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University Microfilms International 300 N. ZEEB ROAD. ANN ARBOR. Ml 48106 18 BEDFORD ROW. LONDON WC1R 4EJ, ENGLAND 8001783
M e s s in g e r, D a v id S t e v e n
MECHANICS OF WALKING AND SWIMMING OF THE DUCK ANAS PLATYRHYNCHOS
The Ohio State University Ph.D. 1979
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University Micnjfilms international
300 N. 2 E E 3 RD.. ANN ARBOR. Ml 48106 1313) 761-4700 MECHANICS OF
WALKING AND SWIMMING OF THE DUCK
ANAS PLATYRHYNCHOS
DISSERTATION
Presented in Partial Fulfillment of the Requirement for
the Degree Doctor of Philosophy in the Graduate
School of The Ohio State University
by
David Steven Messinger, B.S., M.S., M.S.
Vc ->V - k 4c -k
The Ohio State University
1979
Reading Committee: Approved By
Dr. Abbot S. Gaunt
Dr. George H. Dalrymple
Dr. Roy A. Tassava
Dr. Walter G. Venzke Advisor ACKNOWLEDGMENTS
I am grateful to Dr. Abbot S. Gaunt for the oppor
tunity to pursue this study in his laboratory. Dr. G.
Dalrymple and Dr. R. Tassava offered encouragment and
helpful suggestions. I am indebted to Dr. J. Munford,
Mr. and Mrs. Clapp, M. Dautorus and M. Anderson, for
their able assistance during my experiments.
I thank Mr. A. Macias for the use of his photographic
expertise. Many technical problems were resolved through
the assistance of Dr. F. Heft. Dr. S. Weber provided
valuable assistance in the preparation of the manuscript.
Without the encouragement of Mr. G. Cronin, Dr. J.
Hostettler, Dr. W. Butts, Dr. L. Sohaki and Dr. W. Wilson,
Dr. G. Goslow and Mrs. Vedder this study would never have
been attempted.
Support came from the Ohio State Department of Zoology
the Josyln Van Tyne Memorial Fund, and the Frank M. Chapman
Award from the American Museum of Natural History. Addi-
' tional support was provided through National Science Founda
tion grants GB40069 under Dr. A.S. Gaunt and RF4074A1 under
Dr. R. McGhee. VITA
February 13, 1950...... Born - Amityville, New York
1972 ...... B.S. State University of New York, Oneonta
1974 ...... M.S. Northern Arizona University, Flagstaff, Arizona
1977 ...... M.S. The Ohio State University, Columbus, Ohio
1978-1979...... Teacher, Columbus Public Schools
PUBLICATIONS
"Ankle Extensor Activity in the Walking Cat." Amer. Zool. 14:1267 Abstract, 1974
FIELD OF STUDY
Major Field: Zoology, Anatomy, Physiology
Studies in Animal Locomotion. Professor George E. Goslow, Jr.
Studies in Animal Locomotion. Professor Abbot S. Gaunt TABLE OF CONTENTS
Page
ACKNOWLEDGMENTS...... ii
VITA...... iii
LIST OF FIGURES...... vi
LIST OF PLATES...... vn
INTRODUCTION...... 3
Chapter
I. MATERIAL AND METHODS...... 14
Animals...... 14
Recording Techniques...... 15
Observation Methods: Walking...... 19
Observation Methods: Swimming...... 21
Analytical Methods...... 23
Stereo Viewing...... 23
Stick Figures...... 27
II. RESULTS...... 29
Walking: Knee, Ankle and Foot Angles 29
Walking: Front and Rear Views...... 32 iv Page
Swimming: Knee, Ankle and Foot Angles.... 33
III. DISCUSSION...... 35
Comparison of the Joint Angles During Walking and Swimming...... 35
Walking and Swimming Compared...... 39
Comparison of the Intertarsal (Ankle) Angles of the Walking Duck, Pigeon and Gull...... 43
IV. CONCLUSIONS...... 47
V. FURTHER INVESTIGATIONS...... 49
VI. BIBLIOGRAPHY...... 50
VII. APPENDIX...... 53
v LIST OF FIGURES
Figure Page
1. Walkway for Observing Ducks Walking...... 53
2. Tank for Observing Ducks Swimming...... 54
3. Diagram of Duck's Leg with Joint References... 55
4. Stick Diagrams of the Walking Duck...... 56
5. Stick Diagrams of the Swimming Duck...... 58
6 . Graph of Knee, Ankle and Foot Angles 60 During the Walk Cycle (Graph #1)......
7. Graph of Knee, Ankle and Foot Angles During the Swim Cycle (Graph #2)...... 61
8 . Graph Comparing Knee Angles of the Walking and Swimming Duck (Graph #3) ...... 62
9. Graph Comparing Ankle Angles of the Walking and Swimming Duck (Graph # 4 ) ...... 63
10. Graph Comparing Foot Angles of the Walking and Swimming Duck (Graph #5)...... 64
11. Graph Comparing Ankle Angles of the Walking Duck, Pigeon, and Gull (Graph # 6 )...... 65
vi LIST OF PLATES
Plates Page
I. Rear and Lateral Views of Walking with Lateral Views of Swimming...... 66
II. Rear View of Walk with Lateral View of Swim...... 68
III. Lateral View of the Walk...... 70
IV. Moderately Fast Swim...... 72
V. Closeups and Multiple Exposures of the Walking Duck...... 74
VI. Frontal and Lateral Views of the Walk...... 76
VII. Fast and Slow Swimming...... 78 ABSTRACT
The mallard duck, Anas platyrhynchos was studied to compare its walking and swimming movements. Special equip ment was constructed so that the subjects could be observed under conditions which would insure that the movements recorded would represent the animal in a near natural state
Video recordings were found to be the most appropriate means of studying the fast locomotor actions of walking and swimming ducks. Conventional techniques were modified through the use of lighting by a xenon flash as described within this report.
The data collected during this investigation were analyzed using a new method which allows the viewer to see the photographic images in such a way that they appear to b three dimensional. This is a new technique that presently provides only qualitative rather than quantitative data.,
For this reason, more conventional stick figures were made from tracings made from photographs of the original video tape recordings. Measurements were made of the knee, ankle and foot angles from which graphs were made.
The movements of each joint are described, and all the angular displacements of the joints compared with each other. Relationships are described and explained. 2
During the walk cycle it was found that the knee and ankle move synchronously while the foot (intertarsal) angle behaves completely out of phase. The same was found true for the swimming duck.
It was found that the swimming duck has a knee that remains at a relatively fixed position during slow swimming.
The range of motion of the knee can however, be seen to increase with speed. Again, the foot and ankle angles when graphed prove to have curves that appear as mirror images of one another. These joints appear to be behaving almost 180° out of phase.
Differences in the movements of walking and swimming are explained as being the result of adaptations by the duck to the physical characteristics of the respective media involved. Of prime importance are those adaptations made to allow the animal to cope with the factors of weight
(on land) and drag (in water).
It is concluded that the similarities present in the movements of the walking and swimming duck can best be explained as being the result of the modification through time of a basic pattern of walking movements to meet the challenge of the aquatic medium. Comparisons made with data from the literature for other aquatic and cursorial birds indicate that these assumptions are valid in a variety of cases. INTRODUCTION
Birds have adapted to several different types of loco motion. Various birds walk, hop, run, swim, and fly.
