Tradeoffs for locomotion in air and water
Encyclopedia
Certain species of fish
and bird
s are able to locomote in both air and water, two types of fluid
media with very different properties. A fluid
is a particular phase of matter that deforms under shear stresses and includes any type of liquid
or gas
. Because fluids are easily deformable and move in response to applied forces, efficiently locomoting in a fluid media presents unique challenges. Specific morphological
characteristics are therefore required in animal species that primarily depend on fluidic locomotion. Because the properties of air and water are so different, swimming and flying have very disparate morphological requirements. As a result, despite the large diversity of animals that are capable of flight or swimming, only a limited number of these species have mastered the ability to both fly and swim. These species demonstrate distinct morphological and behavioral tradeoffs associated with transitioning from air to water and water to air.
, birds
, and bat
s are capable of true, sustained, powered flight.
For birds to achieve flight, they must first successfully overcome the downward pull of gravitational forces
by producing lift
. According to Bernoulli's Principle
, a faster moving fluid produces reduced pressure than the same fluid moving at a slower speed. Because of the inherent asymmetry between the top and bottom surfaces of avian wings, also called camber
, air flow velocity over the wing is faster than below, resulting in greater pressure application to the bottom surface. This pressure differential creates a net upward force on the wing, thus allowing the bird to lift off the ground, provided the upward force exceeds its weight.
To achieve powered, forward flight birds must counteract drag forces
that act opposite the direction of flight. Drag forces acting on a flying animal are composed of parasitic drag
on the body fuselage and induced drag
on the wings, both acting against the relative direction of flight. Adjusting the angle of attack
while wing beat frequency is held constant, birds are able to direct a component of the lift produced by their wings backwards, thus producing propulsive force known as thrust
.
. The most widely accepted theories include:
, bird anatomy
has evolved to fit a particular species' behavior and lifestyle. For example, birds that live in dense forests and require high maneuverability and precise landing capabilities tend to have wing shapes and body plans that reduce stability to allow the execution of fast turns and sudden accelerations. Seabirds, on the other hand, tend to fly for extended periods in open air because land masses are distantly separated and floating on the surface of the water can be metabolically costly due to the temperature differential between air and sea water. As a result, large sea birds rely mostly on soaring flight
because it allows these animals to achieve relatively continuous lift without the added metabolic cost of flapping their wings. Because birds fly at an angle relative to the wind during dynamic soaring
, they must be able to achieve flight speeds greater than this head wind. Consequently, birds that rely on dynamic soaring tend to have high wing loading
s and high aspect ratio
s. In other words, gliding birds have wing shapes that allow them to behave more like fixed wing aircraft and rely mostly on passive gliding. Albatross
es have the largest wingspan of any extant bird, evidence of their primary reliance on aerodynamic and slope soaring
techniques to achieve their extremely long migration patterns.
In contrast, thermal soaring birds, such as Rüppell's Vulture
s, tend to have much smaller wing loadings and aspect ratios. Because the fastest rising air occurs in the center of a thermal
, these birds optimize their flight behavior by achieving very tight turning radii
. In other words, these birds tend to have smaller wings relative to body mass, which renders them less stable in gliding but gives them much more maneuverability so that they are capable of executing very tight turns.
is swimming, achieved by exerting force on the surrounding water which, by Newton's 3rd law, results in a reactive force that propels the animal forward.
can counter the downward pull of gravity, allowing these animals to float without much effort. While there is great diversity in fish locomotion, swimming behavior can be classified into two distinct "modes" based on the body structures involved in thrust production, Median-Paired Fin (MPF) and Body-Caudal Fin (BCF). Within each of these classifications, there are a numerous specifications along a spectrum of behaviors from purely undulatory
to entirely oscillatory
based. In undulatory swimming modes thrust is produced by wave-like movements of the propulsive structure (usually a fin or the whole body). Oscillatory modes, on the other hand, are characterized by thrust production from swiveling of the propulsive structure on an attachment point without any wave-like motion.
UNDULATORY
OSCILLATORY
. This form of undulatory locomotion
is termed Body-Caudal Fin (BCF) swimming on the basis of the body structures used.
UNDULATORY
OSCILLATORY
It is important to point out that fish do not rely exclusively on one locomotor mode, but are rather lomotor "generalists," choosing among and combining behaviors from many available behavioral techniques. In fact, at slower speeds, predominantly BCF swimmers will often incorporate movement of their pectoral, anal, and dorsal fins
as an additional stabilizing mechanism at slower speeds, but hold them close to their body at high speeds to improve streamlining and reducing drag. Zebrafish have even been observed to alter their locomotor behavior in response to changing hydrodynamic influences throughout growth and maturation.
In addition to adapting locomotor behavior, controlling buoyancy effects is critical for aquatic survival since aquatic ecosystem
s vary greatly by depth. Fish generally control their depth by regulating the amount of gas in specialized organs that are much like balloons. By changing the amount of gas in these swim bladders, fish actively control their density. If they increase the amount of air in their swim bladder, their overall density will become less than the surrounding water, and increased upward buoyancy pressures will cause the fish to rise until they reach a depth at which they are again at equilibrium with the surrounding water. In this way, fish behave essentially as a hot air balloon does in air.
species utilize surface feeding or plunge diving during foraging in which gravity and/or momentum
is used to counteract buoyancy effects for a short period of time. Other species can remain submerged for longer periods of time and practice pursuit diving in which they actively produce thrust to remain submerged and chase after prey. Because birds have decoupled locomotor modules, pursuit divers can produce thrust using either their wings, feet, or some combination of the two.
is primarily adapted for efficient flight. Bird species that rely on swimming as well as flight must contend with the competing requirements of flight and swimming. Morphological characteristics that are advantageous in flight are actually detrimental to swimming performance.
