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Differences in terrestrial velocity in Macaca and Presbytis.

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Differences in Terrestrial Velocity in Macaca and
Presbytis
THEODORE I. GRAND
Oregon Regional Przmnte Rc7senrrh Center, 505 N.W. 1 8 5 th Avenue,
Ben-oerton, Oregon 97005
KEY WORDS
Pres bytis.
Locomotor behavior . Ground speed . Macaca .
ABSTRACT
Over 150 sequences of terrestrial movement were timed and measured i n the toque macaque, the gray langur, and the purple-faced langur to determine the relation between velocity, gait, and psychosocial context. Species differences were found in mean velocity, “favored” gait, and surface preference. All
three species used the walk and the gallop at the slowest and fastest speeds respectively. The macaques and gray langurs walked frequcntly, but the purple-faced
langurs were never seen to do so. At intermediate speeds, the macaques used
either the “fast” walk or the “slow” gallop, whereas the gray langurs used irregular patterns of walk-gallop-walk-gallop. The purple-faced langurs were faster
(about 20 fps) and less variable than the other species, regardless of distance.
These data suggest that motor expression varies among the Cercopithecoid monkeys; the correlation between locomotion and anatomy is not as close as it is
among wholly terrestrial or arboreal forms; slowness i n the macaque is an expression of social confidence, not of biomechanical inability, high speed i n the purple-faced langur is due to psychosocial factors rather than to “terrestrial” adaptability.
The subject of this paper is the use of one can establish the relation between supground speed to measure the behavior of port surface and body structure. An adethree monkeys, a macaque and two langurs. quate functional-anatomical paradigm reThis analysis is part of a broader exam- sults.
Most primates, however, divide their time
ination of the ecology and sociology of Ceylonese primates (Eisenberg et al., ’72; Rip- between canopy supports and the ground,
and the clear-cut distinction seen i n the
ley, ’67, ’70; Dittus, ’74).
One focus of the overall study, habitat above animals is less sharp (Rose, ’73).
preference, is a debated issue of primate Those South American forms which spend
behavior. The confusion is partly due to the 100% of each day i n the trees cannot be
clear terrestrial-arboreal dichotomy of other judged structurally “incapable” of moving
lineages. Completely arboreal and terres- on the ground.
The African and Asian species move
trial forms have appeared over long time
periods and represent extremes of some about i n a more flexible and diverse fashion.
theoretical ground-canopy continuum. In Thus, they are somewhere within the centhe horse, for example, surface occupation ter of the ground-canopy continuum. That a
and extreme anatomical adaptation are moderate degree of surface occupation imclearly correlated. The three-toed sloths, by plies structural adaptation must be proved
contrast, spend almost all their time within in each case. What may look like a n adapthe canopy, descending awakwardly for tation to one surface may be the preferonly a few minutes once a week. This polarization of habitat is unequivocal, and the
1 Publication No. 823 of the Oregon Regional Primate
anatomical extensions are unquestioned. Research Center, supported in part by Grants RR-00163
from the National Institutes of Health, USPHS. and by
By simply measuring the time spent by a the Smithsonian Biological Program i n Ceylon (Primatr
given species upon one or the other surface, Ecology Survey)
AM. J. P H Y S A
. N T H R O P . , ~101-108.
~:
101
102
THEODORE I. G R A N D
ence of the local population, not a structural character of the species.
Therefore, in this comparison a simpler
question than what "percent time" is spent
on one surface is posed: While a n individual
is o n the ground, what does he do, how far
does he move, how much time docs it take?
In other words, how fast does he travel? The
toque macaque, gray langur, and purplefaced langur, living within the same habitat, provide a three-way comparison and
narrow the discussion to two fundamental
questions: Does the toque macaque, which
differs structurally more than the other
two species, also differ more in speed? Are
the two structurally similar larigurs also
similar i n the way they travel over open
ground?
The conclusions from these data relate
velocity and gait pattern, on the one hand,
with the social context of individual movement. on the other.
METHODOLOGY
The three species - the toque macaque
(Mncaca sinica), the gray langur (Presbytis en tellus), and the purple-faced larigur
( P , senex)-were
observed in the open
parkland habitat of Polonnaruwa, Ceylon.
Tree crowns overlapped in some places but
were discontinuous in others. This structural fact, as well as the availability (or lack)
of food, brought each of the species to the
ground for some part of each day, although
on occasion P. scnex remained aloft for
several days. Where the shrub layer was
cleared, the short grassy cover made i t
easy to observe and measure the animals.