Perhaps because man can do all of these activities except
fly, he has centered most of his attention on the flight of birds. Whereas, the forelimbs of birds have been studied
in an attempt to understand their function, the hindlimbs have been examined mainly by taxonomists who have attempted
to use their structure to study evolutionary relationships
(see George and Berger 1966 for a review). Taxonomists have
paid little attention to the functional aspects of the avian
locomotor system. Only recently have functional morpholo-
gists begun to examine the dynamic qualities of the loco motor systems in living birds.
Most previous studies were based on data collected from dissections of dead animals, rather than from observations made of living animals. Those descriptions that are avail
able are few and usually qualitative in nature. Until recently few recordings and measurements were made of nofl
flying birds.
The list of taxonomically oriented papers that deal with the avian hindlimb is enormous and beyond the scope of
this paper. The following papers are mentioned to give the reader a familiarity with the kinds of studies that have been conducted in the past. The questions asked in these studies are, for the most part, limited in scope, as are the investigative techniques. 5
Over the preceding decades, a great deal of data regard
ing avian locomotion has been collected by many people.
Early investigators were limited by the technology available
at the time. Functional anatomical and physiological tech
niques have improved swiftly in recent years. Modern elec
tronics and high speed photography as well as other record
ing techniques have opened new vistas to those scientists
who dream of understanding the subtleties of the locomotor
systems of organisms. The rewards for the investigator who
pursues this field of inquiry will be the personal satisfac
tion of providing data which other scientists will be able
to base their studies upon.
The avian locomotor system is particularly interesting
in that it addresses the problem of bipedalism. Bipedalism
is a phenomenon peculiar to mammals, reptiles and birds.
Bipedalism in man has been studied rather extensively for
evolutionary and clinical reasons. This paper will not
address itself to comparisons between bipedalism in man and
other organisms. One basic reason lies in that man is a
plantigrade animal whereas birds are digitigrade. While
the mode of locomotion is similar, the structures involved
' perform analogous roles not particularly appropriate to the
questions that will be asked here. The selective pressures
responsible for the adoption of bipedalism by man, birds,
and reptiles are very different. Three impetuses for the
adoption of a bipedal gait have been suggested: 1 ) for speed in the case of the reptiles; 2 ) for freeing of the fore
limbs for manipulations and feeding as in man, and 3) the
adaptation of the forelimbs for flight as in birds. A more
detailed discussion is given by DuBrul (1962).
One of the first functional studies of bird locomotion
relevant to this paper was by Stolpe in 1932. Stolpe in
vestigated avian aquatic locomotion and related his obser
vations to the function of the leg. He discusses the adap
tations of the hind limb for birds that live in a variety
of habitats. His work is significant in that it attempts
to explain the acquisition of a function in terms of the
environmental pressures with which this function allows the
animal to cope.
Miller (1937) studied the Hawaiian Goose, a terrestri
ally adapted bird. He describes the gait of this goose
from unaided observations and some simple snapshots. His
work illustrates some of the technical limitations under
which these men had to work and includes the wet volumes of
the goose's leg muscles along with their descriptions.
Miller's paper shows a classical approach to the study of
form and function in that he is primarily concerned with
' taxonomic questions.
In 1946, Fisher, recognizing the importance innerva
tion has in the study of homologies, published information
regarding both the muscles and the nerves that supply them.
He was aware that though muscles may shift position and 7
function, the nerves that supply them may not (see
Hildebrand, 1974 for a discussion). He therefore included
this information in his descriptions of the wing and leg
muscles of cathartid vultures.
Other taxonomic studies on birds were conducted by
Burt (1930), on woodpeckers, and by Richardson (1942) who
studied modifications for tree trunk foraging in birds that
are unrelated. Richardson shows excellent insight into the
rationale behind functional studies, and his thoughts will
be commented upon later in this paper.
Wilcox, (1952) did a taxonomical study on another
aquatic bird, the loon. Berger (1953) worked with cuckoos,
and Hartman (1961) examined the wet weights of leg muscles
of some birds. Both employed dissection techniques and did
not perform any experiments on living birds.
In 1967, Owre watched the anhinga and the cormorant,
both aquatic birds that dive, and reported his observations.
He used no underwater recording techniques, so no data are
available for the scrutiny of the reader.
Dissections provided most of the data for these early
studies. It was not until 1965 that Spring employed cinema
tography, X-ray, photography, and dissections to make func
tional anatomical observations. Spring studied the climb
ing and pecking adaptations of some woodpeckers.
Raikow (1970) described both aquatic and terrestrial
locomotion in three species of ducks. The mallard was one of the ducks he studied and his observations were important
starting points for this paper. In his rather taxonomic
study, he describes the swimming movements of ducks that he
watched swim in a lake or marina. No recordings were made
of these movements, so his findings are subject to verifica
tion. Raikow describes the legs of a swimming duck as being
held in an abducted position, the degree of which is charac
teristic of the species being observed. His description of
walking is cursory and brief.
More recently, Rylander and Bolen (1974) investigated
the structures associated with walking, swimming and feed
ing of three species of whistling ducks (Dendrocygnae).
They used cinematography to describe the gaits of these
ducks. They then made taxonomic conclusions as to the rela
tion between these species.
Prang and Schmidt-Nielson (1970), while measuring the
energetic cost of swimming in ducks, made measurements of
swimming speeds and briefly commented on the duck’s stroke
as it relates to the bird’s speed. More will be said of
their paper in the discussion section.
In 1971, Cracraft examined several interesting aspects
' of the avian locomotor system with specific reference to
the common pigeon (Columba livia). He examined the major
morphological features of the leg joints using modern tech
niques of gross anatomy and microscopy and followed these
observations by a description of the hind limb muscles. 9
The fiber lengths and arrangements, attachments, angles of pinnation, and the histology of the muscles were also dis
cussed. These finds were treated in a classical manner in
that they are mostly descriptive in nature. It is in the
latter section of Cracraft's paper that his work begins to
gain stature, and becomes more than just a collection of data. Cracraft presents a high speed motion picture analy
sis of the pigeon's gait as it performs a slow walk, moder
ate walk and a run. In this section, Cracraft discusses
the angular displacements of the joints and their angular
velocities. Some of the characteristics of landing are
also mentioned.
Cracraft assembles his data to construct an activity
sequence for the muscles used by the pigeon in locomoting.
This is an interesting attempt at using information gained
from non-living specimens to make definite statements re
garding the muscular actions as they may be occuring in
live birds. Although his conclusions are logical, based on
his data and assumptions, the validity of his conclusions
are certainly subject to question and further experimental
investigation. The results of an electromyographic analysis
of the hind limb musculature of the pigeon will someday
confirm or dispute Cracraft's conclusions as to the func
tions of these muscles in a living pigeon. Nonetheless,
Cracraft's paper gives us some good data for making more
comparisons. 10
Dagg (1977) provides us with more data with which we
may compare the locomotor activity of many more birds. In
her study of the Silver Gull, Dagg filmed and examined the
angles made by the tibiotarsal-tarsometatarsal joint of
each leg during walking. The angles were then correlated
with the bird's speed. An attempt is made to find a rela
tionship between the speed of a step with the size of the
bird being studied. Head bobbing as exhibited by some birds
and not others is also commented on though the conclusions
are not definite. Dagg also comments on hopping, a form of
bipedalism used by some birds. In addition to work done on
the Silver Gull, 24 other species of small and large birds
were examined as to their gaits. The data are not very
detailed, yet allow us to make comparisons with the pigeon
and the duck.