Light bones:
The avian skeletal system has evolved to be extremely lightweight with hollow air spaces that are highly integrated with the respiratory system. The decreased body weight resulting from these adaptations is highly beneficial for reducing the effects of gravity, thus making lift easier to achieve. Birds that swim, however, must contend with the increased buoyancy effects of having lighter bones and a reduced body mass. Instead, diving birds increase their muscle mass, resulting in an overall increase in body mass that reduces the effects of buoyancy and makes submersion easier. This effect is predominantly seen in shallow diving birds as buoyancy effects are strongest. Higher masses in diving birds appear to be correlated with higher wing loading and consequently larger wings. Faster flying speeds also result from higher wing loading which would be potentially detrimental for small flying birds that must land precisely on small branches. Diving birds, however, do not have this constraint because open water can accommodate harder landings.
Large air spaces:
Similar to having light bones, birds also have large respiratory systems with large air spaces that reduce body weight and allow more efficient oxygen exchange required for the high metabolic demands of flight. Birds also have specialized structures called air sacs closely associated with their lungs that store air when the animal inspires, further reducing body weight and maintaining the partial pressure
of oxygen within the lungs equal to that of the surrounding environment. While highly beneficial for flight, decreasing body weight (and thus whole body density) increases buoyancy forces and makes maintaining submerged depth more difficult. Swimming birds have been observed to exhale before dives, reducing their air volume and thus their overall body density. Other studies have suggested than diving birds increase their blood oxygen stores thus simultaneously reducing the amount of oxygen they must retain in their lungs when diving and allowing them to dive for longer durations.
Plumage:
Bird plumage is intended to hold and deflect air to make lift easier to achieve in flight. Again, this adaptation is detrimental to swimming because the increased air volume increases buoyancy forces. Some diving birds have been observed to preen immediately before diving, and some researchers believe that this may expel the stored air and reduce the air volume, thus increasing over all body density, decreasing buoyancy effects and making submersion easier.
Behavior:
Cormorants have been observed to alter their swimming behavior with changes in body buoyancy. When body weight (and thus buoyancy) was artificially altered, horizontally swimming cormorants reduced the angle of body tilt when additional weight was added and increased the tilt angle when weight was removed. When enough weight was added to make the birds negatively buoyant, the birds angled their bodies upwards so that the thrust produced by paddling their hind-limbs acted to keep them from sinking. In other words, these birds can dynamically adjust the tilt of their bodies to adapt to changing buoyancies. Because air spaces are compressed with increased depth, diving birds must be capable of adapting to changing buoyancies throughout a dive. In fact, both Brünnich’s Guillemots and white-winged scoter
s have been observed to alter their stroking behavior throughout a dive as an adjustment for changing buoyancies.
s, diving petrels, and penguin
s. Thrust production in these animals is produced via lift principles, much like in aerial flight. These birds essentially "fly" beneath the surface of the water. Because they have the dual role of producing thrust in both flight and swimming, wings in these animals demonstrate a compromise between the functional demands of two different fluid media.
Because the density of water is so much higher than air, the same wing excursion in either medium will produce more thrust in water. As a result, relative wing size in swimming birds tend to be smaller than comparably sized birds that fly only. Marine birds also tend to have higher than expected body mass as a mechanism to counteract buoyancy forces when submerged. The combination of smaller wings and increased body mass produce higher wing loading in these birds, consequentially resulting in faster flying speeds. While high flying speeds can be detrimental to landing on tree perches for flying birds, there is little consequence to high impact landing in water.
Birds that rely on lift based propulsion for swimming have been observed to utilize higher wing beat frequencies when flying than when submerged and swimming. This observation follows directly from the logic that the increased density of water produces greater thrust for similar wing excursions, so for a given speed fewer wing beats are needed to create identical propulsion totals. It is also suggested that lift based swimmers have higher swim speeds and greater metabolic efficiency than drag based swimmers because they are able to displace greater water volumes (thus experiencing greater reactive thrust) with their wings than a comparable sized bird can with its feet.
s, greebe
s, loon
s, and some duck
species. Like patterns seen in fish, drag based avian swimmers are more maneuverable than their lift based counterparts. As a result, drag based swimming mechanisms are more often seen in birds that live in estuarine
environments with more environmental obstacles that must be avoided.
Some swimming birds have been observed to utilize different propulsive mechanisms in different phases of a dive. Drag based swimming is most often observed in swimming birds during the foraging (or bottom) phase of a dive because it provides greater maneuverability for pursuing prey while the more efficient lift based swimming mechanisms are used during descent. Guillemot
s were observed to use lift based swimming intermittently during the ascent phase of a dive but rely mostly on passive buoyancy forces to lift them to the surface.
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While most fish have caudal fins with evenly sized lobes (i.e. homocaudal), flying fish have an enlarged ventral
lobe (i.e. hypocaudal) which facilitates dipping only a portion of the tail back onto the water for additional thrust production and steering.
Larger mass:
Because flying fish are primarily aquatic animals, their body density must be close to that of water for buoyancy stability. This primary requirement for swimming, however, means that flying fish are heavier than other habitual fliers, resulting in higher wing loading and lift to drag ratios for flying fish compared to a comparably sized bird. Differences in wing area, wing span, wing loading, and aspect ratio have been used to classify flying fish into two distinct classifications based on these different aerodynamic designs.
or Cypselurus'
' body plan, both the pectoral and pelvic fins are enlarged to provide lift during flight. These fish also tend to have "flatter" bodies which increase the total lift producing area thus allowing them to "hang" in the air better than more streamlined shapes. As a result of this high lift production, these fish are excellent gliders and are well adapted for maximizing flight distance and duration.