Over 150 movement sequences were
timed to the nearest 0.1 second and tape
measured to the nearest foot. Each point
in figure 3 is one sequence in feetisecond
(fps), the triangle representing the walk,
the circle the gallop. In each case, the associated gait, age, and sex of the individual,
as well as the psychosocial bases of the
movement, were observed. Each sequence
was judged for linear directness, evenness
(lack of overall acceleration and deceleration), and gait regularity. Irregular sequences like those among the gray langurs
(i.e., walk-gallop-walk-gallop) are described
separately and eliminated from the calculations of mean velocity. Film records from
which tracings were made are included.
Sampling differences occurred which reflect
presumptive behavioral differences. The
gray langurs and macaques were easy to
approach and measure, but the macaques
ran at higher speeds only in complicated
chase sequences. The purple-faced larigurs
were difficult to approach and I never saw
them walking over open ground; they did,
however, walk frequently within the canopy.
Because of the stereotyped and isolated
movements of these langurs, I was able to
anticipate them. While at some distance removed, I could time accurately each in&vidual and identih take-off and target
points: after the troop had relocated, I could
approach and tape measure the distance.
OBSERVATIONS
i " u c n sinica. The biomechanics of the
two gaits should he characterized. The walk
is used at the slowest speeds (fig. 1A). At
least one hand or foot is in contact with
the ground at any instant. Most commonly,
the limbs move in diagonal pairs, that is,
one hindlimb and the diagonally opposite
forelimb. Occasionally, the hindlimb and
forelimb on the same side are moved together, a lateral sequence gait. The body mass
has low vertical dlsplacement and little acceleration. A complete cycle takes about
one second.
The run or gallop is used for higher
speeds (fig. 1B). The forelimbs and hindlimbs move in pairs, and right and left
palms (and soles) strike closely in time. In
the earlier phase, the second foot contact is
almost completed, the palmas contact just
begins. In the later phase, the body is off
the ground but for the right palm. Within
each cycle, one or two periods occur when
the body is off the ground. The trajectory
of truncal mass moves through an arc with
greater vertical displacement and greater
change i n acceleration. Two cycles may be
completed within one second. (For detailed
analyses of gait formulas, see Muybridge,
'57; Hildebrand, '67; Prost and Sussman,
'69.)
Along the top of the graph (fig. 3A), the
slowest speeds are associated with the walk;
along the bottom, the faster movements are
correlated with the run or gallop. The walk
averages 3 fps; the run 10 fps. Occasionally
these animals move at very high speeds.
Circular and irregular chase sequences at
15 f p s were difficult to measure.
At intermediate speeds, the gaits were
SPEED I N MACACA AND P R E S B Y T I S
/
\
a
j
i
104
THEODORE I. GRAND
intergraded. Sometimes a “fast” walk or a
“slow” gallop was employed at the same
speed. At these intermediate speeds, the
animal had a choice of gait in moving from
place to place, the choice reflecting the social circumstances and their impact upon
the individual. This relation of speed and
gait to state of mind are elaborated upon
within the DISCUSSION.
Troop movement is a combination of slow
and fast gaits of all members. Walking
and moderate running were frequent and
equally easy to measure. Some individuals
appeared to be leading the troop, others trying to catch up. Chase and pursuit within
the troop’s flow were irregular, occasional
incidents of social life. Together the slowest and fastest sequences averaged 5 fps.
This approximation provides some idea of
the slow rate of macaque travel.
Presbytis entellus. Out of 73 observations, only ten walking sequences could be
measured. The animals had the peculiar
habit of walking a few steps, galloping a
few more, walking a few, and then abruptly
sitting. Eliminating this irregular pattern,
used commonly at intermediate speeds,
caused the striking separation of low-speed
walk froni high-speed gallop.
The gallop varied both in distance covered and in time elapsed (6 to 20 fps) : both
short and long distances were covered slowl y and quickly; the average was 11.5 fps or
7.8 mph.
One structural characteristic of the galloping langur diverges significantly from
that of the macaque. Whereas the latter
moves with a relatively straight back, the
langur flexes (or gathers) its back to about
two-thirds of its length (fig. 2 ) .
Change of lead, designated by the forward striking hand or foot of a pair, was
common during the gallop. In three successive cycles, a n animal might strike with
the hind feet leftlright, leftlright, leftlright,
while the forefeet alternated leftlright,
rightoeft, left/right. Change also occurred
between hindlimb and forelimb strike. Analyses of six long film sequences showed no
regular or favored patterns. Most likely, i f
the animal did not alternate leads, he
Fig. 3 Velocity and gait pattern graphs (Triangle represents walking sequences; circle represents
galloping sequences). A , M. sinicn. B, P. cntcllus.
C, P. senex.
105
SPEED I N M A C A C A AND PRESBYTIS
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102233fps (n.27)
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100
80
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40
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100
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160
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180
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60
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DISTANCE ( feet 1
Figure 3
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220
240
I
260
106
THEODORE I. GRAND
would drift toward the right or left. Why
the gray langurs, but neither the macaques
nor the purple-face langurs, use frequent
lead changes is not clear. The latter ccrtainly do not drift away from their intended
lines of travel.