Clarke and Alexander in 1975 did an elegant analysis
of the forces involved in running by the quail. They com
ment on the locomotor process in terms of the physicist.
Their data provide little information of use to this paper
in regards to determining leg movements. However, their
observations do provide useful information from which I
'will draw some conclusions.
It can be seen that early studies usually attempted to
compare the morphological features of several species in an
attempt to draw evolutionary and taxonomic conclusions.
More recently single species studies have become popular. 11
In single species studies, the characteristics of a given animal as it locomotes are studied in detail. Conclusions are then made as to the relationship between the observed morphological features and the functions they perform. The result of all the previous studies is that we now have a considerable amount of data from which we may make new comparisons.
In this study, interspecific and intraspecific com parisons were made. The common wild type mallard duck,
(Anas platyrhynchos) was studied as it walked and swam.
Comparisons were also made between the data presented in the paper and the data presented in the literature.
Richardson (1942) discussed the basic rationale behind most functional anatomical studies. He stated:
Functional anatomical studies may deal with just one kind of animal, but ordinarily several forms are compared. Such comparisons offer a convenient and necessary check on interpretation and disclose the evolutionary significance of the specialized struc tures. In general, there are two types of comparative functional-anatomical studies: one of the closely related forms, the other of distantly related forms. The first type leads to an understanding of the phylogeny of a well-circumscribed group or of the evolution of its adaptations. This is most often accomplished by analyzing varying degrees of the same adaptations in the related forms... In the study of distantly related animals, one of the chief aims is to establish the validity of qualitative and obvious adaptations by showing their occurrence in unrelated species of the same habits. This is essentially a consideration of convergent or of parallel adaptation.
Another interesting case exists. We may also compare distantly related species that do not share common ecologi cal characteristics. If we should find, despite these large 12
differences in habits and morphology, that the species still
maintain strong functional similarities, then we may con
clude that the selective advantage granted the animal by
the original adaptation was, and is, so strong that modifi
cations of the basic pattern have been selected against.
Species do evolve, and birds have adapted to many
different factors. In order to maintain a given function,
such as a gait, despite other morphological changes in say
the neuromuscular or skeletal system, we must imagine that
the entire complex is relatively flexible: that is, it will
adapt to changing conditions over a long period of time.
On the other hand, once a pattern is established, as biped
alism has been established long before birds that swim
evolved, the conservative nature of the nervous system
would tend to maintain the original patterns of movement.
For these reasons I believe that differences in movements
within a species or between species will be relatively
slight, or at least modifications of a basic pattern.
Two ways of testing this thesis come to mind. First,
one can take an animal such as the duck that is adapted to
two media and examine its movements in each. Whether swim-
^ming or walking, the duck must use the same morphological
components. We are comparing the duck with itself, so in a
sense, it becomes its own constant. By changing the media
in which it locomotes from land to water and back, we are
forcing the same anatomical and physiological systems to 13 operate under different conditions. We can thus expect to gain some insight into the relative plasticity of the system.
Another approach is to take the first animal, the duck, and compare it with other birds. Birds can be chosen that are entirely terrestrial, or have adapted to swimming in varying degrees. Using the data supplied by the literature, especially that provided by Dagg and Cracraft, I will test the thesis that the basic locomotor pattern is so entrenched in the avian line that only slight modifications of the basic pattern will be found. MATERIALS AND METHODS
Animals
The early phases of this study consisted of visual and
photographic observations of domesticated white ducks.
Various techniques were employed in an attempt to find a method of recording and analyzing both walking and swimming.
At the same time, both newly hatched ducklings and adult ducks were used as subjects in an attempt to discern whether young ducklings would prove a more convenient animal to
study. It was hoped that ducklings could be used because of their small size and minimal food requirements and would not tax the spacial or monetary resources of our laboratory.
The ducklings were not used in the final analysis; they were too fragile. Final data collections were made using
six adult male wild type mallards (Anas platyrhynchos) obtained from a local propagator. These animals were pin
ioned, which did not change their behavior in any way.
Only male ducks were used because they survived caging better than females and no discernable differences could be detected in regards to the locomotor behaviors of the
two sexes.
14 15
Recording techniques
Initially 16mm films at 32 frames per second (fps) were made of the original dozen ducklings and ten adults.
Some still 35mm photographs were taken of some adult ducks utilizing a xenon flash. Both of these recording methods were abandoned for several reasons.
Motion pictures proved too inconvenient, time consum ing, and costly. The images that resulted from this method did not give sufficient resolution, and several days would elapse between the time of exposure and final development.
Perhaps the most inconvenient aspect of conventional motion picture photography is the lack of any immediate means to monitor the quality of the data collected. If a sequence was not taken correctly or if there was a mistake made at the developing laboratory, days would elapse before the error or oversight could be rectified. Such delay was a serious drawback because one had to consider the set-up time consumed for a session and the scheduling of need assistants.
Nor were the resulting photographic images of suffi cient quality, because 32 fps was not fast enought to stop the movements of the lower leg. Even Cracraft who filmed the pigeon at 250 fps reported that he could not adequately discern the rapid movement of the phalanges. Synchronizing a stroboscope to the camera may have eliminated the blur ring problem, but the aforementioned delay was a problem 16 large enough that I decided against investing in this technique.
The cost of film and developing were also prohibiting factors. Ducks were found to be less than ideal subjects.
Many attempts were made to acquire just one useful sequence of movements due to the stubborn nature of the animals.
Great quantities of film would have had to be exposed be fore the desired data could have been collected.
Another handicap inherent to conventional 16mm cinema tography is lighting. To achieve maximum clarity and depth of field, it is desireable to use small aperture, but the bright (hot) lamps required for this posed two problems.
First, the lights disturbed the subjects. Second, the animals quickly overheated in the hot light during walking experiments, showing clear signs of distress from the heat in a very short time.
Also found to be unsatisfactory were 35mm still photo graphs. Though the images obtained by using a short dura tion xenon flash were sharp, they gave only isolated frag ments of data from the series of movements responsible for the act of locomoting.
Video recording offered a solution to some of the above problems. Video tapes can be played back instantly elimi nating long and costly developing times. The tapes can also be erased and reused; only useful data need be saved.
With conventional motion picture methods you pay for your mistakes. Television cameras also allow continuous monitor ing during recording. This provides immediate feedback as to what is going onto the tapes. In addition, the sound track can be used for verbal notes and comments. Electro- physiological data may also be recorded in synchrony with the visual image providing an opportunity to use electro- mygraphy, electrocardiography or any other from of electro- physiological. Attempts were made to use these techniques, but they will not be considered. The main drawback to con ventional video recording is the lack of resolution of the images.
In black and white television cameras, the visual image is retained on a phosphorescent screen for a rela tively long period even after the electron beam has swept across the screen to change the light image into electrical impulses. The retention time inherent to the phosphors causes blurring of the image when the tape is played back at slow speeds. Fortunately a new technique was developed to overcome this problem.
Ordinarily, a television camera is used with contin uous lighting. The image that is focused on the vidicon tube's phoshorescent surface, unless stationary, moves along the screen's surface. Because of the long retention time of the vidicon tube's coating, when the electron beam
sweeps back for the next image, it not only sees the image of the subject in its new position, it also transmits the 18 previous "ghosts" image. The electron beam scans the image tube thirty times per second. As in the case of cine films, the illusion of motion is a product of our tendency to re tain visual images and blend them into what we interpret as one smooth continuous movement if the images are presented about the human fusion frequency of 10 fps.