Comparatively, Cypselurus
flying fish have lower wing loading and smaller aspect ratios (i.e. broader wings) than their Exocoetus monoplane counterparts, which contributes to their ability to fly for longer distances than fish with this alternative body plan. Flying fish with the biplane design take advantage of their high lift production abilities when launching from the water by utilizing a "taxiing glide"
in which the hypocaudal lobe remains in the water to generate thrust even after the trunk clears the water's surface and the wings are opened with a small angle of attack for lift generation.
body plan, only the pectoral fins are enlarged to provide lift. Fish with this body plan tend to have a more streamlined body, higher aspect ratio
s (long, narrow wings), and higher wing loading than fish with the biplane body plan, making these fish well adapted for higher flying speeds. Flying fish with a monoplane body plan demonstrate different launching behaviors from their biplane counterparts. Instead of extending their duration of trust production, monoplane fish launch from the water at high speeds at a large angle of attack (sometimes up to 45 degrees). In this way, monoplane fish are taking advantage of their adaptation for high flight speed, while fish with biplane designs exploit their lift production abilities during takeoff.
Vogel, Steven (1994) "Life in Moving Fluid: The Physical Biology of Flow." Princeton University Press, Princeton, N.J. ISBN 0-691-02616-5 (SEE particularly pp115–117 and pp207–216 for specific biological examples swimming and flying respectively)
Wu, Theodore, Y.-T., Brokaw, Charles J., Brennen, Christopher, Eds. (1975) "Swimming and Flying in Nature: Volume 2.: Plenum Press, New York, N.Y. ISBN 0-306-37089-1 (SEE particularly pp615–652 for an in depth look at fish swimming and pp845–867 for a detailed analysis of vertebrate flight)
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
and bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s are able to locomote in both air and water, two types of fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
media with very different properties. A fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
is a particular phase of matter that deforms under shear stresses and includes any type of liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
or gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
. Because fluids are easily deformable and move in response to applied forces, efficiently locomoting in a fluid media presents unique challenges. Specific morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
characteristics are therefore required in animal species that primarily depend on fluidic locomotion. Because the properties of air and water are so different, swimming and flying have very disparate morphological requirements. As a result, despite the large diversity of animals that are capable of flight or swimming, only a limited number of these species have mastered the ability to both fly and swim. These species demonstrate distinct morphological and behavioral tradeoffs associated with transitioning from air to water and water to air.
Flying birds
Of extant species, only insectsInsect flight
Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how...
, birds
Bird flight
Flight is the main mode of locomotion used by most of the world's bird species. Flight assists birds while feeding, breeding and avoiding predators....
, and bat
Bat
Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, glide rather than fly,...
s are capable of true, sustained, powered flight.
Aerodynamic principles
Gravitation
Gravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force proportional to their mass. Gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped...
by producing lift
Lift (force)
A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...
. According to Bernoulli's Principle
Bernoulli's principle
In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy...
, a faster moving fluid produces reduced pressure than the same fluid moving at a slower speed. Because of the inherent asymmetry between the top and bottom surfaces of avian wings, also called camber
Camber (aerodynamics)
Camber, in aeronautics and aeronautical engineering, is the asymmetry between the top and the bottom surfaces of an aerofoil. An aerofoil that is not cambered is called a symmetric aerofoil...
, air flow velocity over the wing is faster than below, resulting in greater pressure application to the bottom surface. This pressure differential creates a net upward force on the wing, thus allowing the bird to lift off the ground, provided the upward force exceeds its weight.
To achieve powered, forward flight birds must counteract drag forces
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
that act opposite the direction of flight. Drag forces acting on a flying animal are composed of parasitic drag
Parasitic drag
Parasitic drag is drag caused by moving a solid object through a fluid medium . Parasitic drag is made up of many components, the most prominent being form drag...
on the body fuselage and induced drag
Lift-induced drag
In aerodynamics, lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, is a drag force that occurs whenever a moving object redirects the airflow coming at it. This drag force occurs in airplanes due to wings or a lifting body redirecting air to cause lift and also in cars...
on the wings, both acting against the relative direction of flight. Adjusting the angle of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
while wing beat frequency is held constant, birds are able to direct a component of the lift produced by their wings backwards, thus producing propulsive force known as thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
.
Evolution of flight
There are many competing theories explaining the evolution of avian flightOrigin of avian flight
Around 350 BCE, Aristotle and other philosophers of the time were attempting to explain the aerodynamics of avian flight. Even after the discovery of the ancestral bird Archaeopteryx, over 150 years ago, debates still persist regarding the evolution of flight...
. The most widely accepted theories include:
- Cursorial modelOrigin of avian flightAround 350 BCE, Aristotle and other philosophers of the time were attempting to explain the aerodynamics of avian flight. Even after the discovery of the ancestral bird Archaeopteryx, over 150 years ago, debates still persist regarding the evolution of flight...
: wings evolved as a stabilization mechanism for progressively longer jumps in running bipeds. - Arboreal modelBird flightFlight is the main mode of locomotion used by most of the world's bird species. Flight assists birds while feeding, breeding and avoiding predators....
: the earliest ancestors of birds were gliders rather than true fliers. Much like modern day flying squirrels, early avian ancestors were thought to climb up trees and then glide down from the tree tops. - Pouncing proavis modelBird flightFlight is the main mode of locomotion used by most of the world's bird species. Flight assists birds while feeding, breeding and avoiding predators....
: Similar to the arboreal model, this model proposes that early predators attacked from above and evolved wings to assist in stabilizing their descent when pouncing on prey. - Wing-assisted incline running (WAIR)Bird flightFlight is the main mode of locomotion used by most of the world's bird species. Flight assists birds while feeding, breeding and avoiding predators....