Older infants and juveniles, 5 to 15
months of age, tended to move at higher
speeds than adults. About 20 sequences
were measured. The young appeared more
wary as they approached the ground, looking about from the base of the tree trunk
before going “all out” to reach the target
tree. Sometimes a young animal lagged behind mother and troop, then ran to catch
up with her. Females moved in a slower,
more irregular fashion. Thus both age and
sex differences in movement are suggested.
Like the macaques, the langur troop
moved in amoeboid fashion, spread out i n
time and space. E. g., one animal covered a
distance and stopped, a few minutes later a
second animal moved in the same direction,
over a roughly parallel route, but not on a n
identical pathway. Over the next half hour,
other animals moved in the same direction.
During this shift, feeding sometimes took
place. When the animals approached the
target trees, individuals chose to climb different trees. In this watchful, but not anxious manner. the entire group moved slowly
forward.
Presbytis senex. These animals were
never timed walkmg on the ground (fig.
3C). All 31 sequences show direct, almost
“flat out” movement. In a personal communication, Manley says. “I suspect in all
your measured sequences you have animals
‘making a dash for it’; i.e., moving at maximum speed.” As the graph shows, the rate
of travel was a regular 18 f p s f 2.1 from
20 up to 200 feet. Since this 12.3 mph appeared to be their maximum performance,
the 2 3 mph estimate by Eriders (’46) is difficult to explain.
To move between trees whose crowns
were not connected, the troop had to choose
circuitous routes or come to the ground.
When the latter happened, the first animal
descended to the base of the tree, looked or
scanned about, then in a continuous motion,
dropped to the ground, galloped directly to
the target tree, and hopped into it. Then
the animal looked around once again, and
in less tense fashion, climbed into the higher branches. Each troop member went
through the same stereotyped performance.
The peculiar tension associated with this
point-to-point movement has no counterpart
among the adult gray langurs or the toque
macaques. Because they traveled on the
ground one-by-one in a straight line, they
were easily trapped by dogs (Ripley, personal communication).
DISCUSSION
Obvious differences in average ground
speed clearly distinguish the three species.
The macaques are the slowest and most
variable. They walk and run both short and
long distances and achieve high speeds in
short, irregular bursts. The gray langurs
have about the same average speed arid
they also vary their mode of travel. By contrast, the purple-faced langur is the fastest
and most invariant. Whether traveling 20
or 200 feet, they never varied their speed.
These facts suggest three problems about
motor variability: (1) the anatomical bases
of speed differences, (2) speed on the
ground as a terrestrial skill, (3) the psychosocial stimuli of movement.
The first aspect is the structural bases of
movement. The difference in average running speed between macaque and purplefaced langur is about 9 fps. The macaques,
however, are capable of short spurts of 1517 f p s , close to the maximum speed of the
purple-faced langur. The extra speed of the
latter can be explained by greater trunk
and limb length and greater truncal flexibility. To relate structure to performance
and to distinguish between species, it is not
necessary to use any more precise osteometrics. Performance differences between
the gray and purple-faced langurs cannot
be explained by body structure. The average speed of both differs by 7 f p s , but the
gray langurs were timed at 18-19 fps. Thus,
they were capable of speeds equal to those
of the purple-faced langurs but seldom had
recourse to them.
The second aspect of species variability is
whether speed represents a significant terrestrial skill for these animals. Flight by
antelope and horse and pursuit by cheetah
are described in mileshour, and the
achievement of high ground speed is a significant feature of terrestrial adaptation.
Because of these specialized cases, mph has
become the essence of speed. Absolute
speed measures also suggest comparisons
SPEED IN MACACA AND PRESBYTIS
between smaller and larger animals: the
squirrel and elephant travel at 17 and 15
mph, respectively (Layne and Benton, ’54;
Howell, ’65). Body lengths per unit time
would be a more appropriate scale here; in
fact, speed in mph is irrelevant in smaller
forms and is inadequate in comparing
smaller and larger ones.
Among these primate species, even feet/
second may not be a n appropriate measure
of movement. The purple-faced langur can
run 18 fps, but this performance explains
neither where nor under what selective
pressures the skill evolved. As a matter of
fact, speed is only one facet of survival;
rapid acceleration and the ricochet, both
used to dodge a pursuer or to change direction or place, are other skills related to
speed.
Neither is speed of direct value for life
within the canopy. On the one hand, distance traveled in feet is not the key because
unobstructed linear routes do not exist; on
the other hand, acceleration and jumping
between branches may be the skill transmuted into high speed on the ground. High
speed could derive from arboreal leaping.