Photographers have known for years that image blurring can be eliminated by using the light from a bright discon tinuous light source such as that from a spark or xenon flash tube. This technique I discovered also works when applied to video records, and greatly enchances its capabilities.
The light from a xenon stroboscope served this purpose.
The stroboscope was set for a flash rate of 1800 flashes per minute (fpm). In this way only one brief flash of light was emitted every 33.33 milliseconds (ms) (thirty times per second) . The television vidicon tube "saxv" noth ing in between flashes. Therefore after an image was formed on the screen, the electron beam was then scanning it during a period of darkness. Only the position of the subject during the very brief period for which the light was on was recorded on the screen. By the time the light flashed again, the original image had some time to decay, and the subject moved to a new position. Ghosts are still visible, yet now they consist of distinct images at regular inter vals. Instead of detracting from the data they enhance it. 19
They allow one to see the limb in several positions at
regular time intervals on the same frame.
The camera and light source were not synchronized as
the technical complexity of this procedure was prohibitive.
Fortunately the brief duration of the flash (less than
.0005 seconds) gives one a relatively long period of time
per frame in which to provide the flash for the next sweep
of the vidicon tube's electron beam. Occasionally the
timing of the two events was such that the resulting images
were not as bright as one would wish. This would occur if
the electron beam were to sweep the screen long after the
stroboscope had already flashed.
Observation methods; walking
I discovered early in my experiments that ducks could
not be expected to behave in a predictable manner suitable
for my purposes. The animals never become tame despite
frequent handling. Some remained relatively vicious, and I
learned that the wings, claws, and bill of an enraged or
frightened duck are formidable weapons. A fleeing duck is
very elusive and can cause considerable destruction.
Walking movements were monitored using a custom build
'walkway consisting of a 121.92 cm by 182.88 cm fibreboard
back wall, a 30.48 cm wide pine walking surface, and a
121.92 cm by 182.88 cm clear plexiglass observation window
which served as the front wall (see Figure 1). Recordings
could be made from the front, back and side. The animals 20
were controlled by an assistant from behind the opaque back
wall. An unwilling subject could be reached from above
since the two walls (front and back) were braced by simple
notched braces which were small, movable and removable.
The dimensions allowed the duck freedom of movement only
within the bounds prescribed by the dimensions of the
walkway.
The walkway's length was determined by several factors.
Spacial restrictions dictated that the walkway be mobile.
The walkway had to be long enough so that the subject could
be taped after it had "warmed up" with a few steps. I
wanted to record animals moving at a constant velocity.
It was decided that the camera remain fixed while the
subject passed through its field of view. Moving the cam
era to follow the subject would have introduced other vari
ables. For instance, to keep the subject at a constant
distance from the camera, a curved pathway would have been
needed, and the camera would have been placed at the focus
of the curve. This would, however, require the duck to
constantly accelerate due to the continuous directional
changes it would have to make to remain on the walkway. To
'minimize this effect, a curve with a very large radius,
with a very gradual curve, would have been required. Space
was limited so this technique was out of the question.
By using a camera in a fixed position with a telephoto
lens, I was able to record extreme closeups. Parallax was 21
kept to a minimum because the field of view was very small.
Although only a few steps could be recorded out of any
series of movements, it was deemed that a sufficiently
large number of representative steps used in the final
analysis would negate this drawback.
Observation methods; Swimming
All swimming was; done in a custom built plate glass
tank 203.2 cm by 40.6 cm by 121.9 cm as shown in figure 2.
Although the tank was structurally sound using RTV rubber
sealing compound alone, an aluminum framework was con
structed and fitted around the edges of the tank. Addi
tional sealing compound was placed between the framework
and glass, providing additional support to make the tank
portable when full of water. The stand was of an open
frame design so that observations could be made from beneath
the tank.
The tank was built to satisfy the same basic require
ments as the walkway. That is, the animal had to be free
to move within a defined space that would permit the animal
to make natural and unencumbered movements while restrict
ing its path. In addition, the tank had to be deep enough
' so that the duck could not reach the bottom of the tank
with its foot, or it would walk rather than swim.
The water was cleaned frequently during filming ses
sions because the ducks quickly fouled the water, and the
slightest amount of turbidity had marked effects on picture
clarity. 22
The water in the tank was kept static in preference to a moving water system such as that used by Prang and Schmidt-
Nielson (1976). My own work with cats, (Messinger, 1974) and that of Wetzel (1975) and Tucker (1968) indicate that movements made by an animal on a treadmill, or by an animal trying to maintain its position in a moving water system must be very different from those of an animal trying to propel itself through water that is not moving.
Contrary to popular belief, a swimming animal or human does not try to move its limbs through the water for pro pulsion. The act is better thought of as being an attempt by the swimmer to stabilize a distal and movable part of its body in the water and then draw its body forward using that stabilized part of its body as a fixed point. Any movement of the "paddle" area through the water is called
"slippage". It is essential to keep slippage to a minimum since it results in wasted effort. Slippage may be toler ated, however, if it places the limb in a position that gives it some form of postural advantage, perhaps by allow ing a larger muscle group to come into play, or increasing the limb's mechanical advantage (see Cousilman, 1968).
A moving current would upset the balance of forces normally established by the swimmer in relation to the water. Indeed, the entire milieu of eddys and currents normally encountered (see Hildebrand, 1974 for a review) would be upset. For these reasons, in addition to the cost 23 and complexity of a moving water system, the simple and more natural static water system was employed.
Analytical methods
For analysis, the video tapes were played back at slow speed, stopped, and the desired representative sections were photographed frame by frame using Kodak Plus X panchro matic film. Contact prints were then made from these nega tives. The measurements presented were made from these prints and converted to stick figures 4 and 5 (see pages 56 and 58). Attempts to trace the images directly from the television screen were abandoned. The screen of a televi sion is curved, introducing measurement errors since tracing what appeared as a straight line required following an arc over the screen. The image on the screen also tended to lack definition and contrast. It was also deemed desireable to show actual photographs since they lent themselves to the use of a new stereoscopic technique discovered during the course of this investigation and described below.
Stereoscopic viewing
Comparisons can be made between successive frames of the contact prints using the principle of stereoscopy. The principle of the stereoscope is a very old one. According
to Asher (1961), Leonardo da Vinci came very close to in venting the stereoscope. He ably described the concept of both eyes seeing different views of the same scene. It remained for Sir Charles Wheatstone to invent the 24 stereoscope in 1832, he used a mirror device that was very effective, but not without certain drawbacks. For example, a special room had to be constructed to make them. Photo graphy came into being within a short time of Wheatstone's invention, and he had early stereoscopic photographs made.
Later inventors, among them Oliver Wendell Holmes, refined the stereoscope to its present form. Two photographs or drawings of the same scene, each taken from a different location in time or space, are placed at the focal points of two convex lenses. In this way, the rays of light coming from any one point in either picture emerge from the lenses parallel to each other. This gives the effect of placing the subject at a point at an infinite distance from the observer. Less stress is placed upon the viewer's eyes since accommodation for the distance of the subject is no longer a factor.
A steroscope camera is really two cameras in one. The two cameras take their respective pictures of a scene simul taneously. Due to the spacial separation of the two lenses, each photograph is taken from a slightly different position.
Aerial photographs on the other hand, employ a single camera with a single lens. Exposures of the landscape below are taken sequentially in time as the airplane flies a straight course over the terrain. Each photograph records the terrain from a slightly different position. 25
While examining the accompanying contact prints (see
Plates I-VII) it occurred to me that these exposures were not unlike those made by an airplane taking sequential ex posures of the countryside. Each frame in a series of steps presented on the accompanying sheets is taken from the video tapes used for the original collection of data.