: suggests that wings evolved to provide additional downward force to increase traction during fast ascent of steep slopes in chicks. - Novel association of locomotor modules: A theory introduced by Gatesy and Dial in 1996 attempts to explain how birds were capable of developing wings that eventually led to the ability of true flight. They introduce the idea of "locomotor modules" as anatomical groupings (i.e. two legs) working together as a single functional neuromuscular unit for locomotion. The authors suggest that early TheropodsTheropodaTheropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...
(evolutionary precursors to birds) began with a single locomotor module consisting of the two hind-limbs coupled with the tail. Over time, these animals developed a second locomotor module that could be independently control the fore-limbs which eventually evolved into functional wings and further decoupled tail function from the hind-limbs creating two additional modules. This decoupling allows modern birds to have the freedom to independently coordinate their three locomotor modules (wings, legs, and tails) in novel ways, thus accounting for the extreme diversity seen in the avian taxa.
Adaptation
As is true for any structure shaped by natural selectionNatural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
, bird anatomy
Bird anatomy
Bird anatomy, or the physiological structure of birds' bodies, shows many unique adaptations, mostly aiding flight. Birds have a light skeletal system and light but powerful musculature which, along with circulatory and respiratory systems capable of very high metabolic rates and oxygen supply,...
has evolved to fit a particular species' behavior and lifestyle. For example, birds that live in dense forests and require high maneuverability and precise landing capabilities tend to have wing shapes and body plans that reduce stability to allow the execution of fast turns and sudden accelerations. Seabirds, on the other hand, tend to fly for extended periods in open air because land masses are distantly separated and floating on the surface of the water can be metabolically costly due to the temperature differential between air and sea water. As a result, large sea birds rely mostly on soaring flight
Lift (soaring)
Gliding flight is heavier-than-air flight without the use of thrust. It is employed by gliding animals and by aircraft such as gliders. The most common human application of gliding flight is in sport and recreation using aircraft designed for this purpose...
because it allows these animals to achieve relatively continuous lift without the added metabolic cost of flapping their wings. Because birds fly at an angle relative to the wind during dynamic soaring
Dynamic soaring
Dynamic soaring is a flying technique used to gain energy by repeatedly crossing the boundary between air masses of significantly different velocity...
, they must be able to achieve flight speeds greater than this head wind. Consequently, birds that rely on dynamic soaring tend to have high wing loading
Wing loading
In aerodynamics, wing loading is the loaded weight of the aircraft divided by the area of the wing. The faster an aircraft flies, the more lift is produced by each unit area of wing, so a smaller wing can carry the same weight in level flight, operating at a higher wing loading. Correspondingly,...
s and high aspect ratio
Aspect ratio
The aspect ratio of a shape is the ratio of its longer dimension to its shorter dimension. It may be applied to two characteristic dimensions of a three-dimensional shape, such as the ratio of the longest and shortest axis, or for symmetrical objects that are described by just two measurements,...
s. In other words, gliding birds have wing shapes that allow them to behave more like fixed wing aircraft and rely mostly on passive gliding. Albatross
Albatross
Albatrosses, of the biological family Diomedeidae, are large seabirds allied to the procellariids, storm-petrels and diving-petrels in the order Procellariiformes . They range widely in the Southern Ocean and the North Pacific...
es have the largest wingspan of any extant bird, evidence of their primary reliance on aerodynamic and slope soaring
Ridge lift
Ridge lift is created when a wind strikes an obstacle, usually a mountain ridge or cliff, that is large and steep enough to deflect the wind upward....
techniques to achieve their extremely long migration patterns.
In contrast, thermal soaring birds, such as Rüppell's Vulture
Rüppell's Vulture
Rüppell's Vulture is a large vulture that occurs throughout the Sahel region of central Africa. The current population of 30,000 is in decline due to ongoing loss of habitat and other pressures...
s, tend to have much smaller wing loadings and aspect ratios. Because the fastest rising air occurs in the center of a thermal
Thermal
A thermal column is a column of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation, and are an example of convection. The sun warms the ground, which in turn warms the air directly above it...
, these birds optimize their flight behavior by achieving very tight turning radii
Turning radius
The turning radius or turning circle of a vehicle is the size of the smallest circular turn that the vehicle is capable of making. The term turning radius is actually a misnomer, since the size of a circle is actually its diameter, not its radius. The less ambiguous term turning circle is preferred...
. In other words, these birds tend to have smaller wings relative to body mass, which renders them less stable in gliding but gives them much more maneuverability so that they are capable of executing very tight turns.
Swimming fish
While some aquatic animals move by "walking" along the ocean floor or burrowing, the predominant mode of fish locomotionFish locomotion
The prevailing type of fish locomotion is swimming in water. In addition, some fish can "walk", i.e., move over land, burrow in mud, and glide through the air.-Swimming:Fish swim by exerting force against the surrounding water...
is swimming, achieved by exerting force on the surrounding water which, by Newton's 3rd law, results in a reactive force that propels the animal forward.
Hydrodynamic principles
Similarly to the aerodynamics of flight, powered swimming requires animals to overcome drag by producing thrust. Unlike flying, however, swimming animals do not necessarily need to actively exert high vertical forces because the effect of buoyancyBuoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
can counter the downward pull of gravity, allowing these animals to float without much effort. While there is great diversity in fish locomotion, swimming behavior can be classified into two distinct "modes" based on the body structures involved in thrust production, Median-Paired Fin (MPF) and Body-Caudal Fin (BCF). Within each of these classifications, there are a numerous specifications along a spectrum of behaviors from purely undulatory
Undulatory locomotion
Undulatory locomotion is the type of motion characterized by wave-like movement patterns that act to propel an animal forward. Examples of this type of gait include crawling in snakes, or swimming in the lamprey...
to entirely oscillatory
Oscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...
based. In undulatory swimming modes thrust is produced by wave-like movements of the propulsive structure (usually a fin or the whole body). Oscillatory modes, on the other hand, are characterized by thrust production from swiveling of the propulsive structure on an attachment point without any wave-like motion.