In any case, ground speed cannot be explained apart from the other aspects of the
life of the purple-faced langur. We are left
with the paradox that this animal, capable
of the fastest, most regular performance,
spends the least time on the ground.
Within the psychosocial realm we may
find the third potential explanation for
movement differences. The anomaly of
skilled performance upon the ground and
(literal) avoidance of the ground is much
more clearly demonstrated by measures of
velocity and gait of individuals than by
“percent time spent” upon the surface by
the troop. It is more sensitive to the behavior of the individual and leads directly to
the question: What limits the purple-faced
langur to occasional use of the ground, on
the one hand, and gives shared occupancy
to the gray langurs and macaques, on the
other? The particularities of speed lead us
to the same answer: Macaques may choose
to move at a “fast” walk or a “slow” gallop a t intermediate speeds, depending upon
social circumstances; gray langurs, which
spend a great deal of time on the ground,
move at all speeds; and purple-faced langurs, which walk routinely over canopy supports, do not walk upon the ground. How-
107
ever, in the extreme south of Ceylon, near
Calk, Manley found revealing exceptions
to purple-faced langur behavior at Polonnaruwa. In some southern troops the a d mals spent much of their time on “rocky,
virtually treeless coastal slopes.” These
rocky slopes were not “quick-visit places”
for the animals who spent much of the day
on them, resting and feeding on creepers,
herbs, and woody plants growing between
the crevices. “All the animals seemed perfectly at home on these rocky surfaces and
outcrops, sitting, walking leisurely across
them, leaping u p or down from rock to
rock.” In other words the animals were
completely at ease and did not treat the
rocky terrain as a n unusual part of their
habitat. Despite their predilection for trees,
P. senex appear to adapt easily to the
ground when they have to.
At Polonnaruwa all three species are
capable of higher speeds, but only young
gray langurs and purple-faced langurs do
so with any regularity. Among these langurs, tension, apprehension, and wariness
are characteristic features of each animal.
The striking invariance of speed, the feeling that the individuals are moving “flatout,” supports this. Social confidence, state
of mind, and perhaps occasional, as opposed
to habitual use of the ground are the major
forces upon the individual. Among chimpanzees rate of locomotion may communicate information about preferred objects
(Menzel and Halperin, ’75); no doubt these
other states are as easily transmitted among
the monkeys.
We conclude that the bases of high-speed
i n the purple-faced langur are sociological
and psychological rather than anatomical.
Thus, it is not the osteometric differences
among the species but the social organization and attitudes of the local population
which are the bases of terrestrial occupation.
ACKNOWLEDGMENTS
A version of this paper was presented at
the American Association of Physical Anthropologists meetings, held i n Denver,
April, 1975. I gratefully acknowledge the
cooperation of the Smithsonian personnel,
including Drs. Eisenberg, Ripley, Dittus,
Muckenhirn, and Manley and M. Lockhart.
F. Shininger took film records for me. The
ORPRC staff has been of assistance; M.
108
THEODORE I. GRAND
B a s s offered editorial comments once
more. In addition, A. Zihlman and S. Ripley
read and commented upon the analysis.
LITERATURE CITED
Dittus, W. P. J . 1974 The ecology a n d behavior
o f t h e toque monkey: Mnccicci sinicn. Unpublished
Ph.D. thesis, U. Maryland.
Eisenberg, J. F., N. A. Muckenhirn a n d R. Rudran
1972 The relation between ecology a n d social
structure i n primates. Science, 176: 863-874.
Enders, R. K. 1946 Speed i n the langur. J.
Mammal., 27: 174-1 75.
Ilildebrand, M. 1967 Symmetrical gaits of primates. Am, J. Phys. Anthrop., 26: 119-730.
Howell. A. B. 1965 Speed i n Animals. Hafner,
New York.
Layne, J. N., and A. H. Benton 1954 Some
speeds of small mammals. J. Mammal, 3 5 : 103104.
Menzel, E. W., a n d S. Halperin 1975 Purposive
behavior a s a basis for objective communication
between chimpanzees. Science. 189: 6 5 2 4 5 4 .
Muybridge, E. 1957 Animals i n Motion. Dover,
New York.
Prost, J. H., a n d R. W. Sussman 1969 Monkey
locomotion o n inclined surfaces. Am. J . Phys.
Anthrop.. 31: 53-58.
Ripley, S. 1967 Leaping of langurs: A problem
i n the study of locomotor adaptation. Am. J.
Phys. Anthrop.. 26: 149-170.
1970 Leaves a n d leaf-monkeys. The social organization of foraging i n gray langurs.
I n : Old World Monkeys. Evolution, Systematics.
and Behavior, J. R. Napier a n d P. H. Napier.
eds. Academic Press, New York, pp. 481-509.
Rose, M. 1973 Quadrupedalism i n primates.
Primates, 1 4 : 337-357.
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