Frames of the television occur at a rate of 30 fps or once every 33.33 ms. If the camera is still, and the subject moves, then the view of the subject is one taken 33.33 ms later and consequently from a slightly (assuming the sub ject moves at a relatively slow speed) different angle.
One can then treat any two successive frames as comprising a stereoscopic pair.
The advantages of viewing the data stereoscopically are more a qualitative rather than quantitative asset.
Conventional photography and stick diagrams like those used by previous authors are useful tools only if we acknowledge some of their inherent disadvantages. Locomotion, and the movements of the anatomical structures used by any animal to accomplish it, occurs in three dimensions. While a body or limb moves foreward, it may simultaneously be moving in other directions. We can talk about pitch, roll, or torques, but our understanding of the phenomenon will de pend on our ability to integrate all the movements that are occurring in the real three dimensional world. A three dimensional appreciation is highly desireable from an 26 intuitive even more than an objective viewpoint. It takes a determined and highly sophisticated reader to assimilate the separate descriptions of a limb moving anteriorly and posteriorly, the descriptions of its movements medially and laterally, and the simultaneous movements of the limb up and down. Even then the reader's conception may be con fused. The stereoscopic method, via the illusion of depth allows one to gain a more natural understanding for what is happening. The illusion on motion is also heightened using this technique.
One can develop the ability to view stereoscopic pictures without the aid of any kind of viewer. For in stance, by converging the images of the letters 0 and X, an
X can be made to appear inside the 0, if the two letters are spaced properly on a page. Construct a small card printed with these letters spaced approximately three cm apart, and then produce a fused image with the card near the contact sheets by simply shifting your gaze to the photographs, and the desired illusion will be produced.
During the course of the text, I will constantly be referring to actual photographs of ducks performing the
'movements being discussed. These pictures constitute the data base, for this study and can be found in the appendix
(Plates I-VII).
Since there are 160 individual photographs presented, a system for locating individual frames was developed. 27
Each frame is located and referred to by using three
numbers. The first number indicates which photographic
sheet (one of seven located in the appendix) that contains
the frame. The second number refers to the horizontal
strip, counting from top to bottom, on which the frame is
on. The third number refers to the number of the frame on
its strip, counting from left to right. For example, 543
means the fifth contact sheet, the fourth strip of film
from the top of the page and the third frame from the left
hand margin of the sheet.
An entire series of frames may also be referenced. In
this case, four numbers will be used. The first two refer
to the same information as explained above, however the
last two numbers will be hyphenated. These two numbers
refer to the first and last frame numbers of the series.
Therefore 543-5 is a series of three frames on the fifth
sheet, fourth strip from-the top, frames three through five.
Stick figures
The stick figures presented in the results section of
this paper were constructed as follows. Joint angles v?ere
constructed from the contact prints using basic geometric
<■ construction techniques. Because the images were so small,
tracings were impractical. Instead, an "average" limb was
synthesized. Raikow (1970) presents ratios for the rela
tive lengths of the limb's skeletal components. Because he
presents data from a large number of samples, I used his 28
ratios for calculating the lengths of an ideal limb. I
measured the tibiotarsus of three of my own ducks and used
the average length of this bone as a base from which to use
Raikow's ratios.
The phalangeal-tarsometatarsal joint (foot), the
tarsometatarsal-tibiotarsal joint (ankle) and tibiotarsal-
femoral joint (knee) (see figure 3 for a diagram) could be
seen on the photographs since the feathers of the left limb
were shaved off. White "Krylon" spray enamel paint, a non
toxic product, was sprayed on the subject’s limb to improve
the contrast of the images. These preparations did not
change the duck's behavior to any noticeable degree.
The hip joint could not be seen distinctly, so the
acetabulum was located by extrapolation. It could be seen
that the acetabulum did not oscillate in the vertical plane,
so the joint was located using the method described by
Rylander and Bolen (1974). In brief, their method utilizes
successive frames. The length of the femur is used as the
radii of two circles drawn around the knee in each frame.
The acetabulum lies where the two circles intersect. This
method was modified for the walking sequences since small
'vertical displacements of the body were apparent. The knee
joint was used as a reference point again. However its
distance from the walkway was measured in successive frames
on the photographs, and then using a proportionate distance,
its position was drawn on the stick diagram. From this
calculated knee position, the hip joint was also located. RESULTS
Walking: Knee, ankle and foot angles
Both walking and swimming at a constant velocity on or
in a homogeneous medium can be considered cyclic events.
We can think of walking as consisting of two main phases, a propulsive phase, and a nonpropulsive phase. The propul
sive phase exists when the animal's limb is on the ground and is supporting the body's weight. This may also be called the stance phase. During the stance phase, the limb
first makes contact with the ground, and the shock of the descending body is absorbed. The limb then supports the body as it passes over the limb, and then supplies muscular energy to propel the animal forward. This cycle repeats itself for each step. The nonpropulsive phase of the step begins as the foot leaves the substrate, and may be called the swing phase. During the swing phase, the limb is brought forward in relation to both the body and the ground
for the next step which will begin at foot contact with the ground. Swimming also contains propulsive and nonpropul
sive phases. The propulsive phase begins as the limb is brought posteriorly in relation to the body, and the nonpro pulsive phase, or recovery phase, begins as the limb is brought forward in relation to the body. 30 In the accompanying stick figures, an arbitrary begin ning to the step cycle was chosen. Each step cycle begins just after the limb has completed its propulsive phase of the cycle (the swim cycle also). This point was chosen because at this time both the walking and swimming limbs look very similar.
Figure 6 illustrates the angles measured from the stick figures. Each graph shows the measurements for more than a complete cycle: the graph being expanded by simply repeating points in succession from the cycle. If we first look at the foot (tarsometatarsal-phalangeal joint) angles,
(stick figure 4, figure 6) we see that the foot's distal end is rising away from the ground. This movement appears to be initiated by the ankle joint flexing. The phalanges remain pointing downwards, and the web is closed. As the foot is brought forward, the phalanges are flexed, tucking the foot underneath the body. Photographs (334-344) show that the foot will be brought parallel to the ground as the foot angle approaches 180°. At this time, the knee and ankle are both extending. The knee extends slower than the ankle until about stick 10 in Figure 4 when the knee reaches 115°. The knee then extends faster than the ankle until the knee reaches a peak angle of 204°. Just after this (approximately 33 ms) the ankle extends to a peak angle of 155°. 31
While the knee is reaching its greatest extension
during the swing phase, the ankle is extending and the foot
is being brought closer to being horizontal. The knee
stops extending while the foot and ankle continue to extend.
The foot and ankle increase their rates of extension until
the limb is fully extended (between stick figures 1 and 2).
The limb is never completely straight (see frames 334, 344,
and 345).
Frames 215, 523-4, 613 and 632 all illustrate the
phalanges striking the ground before the "heel" (hallux).
This observation will be commented upon within the discus
sion. It is also apparent from frames 212-4, 331-2, 336,
523j 531-2 and 543 that the duck's foretoes strike the
ground first, and that the middle, and the longest digit,
is the last part of the foot to leave the ground. This
digit appears to provide a final push during the last part
of the stance.
At the contact with ground, the foot becomes horizon
tal and serves as a fixed point over which the body pivots.