Median-paired fin
Many fish swim using combined behavior of their two pectoral fins or both their anal and dorsal fins. Different types of Median Paired Fin (MPF) gait can be achieved by preferentially using one fin pair over the other, and include:UNDULATORY
- RajiformRajiformRajiform swimming is a type of aquatic locomotion practiced by some fishes such as skates and rays that makes use of undulatory pectoral fin motion....
: seen in raysBatoideaBatoidea is a superorder of cartilaginous fish commonly known as rays and skates, containing more than 500 described species in thirteen families...
, skateSkateSkates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays. There are more than 200 described species in 27 genera. There are two subfamilies, Rajinae and Arhynchobatinae ....
s, and mantasManta rayThe manta ray is the largest species of the rays. The largest known specimen was more than across, with a weight of about . It ranges throughout waters of the world, typically around coral reefs...
when thrust is produced by vertical undulations along large, well developed pectoral fins. - Diodontiform: in which propulsion is achieved by propagating undulations along large pectoral fins
- AmiiformBowfinThe Bowfin, Amia calva, is the last surviving member of the order Amiiformes , and of the family Amiidae...
: undulations of a long dorsal fin while the body axis is held straight and stable - GymnotiformGymnotiformesThe Gymnotiformes are a group of teleost bony fishes commonly known as the Neotropical or South American knifefishes. They have long bodies and swim using undulations of their elongated anal fin...
: undulations of a long anal fin, essentially upside down amiiform - BalistiformZeidaeThe Zeidae are a family of large, showy, deep-bodied zeiform marine fish—the "true dories". Found in the Atlantic, Indian, and Pacific Ocean, the family contains just six species in two genera...
: both anal and dorsal fins undulate
OSCILLATORY
- TetradontiformTetraodontiformesThe Tetraodontiformes are an order of highly derived ray-finned fish, also called the Plectognathi. Sometimes these are classified as a suborder of the Perciformes...
:dorsal and anal fins are flapped as a unit, either in phase or exactly opposing one another. The ocean sunfishOcean sunfishThe ocean sunfish, Mola mola, or common mola, is the heaviest known bony fish in the world. It has an average adult weight of . The species is native to tropical and temperate waters around the globe. It resembles a fish head with a tail, and its main body is flattened laterally...
is an extreme example of this form of locomotion. - Labriform: oscillatory movements of pectoral fins and can be classified as drag based or lift based in which propulsion is generated either as a reaction to drag produced by dragging the fins through the water in a rowing motion or via lift mechanisms.
Body-caudal fin
Most fish swim by generating undulatory waves that propagate down the body through the caudal finFish anatomy
Fish anatomy is primarily governed by the physical characteristics of water, which is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does.- Body :...
. This form of undulatory locomotion
Undulatory locomotion
Undulatory locomotion is the type of motion characterized by wave-like movement patterns that act to propel an animal forward. Examples of this type of gait include crawling in snakes, or swimming in the lamprey...
is termed Body-Caudal Fin (BCF) swimming on the basis of the body structures used.
UNDULATORY
- Anguilliform: seen in eelEelEels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...
s and lampreyLampreyLampreys are a family of jawless fish, whose adults are characterized by a toothed, funnel-like sucking mouth. Translated from an admixture of Latin and Greek, lamprey means stone lickers...
s, this locomotion mode is marked by whole body in large amplitudeAmplitudeAmplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...
wavelengthWavelengthIn physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s. Both forward and backward swimming is possible in this type of BCF swimming. - Subcarangiform:similar to anguilliform swimming, but with limited amplitude anteriorAnatomical terms of locationStandard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
ly that increases as the wave propagates posteriorAnatomical terms of locationStandard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
ly, this locomotion mode is often seen in troutTroutTrout is the name for a number of species of freshwater and saltwater fish belonging to the Salmoninae subfamily of the family Salmonidae. Salmon belong to the same family as trout. Most salmon species spend almost all their lives in salt water...
. - Carangiform: body undulations are restricted to the posterior third of body length with thrust produced by a stiff caudal fin
- Thunniform: the most efficient aquatic locomotion mode with thrust being generated by lift during the lateral movements occurring in the caudal fin only. this locomotion mode has evolved under independent circumstances in teleost (ray-finned) fishTeleosteiTeleostei is one of three infraclasses in class Actinopterygii, the ray-finned fishes. This diverse group, which arose in the Triassic period, includes 20,000 extant species in about 40 orders; most living fishes are members of this group...
, sharkSharkSharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s, and marine mammalMarine mammalMarine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of...
s.
OSCILLATORY
- Ostraciiform: the body remains rigid and the stiff caudal fin is swept in a pendulumPendulumA pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position...
-like oscillation. Fish using this type of BCF locomotion, usually rely predominantly on MPF swimming modes, with ostraciiform behavior only an auxiliary behavior.
