As can be seen in the chart, CR is no more limited in birds than in other classes, but its distribution drifts, leaving the alternating asymmetrical column blank, and appearing more in the mixed column.
Alternate symmetrical gait is not present in birds</W>with one exception</W>as the wings are immobile during walking because the CR flexed resting position of the forelimbs allows no movement. However, quite suprisingly, penguins tobaggoning
, or sliding on their stomachs, propel themselves with wings and legs moving in the altenate symmetrical mode, exactly as in mammals or reptiles. Obviously, this mode is latent in avian kinematics.
The Alternate asymmetric mode almost unviersally applies to birds waking at a slow to moderate pace. Due to extreme flight or aquatic specializations some hummingbirds, swallows, etc., or grebes and waterfowl cannot walk well or at all (cf. Dial / A
uk...). Small perching birds in the Passeriform order prefer to hop rather than walk because it offers faster movement than the alternate gait at the relatively small size of their stride. Conversely, long-legged aquatic birds walk and run and rarely hop at
normal or fast rates of movement (except in display). Birds also engage in lateral walking on branches. Treading in water, as practiced by grebes in their so-called "weed dance" is a manner of walking in place. (?O^O)
Parallel symmetry appears in jumping, hopping or in aggressive clawing (etc.?) and in specail actions like prey capture by the raptor birds in the air (eagles, hawk, etc.), on the ground (eagles, owls, etc.) or at the water surface (fishing eagles),
as the clawed feet are shot out and the wings flap down. Although larger birds such as eagles can hop, general use of this behavior in terrestrial locomotion is reserved for small "hopping" birds.
Parallel asymmetry is the mode of flight, where only the forelimbs generate propulsion. Penguins and auks? fly under water with the same parallel strokes as in flight.
The mixed mode, unlike in other classes, is a more common behavior in birds. Parallel wing flapping combined with alternating leg motion,arises in display and in the running takeoff by certain birds. However, display is not locomotion, but a form of
localized body movement. As for the running takeoff practiced by some. but not all long-legged aquatic birds, like flamingoes and certain herons, and similar species, as well as typically by game birds, like grouse, pheasant, turkey, jungle fowl, etc., onc
e again, this running sequence is not primarily a device of locomotion, but only an intermediary (speed increasing) act between walking and flying. It arises due to necessities most likely imposed by anatomy and size. As will be demonstrated, the mixed mode
is a highly ineffective action of body transport, and hence it is not found in efficient locomotion by any animal. It is imorteant to note that the mixed mode does not occur in the locomotion of any pther vertebrate classes. Its only non-avian manfestation
is perhaps among fish (fanning?) and in mole excavation through an extremely dense medium.
These points effectively reduce the significance of the mixed mode in avian locomotion and will be taken up again when discussing the early cursorial theories of bird flight.
The clasification for birds follows the system of .... cite source!!!!