The foot angle remains relatively constant for a time (see
figure 4, stick figures 6 and 7) as does the knee until the
- limb passes through the vertical axis. As the body pivots
over the limb, the foot angle begins to decrease and both
the knee and ankle extend.
Just before lift off, the knee and ankle (figure 4,
stick figures 8 and 9) begin to flex. This begins to raise 32 the foot from the ground. In order to maintain toe contact with the substrate for the push off, (see frames 616, 633,
535, 523, 543, 223) the foot must now extend.
The ankle and knee continue to flex into the beginning of the swing phase. During the swing we see that the foot continues to flex. This tucks it close to the body and presents its dorsal surface forward. The foot flexes until the limb again passes through the vertical plane. Now however, the body serves as the "fixed" reference point for the swinging limb. From its vertical tucked position, the foot is quickly extended past the plane horizontal to the ground, and the ankle, which continues to flex, raises the foot still further from the ground. The knee maintains a relatively fixed position. This indicates that the hip is flexing and drawing the leg forward as a unit. Indeed the photographs 525, 526 ana especially 342-6 show the tarsomet- atarsus being thrust forward along the horizontal plane with very little vertical displacement. The tarsometatarsus and phalanges thrust forward, presenting little anterior surface area.
Frontal view of walking
.To add another dimension to the study of the duck's walk, recordings were taken as the subject approached the camera. From this position, an observer can see that as the foot leaves the ground, the web closes, and the foot swings in an arc toward the midline of the body, to about 14° from the vertical (see 62 1-6 and 63 1-6). These move ments occur during flexion, that is the foot is still being lifted away from the substrate. As extension begins, the foot begins to move laterally, until at contact, its axis lies about 19° off the vertical (see 113, 215). As the body pivots over the leg, the leg approaches within 8° of being vertical (just as the other foot makes contact).
Thus one leg moves in an S shaped path as the body rocks medially and laterally over the supporting leg. It is this rocking motion of the body that gives the duck's gait its characteristic waddle.
Swimming: Knee, ankle and foot angles
Figure 5 shows the basic movements of the limb during swimming from a lateral view. The stick figures again represent simplified drawings constructed from the photo graphs in the appendix.
Figure 7 illustrates the knee, ankle and foot angles during swimming. The cycle is begun during maximum flexion of the ankle joint. Like the walk cycle, the swim cycle has a propulsive phase and a nonpropulsive phase also called the recovery phase.
As the foot is brought forward during recovery, the ankle extends from a minimum value of 27° to a maximum value of 146° (see frames 725-6). This extension continues until the end of the propulsive part of the stroke. During this time the foot is quickly extending, thus bringing the 34 phalanges closer to being in line with the tarsometatarsus ana forming a foot angle of 180°. Since the ankle is still extending, the now straight lower limb begins to exert a force having both a vertical and horizontal component.
This begins the propulsive part of the stroke.
It is the reaction forces exerted on the limb during the early part of the propulsive phase as described above, that are most probably responsible for the foot angle going beyond 180° as in the stick figure number 6. There is no corresponding position to this one during the walk.
The ankle and foot appear to be the points most in volved in the swimming form of locomotion. Knee angles remain relatively constant (figures 7 and 8) during the cycle, the range of motion being only about 25°. This is very slight in contrast with the 125° excursions of the ankle and the 135° excursions of the foot.
As the foot and ankle extend during the propulsive phase, so does the knee. This motion drives the foot down ward, thus extending the limb and providing a larger sur face area to the surrounding water. By tremendously decreasing the ankle and knee angles, the moment arm of the leg is decreased. The torque that needs to be generated by the musculature is consequently reduced. The limb can then be brought back to its forward position with a minimum expenditure of energy while also producing a minimal amount of drag. DISCUSSION
In the early stages of this investigation I formed the hypothesis that walking and swimming are very similar move ments (see Introduction). While making some preliminary observations of a duck swimming, I was struck by the fact that if one did not know which form of locomotion was being observed, one could easily be confused. One brief film sequence,made accidently when something scared one of the animals, dramatically illustrated this fact and led to a series of inquiries. The frightened animal in question swam across the tank in panic. When the video tape was played back at slow speed, the duck appeared to be running through the water rather than swimming.
Unfortunately, an intensive study of high speed locomo tion for the duck was not possible. Nonetheless, a relatively high speed sequence is included with the data (see frames
411-6) and will be discussed later on in this paper.
Comparison of the joint angles during walking and swimming
Figure 8 shows that the knee is subject to greater move ment in walking. Its range of motion is at least 126 degrees, as compared to only 33° of motion during swimming.
When a duck is swimming at a slow speed, the ankle joint lies just at the level of the water's surface. The ankle
35 36 does not move horizontally,in relation, to the body at slow speeds. This observation is another indication that there is a lack of movement by the knee. The swimming gait was observed to change with an increase in the animal's velocity and this phenomenom will be discussed below.
Figure 9 can be used to compare the actions of the ankle joints. The two curves are remarkably similar. The range of motion for the ankle during walking is 125° and 119° for * swimming. Although the walking ankle extends to 161° , 15° more than the ankle during swimming, the ankle during the walk only flexes to a minimum of 36° , whereas the swimming duck's ankle flexes to a minimum of 27°. Therefore one curve is offset vertically from the other curve by a few degrees.
The most obvious difference between the two curves appears during the propulsive phase. When walking, the duck flexes its ankle during the time it passes its body over the foot, but during the corresponding propulsive phase in swimming, the ankle extends to a maximum value and then flexes. This also occurs while the body is passing over the foot. Of course, this can be explained by the fact that the physical demands of the two forms of locomotion differ. For instance, t when the body passes over the foot in walking, its weight contributes vertical forces that must be counteracted. One way to counteract these forces is to use the skeletal com ponents of the body to bear the weight of the body. The limb could be kept straight throughout the stance phase. 37
Dagg (1977) found that the Ostrich exhibits this form
of gait. She provides a graph of its gait, and briefly
comments that there is no mid-stance trough for this large
walking bird. When she talks about the mid-stance trough,
she is referring to a phenomenon she observed during the
early stance. The ankle angle of most birds decreases dur
ing this time. On a graph it reveals itself as a trough.
Such was not the case for the ostrich.
It would seem that this style of gait would cause unde-
sireable vertical displacement of the body. Undesireable
that is, if we assume that these nonpropulsive motions con
sume energy that is not contributing to the animals forward
progress.
To minimize vertical displacements of the body, joints
such as the ankle can be flexed at the appropriate moments
in time. Gravity can be used to flex the joints in prefer
ence to energy consuming muscular contractions. Neither
the duck, gull nor the pigeon ever completely straighten
their limbs during the stance.
Another hypothesis concerning the origin of this mid-
stance trough concerns basic muscle physiology. Flexing j the joint during the stance might serve to stretch the ex
tensor muscles that will soon be called upon to provide
tension. Prestretching these muscles allows them to con
tract with greater force (see Close (1972) for a review). 38
During swimming, the ankle can be seen to extend and
flex in a smoother manner than the corresponding movement
in walking as shown by Figure 9. This is possible because
the body's bouyancy effectively negates the effect of the
animal's weight. The animal's limb is thus relieved of its
weight bearing responsibility, so the body's center of gra
vity moves smoothly along a horizontal path. Therefore no
work in the physical sense is done in accelerating the
body's mass. Relieved of these stresses, the limb need not
give, and the mid-stance trough disappears.