Adaptation
Similar to adaptation in avian flight, swimming behaviors in fish can be thought of as a balance of stability and maneuverability. Because BCF swimming relies on more caudal body structures that can direct powerful thrust only rearwards, this form of locomotion is particularly effective for accelerating quickly and cruising continuously. BCF swimming is, therefore, inherently stable and is often seen in fish with large migration patterns that must maximize efficiency over long periods. Propulsive forces in MPF swimming, on the other hand, are generated by multiple fins located on either side of the body that can be coordinated to execute elaborate turns. As a result, MPF swimming is well adapted for high maneuverability and is often seen in smaller fish that require elaborate escape patterns.It is important to point out that fish do not rely exclusively on one locomotor mode, but are rather lomotor "generalists," choosing among and combining behaviors from many available behavioral techniques. In fact, at slower speeds, predominantly BCF swimmers will often incorporate movement of their pectoral, anal, and dorsal fins
Fish anatomy
Fish anatomy is primarily governed by the physical characteristics of water, which is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does.- Body :...
as an additional stabilizing mechanism at slower speeds, but hold them close to their body at high speeds to improve streamlining and reducing drag. Zebrafish have even been observed to alter their locomotor behavior in response to changing hydrodynamic influences throughout growth and maturation.
In addition to adapting locomotor behavior, controlling buoyancy effects is critical for aquatic survival since aquatic ecosystem
Aquatic ecosystem
An aquatic ecosystem is an ecosystem in a body of water. Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems....
s vary greatly by depth. Fish generally control their depth by regulating the amount of gas in specialized organs that are much like balloons. By changing the amount of gas in these swim bladders, fish actively control their density. If they increase the amount of air in their swim bladder, their overall density will become less than the surrounding water, and increased upward buoyancy pressures will cause the fish to rise until they reach a depth at which they are again at equilibrium with the surrounding water. In this way, fish behave essentially as a hot air balloon does in air.
Swimming Birds
Some seabirdSeabird
Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...
species utilize surface feeding or plunge diving during foraging in which gravity and/or momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
is used to counteract buoyancy effects for a short period of time. Other species can remain submerged for longer periods of time and practice pursuit diving in which they actively produce thrust to remain submerged and chase after prey. Because birds have decoupled locomotor modules, pursuit divers can produce thrust using either their wings, feet, or some combination of the two.
Tradeoffs
Bird anatomyBird anatomy
Bird anatomy, or the physiological structure of birds' bodies, shows many unique adaptations, mostly aiding flight. Birds have a light skeletal system and light but powerful musculature which, along with circulatory and respiratory systems capable of very high metabolic rates and oxygen supply,...
is primarily adapted for efficient flight. Bird species that rely on swimming as well as flight must contend with the competing requirements of flight and swimming. Morphological characteristics that are advantageous in flight are actually detrimental to swimming performance.
Light bones:
The avian skeletal system has evolved to be extremely lightweight with hollow air spaces that are highly integrated with the respiratory system. The decreased body weight resulting from these adaptations is highly beneficial for reducing the effects of gravity, thus making lift easier to achieve. Birds that swim, however, must contend with the increased buoyancy effects of having lighter bones and a reduced body mass. Instead, diving birds increase their muscle mass, resulting in an overall increase in body mass that reduces the effects of buoyancy and makes submersion easier. This effect is predominantly seen in shallow diving birds as buoyancy effects are strongest. Higher masses in diving birds appear to be correlated with higher wing loading and consequently larger wings. Faster flying speeds also result from higher wing loading which would be potentially detrimental for small flying birds that must land precisely on small branches. Diving birds, however, do not have this constraint because open water can accommodate harder landings.
Large air spaces:
Similar to having light bones, birds also have large respiratory systems with large air spaces that reduce body weight and allow more efficient oxygen exchange required for the high metabolic demands of flight. Birds also have specialized structures called air sacs closely associated with their lungs that store air when the animal inspires, further reducing body weight and maintaining the partial pressure
Partial pressure
In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
of oxygen within the lungs equal to that of the surrounding environment. While highly beneficial for flight, decreasing body weight (and thus whole body density) increases buoyancy forces and makes maintaining submerged depth more difficult. Swimming birds have been observed to exhale before dives, reducing their air volume and thus their overall body density. Other studies have suggested than diving birds increase their blood oxygen stores thus simultaneously reducing the amount of oxygen they must retain in their lungs when diving and allowing them to dive for longer durations.
Plumage:
Bird plumage is intended to hold and deflect air to make lift easier to achieve in flight. Again, this adaptation is detrimental to swimming because the increased air volume increases buoyancy forces. Some diving birds have been observed to preen immediately before diving, and some researchers believe that this may expel the stored air and reduce the air volume, thus increasing over all body density, decreasing buoyancy effects and making submersion easier.
Behavior:
Cormorants have been observed to alter their swimming behavior with changes in body buoyancy. When body weight (and thus buoyancy) was artificially altered, horizontally swimming cormorants reduced the angle of body tilt when additional weight was added and increased the tilt angle when weight was removed. When enough weight was added to make the birds negatively buoyant, the birds angled their bodies upwards so that the thrust produced by paddling their hind-limbs acted to keep them from sinking. In other words, these birds can dynamically adjust the tilt of their bodies to adapt to changing buoyancies. Because air spaces are compressed with increased depth, diving birds must be capable of adapting to changing buoyancies throughout a dive. In fact, both Brünnich’s Guillemots and white-winged scoter
White-winged Scoter
The White-winged Scoter is a large sea duck.-Description:It is characterised by its bulky shape and large bill. This is the largest species of scoter. Females range from 950-1950 grams and 48–56 cm , averaging 1180 grams and 52.3 cm . She is brown with pale head patches...
s have been observed to alter their stroking behavior throughout a dive as an adjustment for changing buoyancies.
Lift based
Some pursuit divers rely predominantly on their wings for thrust production during swimming in addition to while in flight include aukAuk
An auk is a bird of the family Alcidae in the order Charadriiformes. Auks are superficially similar to penguins due to their black-and-white colours, their upright posture and some of their habits...
s, diving petrels, and penguin
Penguin
Penguins are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have become flippers...
s. Thrust production in these animals is produced via lift principles, much like in aerial flight. These birds essentially "fly" beneath the surface of the water. Because they have the dual role of producing thrust in both flight and swimming, wings in these animals demonstrate a compromise between the functional demands of two different fluid media.
