30 cms in length. They can be divided into two-winged varieties and four-winged varieties. The glides are usually up to 30-50 meters in length, but some have been observed soaring for hundreds of metres using the updraft on the leading edges of waves. The fish can also make a series of glides, each time dipping the tail into the water to produce forward thrust. It has been suggested that the species Exocoetus is on an evolutionary borderline between flight and gliding. It flaps its enlarged pectoral fins when airborne, but still seems only to glide, as there is no hint of a power stroke.

Amphibians
  • Rhacophoridae flying frogs (gliding). Gliding has evolved independently in two families of tree frogs, the Old World Rhacophoridae and the New World Hylidae. Within each lineage there are a range of gliding abilities from non-gliding, to parachuting, to full gliding. A number of the Rhacophoridae have adaptation for gliding, the main feature being enlarged toe membranes. For example, the Malayan flying frog glides using the membranes between the toes of its limbs, and small membranes located at the heel, the base of the leg, and the forearm. Some of the frogs are quite accomplished gliders, for example, the Chinese gliding frog Polypedates dennysi can maneuver in the air, making two kinds of turn, either rolling into the turn (a banked turn) or yawing into the turn (a crabbed turn).
  • Hylidae flying frogs (gliding). The other frog family that contains gliders.

    Reptiles
    • Draco lizards (gliding). There are 28 species of lizard of the genus Draco, found in Sri Lanka, India, and Southeast Asia. They live in trees, feeding on tree ants, but nest on the forest floor. They can glide for up to 100 m, but usually only glide up to 20-30 m between trees as forest trees are often not so widely spaced. Unusually, their patagium (gliding membrane) is supported on elongated ribs rather than the more common situation among gliding vertebrates of having the patagium attached to the limbs. When extended, the ribs form a semi-circle on either side the lizards body and can be folded to the body like a folding fan.

    • Gliding Lacertids (gliding). There are two species of gliding lacertid, of the genus Holaspis. Found in Africa. They have fringed toes and tail sides and can flatten their bodies for gliding.

    • Ptychozoon flying geckos (gliding). There are six species of gliding gecko, of the genus Ptychozoon, from Southeast Asia. These lizards have small flaps of skin along their limbs, torso, tail, and head that catch the air and enable them to glide.

    Birds
    • Birds (flying) Again the species are too numerous to nominate. Bird flight is probably the most studied form of aerial locomotion in animals.

    Mammals

    • Feather-tailed possums (family Acrobatidae) (gliding). This family of Marsupials contains two genera, each with one species. The Feathertail Glider (Acrobates pygmaeus), found in Australia is the size of a very small mouse and is the smallest mammalian glider. The Feather-tail Possum (Distoechurus pennatus) is found in New Guinea. Both species have a stiff-haired feather-like tail that helps it steer in the air.

      • Flying squirrels (subfamily Petauristinae) (gliding). There are 43 species divided between 14 genera of flying squirrel. Flying squirrels are found almost worldwide in tropical (Southeast Asia, India, and Sri Lanka), temperate, and even Arctic environments. They tend to be nocturnal. When a flying squirrel wishes to cross to a tree that is further away than the distance possible by jumping, it extends the cartilage spur on its elbow or wrist. This opens out the flap of furry skin (the patagium) that stretches from its wrist to its ankle. It glides spread-eagle and with its tail fluffed out like a parachute, and grips the tree with its claws when it lands. Flying squirrels have been reported to glide over 200 m.

      • Anomalure or scaly-tailed flying squirrels (Anomaluridae family) (gliding). These brightly coloured African rodents are not squirrels but have evolved to a resemble flying squirrels by convergent evolution. There are seven species, divided in three genera. All but one species has gliding membranes between their front and hind legs. One genus is particularly small and is known as flying mice, but similarly they are not mice.

      • Colugos or Flying lemurs (order Dermoptera) (gliding). There are two species of flying lemur. This is not a lemur, which is a primate, but molecular evidence suggests that colugos are a sister group to primates, however some mammologists suggest they are a sister group to bats. Found in Southeast Asia, the colugo is probably the mammal most adapted for gliding, with a patagium that is as large as geometrially possible. They can glide as far a 70 m with minimal loss of height.

      • Bats (flying). There are many species of bat, again too numerous to nominate. This group may be polyphylous.

      • Cats and maybe others. (very limited parachuting). If they fall cats spread their bodies to maximise drag, a very limited form of parachuting. Cats have an innate 'righting reflex' that allows them to rotate their bodies so they fall feet first. Some other animals may show similar very limited parachuting.

      Animals which parachute, glide, or fly (extinct)

      Reptiles

      • Sharovipteryx (gliding). This strange lizard, sometimes proposed as a pterosaur ancestor, from the Upper Triassic of Kirghiia unusually had a membrane on its elongated hind limbs, whereas most flyers or gliders tend to have elongated fore limbs if their limbs are elongated. In some reconstructions they had webbing on the forelimbs and neck as well.

      • Longisquama insignis (possibly gliding/parachuting). This small reptile may have had long paired feather-like scales on its back. They may have been used for parachuting and/or display.

      • Scleromochlus (gliding). An ancient gliding reptile, like sharovipteryx suspected to be an ancestor of pterosaurs.

      • Pterosaurs (flying). There were many species of this winged reptile.

      Birds

      • Theropods (gliding/flying). The theropods were dinosaurs, many of them were feathered, and they are suspected to be ancestors and sister species to birds. Some species (Microraptor gui, Microraptor zhaoianus, and Cryptovolans pauli) have been found that were fully feathered on all four limbs, giving them four 'wings' that they are believed to have used for gliding or flying.

      References

      • Yanoviak, S. P., R. Dudley and M. Kaspari. 2005. Directed aerial descent in canopy ants. Nature 433: 624-626.
      • Packard, A. 1972. Cephalopods and fish: the limits of convergence. Biol. Rev. 47: 241-307.
      • Xing Xu, Zhonghe Zhou, Xiaolin Wang, Xuewen Kuang, Fucheng Zhang and Xiangke Du. 2003. Four-winged dinosaurs from China. Nature 421: 335-340
      • Schiøtz, A. & H. Vosloe. 1959. The gliding flight of Holaspis guentheri Gray, a west-African lacertid. Copeia, 1959: 259-260.
      • Arnold, E. N. 2002. Holaspis, a lizard that glided by accident: mosaics of cooption and adaptation in a tropical forest lacertid (Reptilia, Lacertidae. ). Bulletin of The Natural History Museum. Zoology Series 68: 155-163
      • McGuire, J. A. 2003. Allometric Prediction of Locomotor Performance: An Example from Southeast Asian Flying Lizards. The American naturalist 161: 337–349.
      • McKay, M. G. 2001. Aerodynamic stability and maneuverability of the gliding frog Polypedates dennysi. The Journal of Experimental Biology 204: 2817-2826. html

      External links

      Animals | Natural history | Locomotion

 

This article is licensed under the GNU Free Documentation License. It uses material from the "Flying and gliding animals".

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