The most marked similarity between aquatic and terres
trial locomotion occurs when one compares the curves obtain
ed for the foot angle values (see figure 10). The curve
begins just prior to foot placement for walking, and just
prior to the propulsive phase for swimming. Both curves
show that at this time the phalanges are extended. As
weight is being placed on the foot, during walking, and
water resistance is being met during swimming, both inter-
tarsal joints show a tendency to flex. The walking foot
remains planted as the tarsometatarsus pivots over it, and
the swimming foot "gives" slightly due to the stresses
'exerted upon the water by the web.
By hyperextending in this fashion, the web stays per
pendicular to the path of motion of the body for a longer
period of time. This tends to optimize the ability of the
leg to provide a backwards thrust against the water 39
(observe frames 736-8 for a better appreciation of the actual movements being referred to). The shapes of the two foot angle curves are remarkably similar although we can see that the respective foot positions are actually differ ent. The foot remains parallel to the line of motion dur ing the propulsive part of the walking cycle, and perpendi cular to the line of motion during the swimming cycle.
Comparison of the swing phases
When comparing the walking and swimming cycles of the duck, it is the two swing phases that show the most simi larity. Compare the swimming series 721-6 and 731-6 with the walking series 521-6. Notice the exaggerated lifting of the foot during walking. Especially apparent is the closing of the web and the flexion of the digits during protraction. These walking movements are very similar to those that occur during the recovery (swing) phase of the swim cycle.
Why does the web open and close during terrestrial locomotion? Why do the phalanges flex as much as they do?
If we view the duck walking from the front and the rear
(see 111-6), we gain a good vantage for observing the action of the webbed foot, and the motion of the limb side ways. One can see that the leg does not swing medially to a large enough extent to make interference between the swinging leg and the supporting leg a factor necessitating the closing of the web. One might argue that by closing 40 the web, air resistance is decreased for the swinging limb.
This is true, yet the amount of air resistance at these low velocities is probably negligible. It is my thesis that the similarities observed, such as the closing of the web, the extreme flexion of the digits, and the raising of the foot, can be attributed to the fact that the duck has adopted basic locomotor patterns that can be used in the water and on land. These patterns are mainly the result of selection for movements that either reduce drag, or are involved in supporting the duck's weight. Retaining move ments for walking from swimming that tend to reduce drag is developmentally economical since common neural pathways can be used for both patterns of movement. Drag reducing movements, such as closing of the web, and a high step offer no disadvantages to the walking animal, while water resistance is an important factor to the swimming animal.
Water resistance is responsible for the observation that the recovering foot during swimming forms a more acute angle with the tarsometatarsus than the swinging foot during walking. This is due to the frontal drag the foot encounters. This is probably a passive movement since the
forces are supplied by the resistance of the water rather than by intrinsic muscles.
Comparing the gaits of aquatic and terrestrial birds of different species reveals findings that are predictable
in light of the thesis stated above. That is, walking 41
movements of swimming birds have been modified to such an
extent that they now show similarities in walking gaits not
inherent to more cursorial species.
For example, in Figure 6 we see that the mallard, an
awkward walker, shows the most flexion of the ankle during
the swing phase. Dagg supplies the four reference angles
for eight other birds in her Table II (pg. 533). The non-
aquatic pea fowl has a maximum flexion of only 75°, while
the magpie goose, a presumably more aquatic species, shows
the greatest flexion during the swing phase of any of the
other birds on the table. These findings suggest that
adaptation to swimming does influence the gait of these
animals. It can be seen that the swimming birds reduce
drag during the recovery by flexing the ankle joint. This
brings the limb closer to the body thus reducing the length
of the lever arm, and the frontal surface area presented to
the water. Since drag is a key factor in aquatic locomo
tion, swimming ducks (and other birds) have modified their
movements to mitigate its effects.
At this point it seems appropriate to comment on some observations made and recorded concerning the change in
gaits that occurs as the velocity of the swimming duck in
creases. These data are being discussed at this time be
cause the conclusions drawn, and the principles involved
concern both swimming and walking. 42
Frames 753-6 show a duck moving at a relatively fast rate of speed. The added extension of the limb is obvious, and is also predictable from Prang's (1970) work.
While studying the metabolic cost of swimming in ducks,
Prang noticed that:
The duck, however, was observed to paddle at a constant stroke rate at all swimming speeds. Since the web of the duck's foot appeared to be fully opened at all speeds, increases in swimming speed were probably accomplished by an increase in the length of the path followed by the foot.
Hildebrand (1974) states that the speed of an animal is determined by its stride length and its stride rate for terrestrial animals. Arshavsky (1975) and Goslow (1973) showed that for the dog and the cat respectively, (see
Grillner (1972) for a review) the swing phase remains al most constant at all speeds.
Therefore the duck would be expected to increase the extension of the leg at higher speeds. Since the foot and ankle are fully extended even at slow speeds, the added extension of the little used knee joint and hip joints is expected in both walking and swimming.
In summary, we can say that walking and swimming are basically very similar movements for the mallard duck. The differences that we can observe are specific adaptations of a basic pattern of movements to specific locomotor require ments. These adaptations, such as increasing the role of the knee joint, decreasing the amount of extension of the 43 foot during walking, and increasing the amount of flexion of the foot during the recovery phase during swimming, are adjustments necessary to counteract the effects of weight and water resistance.
Comparison of the intertarsal (ankle) angles of the walking duck, pigeon and gulT
Locomotor data for the walking Silver Gull (Dagg 1977) and the pigeon (Cracraft 1971) are available from the literature.
In her study of the Silver Gull, Dagg presents the ankle angles of the gull at five intervals during one step.
She plots these angles against the corresponding motion picture frames on which they appear. I have regraphed these data after converting the frame references into time in milliseconds by using the formula Time (in ms) equals the number of frames times 1000 ms divided by 24 fps. This shows that the cycle took 296.29 ms. Figure 11 includes the plotted data for the gull as well as Cracraft*s moder ate gait data for the pigeon. Again, the frame references have been converted into real time in milliseconds.
Cracraft's pigeon, moving at a moderate gait, took 384 ms to complete its cycle. My data for the mallard ankle are also plotted on Figure 11. The duck's walk cycle is about
366 ms in duration. All the cycles were shifted along the abscissa so as to be roughly in phase with one another. In this way the leg positions of the birds closely coincide 44 with each other.
All of the ankle angle data available were plotted on the same graph. Unfortunately Dagg used only five widely spaced data points from the entire cycle. The leg posi tions corresponding to Dagg’s graph’s data points in her own Figure #2 are not very clear. It was assumed that
Dagg's minimum point corresponds to the ankle position dur ing the swing phase as shown by the left leg of gull number five in her Figure #1. This position is easily distin- quished in the duck and pigeon data and is used as a common point of reference for all three curves.
Similarities are obvious. Even with the differences in stride time, the slopes and variations of. all three curves are remarkably alike. Each shows two maximum and two minimum values. Dagg discusses two maximum and two minimum points for the ankle angles of the walking gull.
None of the three birds exhibited a straight limb
(ankle angle of 180°) during their respective step cycles
(upward deflections of the curve represent extensions of the ankle and downward deflections represent flexion). All three birds show maximum ankle flexion during the swing phase. This helps raise the foot off the ground. All three birds show another minimum point during the early stance phase. These results may have been predicted on the basis of Grillner's work in 1972. He states that during the early stance, (he calls it the yield) maximum stress is 45 placed upon the limb. At this time, the extensor muscles giving support, may even be stretching (while actively supplying tension) because the joints are in fact closing under the large forces encountered. Fortunately these stresses were later measured by Clarke and Alexander (1975) in their study of the forces encountered by running quail.