Because the density of water is so much higher than air, the same wing excursion in either medium will produce more thrust in water. As a result, relative wing size in swimming birds tend to be smaller than comparably sized birds that fly only. Marine birds also tend to have higher than expected body mass as a mechanism to counteract buoyancy forces when submerged. The combination of smaller wings and increased body mass produce higher wing loading in these birds, consequentially resulting in faster flying speeds. While high flying speeds can be detrimental to landing on tree perches for flying birds, there is little consequence to high impact landing in water.
Birds that rely on lift based propulsion for swimming have been observed to utilize higher wing beat frequencies when flying than when submerged and swimming. This observation follows directly from the logic that the increased density of water produces greater thrust for similar wing excursions, so for a given speed fewer wing beats are needed to create identical propulsion totals. It is also suggested that lift based swimmers have higher swim speeds and greater metabolic efficiency than drag based swimmers because they are able to displace greater water volumes (thus experiencing greater reactive thrust) with their wings than a comparable sized bird can with its feet.
Drag based
By taking advantage of the fact that birds can freely associate any of their three locomotor modules, some pursuit divers rely predominantly on their webbed hind-limbs for thrust production during swimming and isolate wing function to aerial flight. Drag-based pursuit divers include cormorantCormorant
The bird family Phalacrocoracidae is represented by some 40 species of cormorants and shags. Several different classifications of the family have been proposed recently, and the number of genera is disputed.- Names :...
s, greebe
Weepul
The weepul is a small, spherical, fluffy toy, with large, plastic googly eyes, and no limbs. Weepuls come in various colors...
s, loon
Loon
The loons or divers are a group of aquatic birds found in many parts of North America and northern Eurasia...
s, and some duck
Duck
Duck is the common name for a large number of species in the Anatidae family of birds, which also includes swans and geese. The ducks are divided among several subfamilies in the Anatidae family; they do not represent a monophyletic group but a form taxon, since swans and geese are not considered...
species. Like patterns seen in fish, drag based avian swimmers are more maneuverable than their lift based counterparts. As a result, drag based swimming mechanisms are more often seen in birds that live in estuarine
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
environments with more environmental obstacles that must be avoided.
Some swimming birds have been observed to utilize different propulsive mechanisms in different phases of a dive. Drag based swimming is most often observed in swimming birds during the foraging (or bottom) phase of a dive because it provides greater maneuverability for pursuing prey while the more efficient lift based swimming mechanisms are used during descent. Guillemot
Guillemot
Guillemots is the common name for several species of seabird in the auk family . In British use, the term comprises two genera: Uria and Cepphus. In North America the Uria species are called "murres" and only the Cepphus species are called "guillemots"...
s were observed to use lift based swimming intermittently during the ascent phase of a dive but rely mostly on passive buoyancy forces to lift them to the surface.
Flightless Avian Swimmers
Some examples of birds who have lost the ability to fly in favor of an aquatic lifestyle include:- PenguinPenguinPenguins are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have become flippers...
s: one of the most highly adapted birds for swimming, penguins swim via lift produced by their wings and demonstrate a highly streamlined body shape that reduces drag. - Flightless CormorantFlightless CormorantThe Flightless Cormorant , also known as the Galapagos Cormorant, is a cormorant native to the Galapagos Islands, and an example of the highly unusual fauna there. It is unique in that it is the only cormorant that has lost the ability to fly...
s: have very small wings incapable of producing enough lift for flight, and swim via drag based paddling of their webbed hind limbs - Magellanic Flightless Steamer Duck
- Falkland Flightless Steamer Duck
- White-headed Flightless Steamer Duck
- Auckland Island TealAuckland Islands TealThe Auckland Teal or Auckland Islands Teal is a species of dabbling duck of the genus Anas that is endemic to Auckland Islands south of New Zealand. The species was once found throughout the Auckland Islands but is now restricted to the islands that lack introduced predators; Adams Island, Enderby...
- Campbell Island TealCampbell Island TealThe Campbell Teal or Campbell Island Teal is a small, flightless, nocturnal species of dabbling duck of the genus Anas endemic to the Campbell Island group of New Zealand. It is sometimes considered conspecific with the Brown Teal...
- Great AukGreat AukThe Great Auk, Pinguinus impennis, formerly of the genus Alca, was a large, flightless alcid that became extinct in the mid-19th century. It was the only modern species in the genus Pinguinus, a group of birds that formerly included one other species of flightless giant auk from the Atlantic Ocean...
- Mancalla
- HesperornithesHesperornithesHesperornithes is an extinct and highly specialized clade of Cretaceous toothed birds. Hesperornithine birds, apparently limited to former aquatic habitats in the Northern Hemisphere, include genera such as Hesperornis, Parahesperornis, Baptornis, Enaliornis, and probably Potamornis, all...
Flying fish
The transition of predominantly swimming locomotion directly to flight has evolved in a single family of marine fish called Exocoetidae. Flying fish are not true fliers in the sense that they do not execute powered flight. Instead, these species glide directly over the surface of the ocean water without ever flapping their "wings." Flying fish have evolved abnormally large pectoral fins that act as airfoils and provide lift when the fish launches itself out of the water. Additional forward thrust and steering forces are created by dipping the hypocaudal (i.e. bottom) lobe of their caudal fin into the water and vibrating it very quickly, in contrast to diving birds in which these forces are produced by the same locomotor module used for propulsion. Of the 64 extant species of flying fish, only two distinct body plans exist, each of which optimizes two different behaviors.Tradeoffs
Tail Structure:While most fish have caudal fins with evenly sized lobes (i.e. homocaudal), flying fish have an enlarged ventral
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
lobe (i.e. hypocaudal) which facilitates dipping only a portion of the tail back onto the water for additional thrust production and steering.
Larger mass:
Because flying fish are primarily aquatic animals, their body density must be close to that of water for buoyancy stability. This primary requirement for swimming, however, means that flying fish are heavier than other habitual fliers, resulting in higher wing loading and lift to drag ratios for flying fish compared to a comparably sized bird. Differences in wing area, wing span, wing loading, and aspect ratio have been used to classify flying fish into two distinct classifications based on these different aerodynamic designs.
Biplane body plan
In the biplaneBiplane
A biplane is a fixed-wing aircraft with two superimposed main wings. The Wright brothers' Wright Flyer used a biplane design, as did most aircraft in the early years of aviation. While a biplane wing structure has a structural advantage, it produces more drag than a similar monoplane wing...
or Cypselurus'
Cypselurus
Cypselurus is a genus of flyingfishes in the family Exocoetidae.-Species:* Genus Cypselurus** Narrowhead flyingfish, Cypselurus angusticeps Nichols & Breder, 1935** Ornamented flyingfish, Cypselurus callopterus...
' body plan, both the pectoral and pelvic fins are enlarged to provide lift during flight. These fish also tend to have "flatter" bodies which increase the total lift producing area thus allowing them to "hang" in the air better than more streamlined shapes. As a result of this high lift production, these fish are excellent gliders and are well adapted for maximizing flight distance and duration.
Comparatively, Cypselurus
Cypselurus
Cypselurus is a genus of flyingfishes in the family Exocoetidae.-Species:* Genus Cypselurus** Narrowhead flyingfish, Cypselurus angusticeps Nichols & Breder, 1935** Ornamented flyingfish, Cypselurus callopterus...
flying fish have lower wing loading and smaller aspect ratios (i.e. broader wings) than their Exocoetus monoplane counterparts, which contributes to their ability to fly for longer distances than fish with this alternative body plan. Flying fish with the biplane design take advantage of their high lift production abilities when launching from the water by utilizing a "taxiing glide"
Taxiing
Taxiing refers to the movement of an aircraft on the ground, under its own power, in contrast to towing or push-back where the aircraft is moved by a tug...
in which the hypocaudal lobe remains in the water to generate thrust even after the trunk clears the water's surface and the wings are opened with a small angle of attack for lift generation.
Monoplane body plan
In the Exocoetus or monoplaneMonoplane
A monoplane is a fixed-wing aircraft with one main set of wing surfaces, in contrast to a biplane or triplane. Since the late 1930s it has been the most common form for a fixed wing aircraft.-Types of monoplane:...
body plan, only the pectoral fins are enlarged to provide lift. Fish with this body plan tend to have a more streamlined body, higher aspect ratio
Aspect ratio
The aspect ratio of a shape is the ratio of its longer dimension to its shorter dimension. It may be applied to two characteristic dimensions of a three-dimensional shape, such as the ratio of the longest and shortest axis, or for symmetrical objects that are described by just two measurements,...
s (long, narrow wings), and higher wing loading than fish with the biplane body plan, making these fish well adapted for higher flying speeds. Flying fish with a monoplane body plan demonstrate different launching behaviors from their biplane counterparts. Instead of extending their duration of trust production, monoplane fish launch from the water at high speeds at a large angle of attack (sometimes up to 45 degrees). In this way, monoplane fish are taking advantage of their adaptation for high flight speed, while fish with biplane designs exploit their lift production abilities during takeoff.
See also
- Fish locomotionFish locomotionThe prevailing type of fish locomotion is swimming in water. In addition, some fish can "walk", i.e., move over land, burrow in mud, and glide through the air.-Swimming:Fish swim by exerting force against the surrounding water...
- Bird flightBird flightFlight is the main mode of locomotion used by most of the world's bird species. Flight assists birds while feeding, breeding and avoiding predators....
- Flying Fish
- AukAukAn auk is a bird of the family Alcidae in the order Charadriiformes. Auks are superficially similar to penguins due to their black-and-white colours, their upright posture and some of their habits...
- Fluid dynamicsFluid dynamicsIn physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow—the natural science of fluids in motion. It has several subdisciplines itself, including aerodynamics and hydrodynamics...
Recommended reading
Alexander, R. McNeill (2003) Principles of Animal Locomotion. Princeton University Press, Princeton, N.J. ISBN 0-691-08678-8Vogel, Steven (1994) "Life in Moving Fluid: The Physical Biology of Flow." Princeton University Press, Princeton, N.J. ISBN 0-691-02616-5 (SEE particularly pp115–117 and pp207–216 for specific biological examples swimming and flying respectively)
Wu, Theodore, Y.-T., Brokaw, Charles J., Brennen, Christopher, Eds. (1975) "Swimming and Flying in Nature: Volume 2.: Plenum Press, New York, N.Y. ISBN 0-306-37089-1 (SEE particularly pp615–652 for an in depth look at fish swimming and pp845–867 for a detailed analysis of vertebrate flight)
External links
- Lab website for Dr. JR Lovvorn who investigates locomotion characteristics of diving birds
- Lab website for Dr. Matt McHenry who researches hydrodynamics of swimming at low Reynold's numbers
- Liquid Life Laboratory of Dr. Frank Fish who studies swimming in marine mammals
- Basic introduction to the basic principles of biologically inspired swimming robots
- Research for this Wikipedia entry was conducted as a part of a Locomotion Neuromechanics course (APPH 6232) offered in the School of Applied Physiology at Georgia Tech