They found that when they graphed the force exerted the ground against time, a graph with two force maximums was obtained. The first and largest maximum occurs as the foot touches the ground for the stance (which verifies Grillner's yield hypotheses) phase. This is logical since in addition to the body’s weight, the kinetic energy of the body would be transferred to the ground through the suddenly deceler ated limb. Later on during the stance phase, as the limb extends to accelerate the body forward, another force in crease occurs due to the body's weight and the forces gen erated by the bird's leg muscles. There seems little reason to doubt that Clarke's force graph should not fit most any alternating-gait biped. It lends a great deal of validity to the observed similarities in all four birds.
Differences obviously do occur between the gaits of
"these species. For instance, the duck's ankle extends as far as 161° and flexes to an angle as close as 36°, a range of 125°. The gull extends its ankle as far as 185° and only flexes it to about 72° during a gait of moderate speed
(a range of 103°). Cracraft's pigeon, at a moderate gait 46 exhibited a maximum ankle extension of only 146° and a flexion of 65° giving it an excursion of only 101° through one stride.
Frames 215, 523-4, 613 and 632 all illustrate the phalanges of the duck striking the ground before the heel.
This does not appear to be a method common to all the birds examined in this study. Cracraft (1971) tells us that for the pigeon, the hallux and foretoes touch the ground "at very nearly the same time" and that the toes are extended as the leg prepares to touch the ground again. This is unlike Dagg’s gull in which the heel strikes the ground before the toes (see her Figure #1, sketch 3). The quail also makes contact with the heel before the toes according to Clarke and Alexander (1975). Why there should be such variation during this part of the step between species is uncertain. We may speculate that it has something to do with the type of terrain each species encounters most often, or perhaps with an important function of the foot during some other activity that might influence the step much as swimming influences the walk cycle. CONCLUSIONS
1. Walking movements and swimming movements of the duck are
very similar, especially at high speeds.
2. The mallard' s knee and ankle move synchronously during
walking and swimming.
3. The knee joint plays a large role in walking, and a rela
tively minor role in swimming, at slow speeds. During
swimming, bouyancy frees the knee joint from its weight
supporting role.
4. The knee joint is involved to an increasing extent as
swimming speeds increase.
5. Birds that use muscular tension to maintain limb stability
during the stance phase (for example, ducks, pigeons and
gulls) do not completely straighten their limbs during
walking. Analysis of their ankle angles will show a
slight angular decrease during the stance.
6 . Birds that use skeletal elements to maintain limb stabil
ity during the stance phase (for example the ostrich)
will completely straighten their limbs during walking.
No decrease will be seen in the ankle angle during the
early stance.
47 The movements of the ankle joints of the duck, pigeon, and seagull show similarities during walking that indi cate the existance of neuromuscular patterns common to all walking birds.
Swimming birds use the basic movement patterns of walking birds. Swimming birds show differences in their gaits resulting from modifications pertaining to the effects of drag and gravity.
Birds that swim will show modifications in their walking gaits. These modifications, such as an exaggerated lift ing and tucking of the foot, show the influence that swimming adaptations have made on the basic bird gait pattern. FURTHER INVESTIGATIONS
The findings of this investigation suggest that more work needs to be done. I would like to see subjects studied with cine radiography and flouroscopy. Using X-rays would elimi nate most of the errors that arise when trying to ascertain the exact location of the skeletal elements in the limbs.
There also exist at this time television cameras that are interfaced with computers. The computers are programmed to use the electronic signals produced by the television camera to analyze quantitative measurements made while the subject locomotes. Velocities, accelerations, forces, angles, and torques can all be measured, and graphed automatically by having the subject, appropriately prepared, pass in front of the cameras.
Electromyographic studies would prove of interest in determining the activity sequences used by the muscles involved in locomotion. These findings would also shed light on the evolutionary development of locomotor patterns.
It would be interesting to perform rigorous tests to determine if and how a moving water system would change the swimming gait of a swimming bird as compared to a static water system. Perhaps a non-swimming bird could also be tested in such tanks. The observations might prove informative. 49 BIBLIOGRAPHY
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50 51
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Tucker, V.A. 1968 Respiratory exchange and evaporative water loss in the flying budgerigar. J. Exp. Biol. 48:67-87. 52
Wetzel, M.C., A.E. Atwater, J.V. Wait, and D.G. Stuart. 1975 Neural implications of different profiles between tread mill and overground locomotion timings in cats. J. Neurophysiol. 38:#3.
Wilcox, H.H., 1952 The pelvic musculature of the loon, Gavia immer. Amer. Midland Nat., 48:513-573. Walkway for Observing Ducks Walkin Tank for Observing Ducks Swimming Ankle Angle
Foot Angle
Fig. 3 Diagram of Ducks's Leg with Joint References 204°
5 4 . 3 2
Fig. 4 Stick Diagrams of the Walking Duck Cn cr>
r- Figure 4 (Continued)
70°
73°
115°
235
193'
10 9
Ln '-J 108° 108° 133° 125° 125°
146
104° 67° 101° 139° 122°,
160, 158' 148° 180°1 140.
Fig. 5 Stick Diagrams of the Swimming Duck F ig u r e 5 (C ontin ued)
117 112 105 100 100
81°
m k27°
66 °
147° 05°
13 12 11 10 9 8
Ln v£> 200
v> .—I0) on c
00
• A nkle
0 Knee
0 Fool-
I 5 1.0 S t i c k F i g u r e 15 20
Fig. 6 Ornph of Knee, Ankle nnd Foot Angles During the Wnlk Cycle
200°
o--
10 0 °
5 0 °
20 0 A nkle Stick Figure Fig. 7 Graph of Knee, Ankle, and Foot Angles During Swimming n Knee 0 F o o t
O' 300'
150°
■D-'
100°
70°
1 5 Stick Figure 10 15
0 Walking Knee Fig. 8 Graph Comparing Knee Angles of the Walking and Swimming Duck • Swimming Knee
A n g le s 250 200 150° 10CP ° 5 10 64 A n g le s 200 ' geon n o e ig P □ 1 Duck Duck 1 * Gul 1. Gul * g. ah rng Ankl Angl of the Wal ng Duk Il n Gull u G and n o e I’lg uck, D g in lk a W e h t f o s le g n A le k n A g arin p m o C raph G I I . ig F T S 166. 3 47 633 467 333 .5 6 6 1 UT,S' m ' O Plate I. Rear and Lateral Views of Walking
With Lateral Views of Swimming
66 Plate Plate II. Rear View of Walk with Lateral View of Swim
68 Plate II Plate III. Lateral View of the Walk Plate III Plate IV. Moderately Fast Swim Plate IV
V -y.
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/ - —
4 -bJ 9 >-. g t-> -L«*a gg§i llil Iggiiil HHHjLL vBB ^ ^ T T T ? ?♦ WBBKMmI
> ' W ■ ■ p - „ \i ’- - ^ - HHSKr^ ...... ,.T jgfeSiF Jll pp!piSiSfM ^ ^M5»;.^ s ,^tmm ’- / — '^A*' ■•„ '£T* ? Ji ”? Plate V. Closeups and Multiple
Exposures of the Walking Duck
74 Plate V Plate VI. Frontal and Lateral Views of the Walk Plate VI Plate VII. Fast and Slow Swimming
78 Plate VII