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Effect of solar eclipse on the behavior of a captive group of chimpanzees (Pan troglodytes).

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American Journal of Primatology 11:367-373 (1986)
Effect of Solar Eclipse on the Behavior of a Captive Group
of Chimpanzees (Pan troglodytes)
JANE E. BRANCH' AND DEBORAH A. GUST1r2
'Yerkes Regional Primate Research Center, Emory University, and 'School of Psychology,
Georgia Institute of Technology, Atlanta
A captive group of chimpanzees, housed in a n outdoor compound at the
Yerkes Regional Primate Research Center, was observed during the annular
solar eclipse of May 30, 1984. The behavior of each animal was recorded
using a n instantaneous scan-sampling technique (Altmann: Behaviour
49:227-265, 1974). Beginning 2 days prior to the eclipse and continuing
through the day following the eclipse, data were collected from 1100 to 1300
hours daily. At 1214 hours on the day of the eclipse, when the sky began to
darken and the temperature began to decrease, solitary females and females
with infants moved to the top of a climbing structure. As the eclipse progressed, additional chimpanzees began to congregate on the climbing structure and to orient their bodies in the direction of the sun and moon. At 1223
hours, during the period of maximum eclipse, the animals continued to
orient their bodies toward the sun and moon and to turn their faces upward.
One juvenile stood upright and gestured in the direction of the sun and
moon. Sunlight began to increase a t 1225 hours, and as it became brighter,
the animals began to descend from the climbing structure. The behaviors
exhibited by the group during the period of maximum eclipse were not
observed prior to or following the eclipse nor as darkness approached a t
normal, daily sunset. These data indicate that a solar eclipse, a rare and
uncommon environmental event, can influence and modulate the behavior
of chimpanzees.
Key words: apes, sun, environmental phenomenon
INTRODUCTION
On May 30, 1984, the Atlanta area experienced a n annular solar eclipse. Approximately 99.7%of the sun was blocked out by the moon, leaving a ring of light
around its periphery. The path of the eclipse extended from Louisiana to Virginia.
The event began at 1150 hours, and by 1223 hours the eclipse had reached annularity, its nearest approach to totality (maximum eclipse). At annularity, the moon
appeared as a black spot between the earth and sun, surrounded by a ring of light.
The previous solar eclipse observable in Atlanta occurred on May 28, 1900, and the
next total eclipse visible from Atlanta is predicted to occur on May 11, 2078.
Received March 12,1986; revision accepted June 22, 1986.
Address reprint requests to Deborah A. Gust, Yerkes Regional Primate Research Center, Emory University, Atlanta, GA 30322.
0 1986 Alan R. Liss, Inc.
Solitary
Sitting
Sitting, eating,
drinking
Self-grooming
Playing alone
Lying, eating,
drinking
Standing
Standing,
eating,
drinking
Looking
Rocking
Other
Interactive
Approaching
Touching
Reacting to
Taking object
from
Grooming
Sitting near
Playing
Chasing
Mother-infant
Other
Displace
Hit
Other
Aggressive
Other directed
Nondirected
Vocalizations
Climbing
Walking
Running
Rolling
Locomotion
Sitting
Lying
Standing
Walking
Running
Other
Postural
TABLE I. Behavior Categories Used for Instantaneous Scan Samples of Chimpanzees
Pulling object
Pushing object
Examining object
Other
Manipulative
Mounting
Inspecting
genitals
Courting
Touching
Sexual
-
o u t of
view
Solar Eclipse and Chimpanzee Behavior I 369
Studies of animal behavior during a solar eclipse have been relatively sparse.
Within the last few years, reports have described the phenomenon in, for example,
waterfowl [Loftin, 19711, freshwater fish [Pandey & Shukla, 19821, songbirds [Elliot
& Elliot, 19741, egrets [Kumar, 19811, and rodents [Advani, 19811, but few have
described the reactions of nonhuman primates to a solar eclipse. Dixit et a1 [1981]
and Mukherjee [1984] studied rhesus monkeys, and Mohnot [1981] studied Hanuman langurs during the 1980 solar eclipse in India. Mukherjee [1984] reported
noticeable behavioral differences in rhesus monkeys, and Mohnot [ 19811 noted few
behavioral changes in langurs during the eclipse.
The present report describes changes in the behavior of a group of chimpanzees
during a solar eclipse in Georgia. The study capitalized on the location of a research
site, which was within the path of the annular solar eclipse, thereby providing the
opportunity for a n unusual experiment involving the behavior of the chimpanzees.
The objective was to observe, record, and characterize the behavior of a group of
common chimpanzees housed in a n outdoor compound before, during, and after the
eclipse to determine whether the animals would exhibit discernible changes in
behavior during the period of the eclipse.
METHODS
Sixteen common chimpanzees (Pun trogladytes) of both sexes served as subjects
for the present study. Subjects were identified as infants (n = 41, juveniles (n = 31,
adult females (n = 8), and adult male (n = 1).All were contained as a social group
within a 23.77 x 29.26-m outdoor compound a t the Field Station of the Yerkes
Regional Primate Research Center. The perimeter of the compound comprised openmesh fencing 2.1 m high and 4.77 m of sheet metal above the fencing. The compound
was not covered, and its location provided a direct, unobscured view of the sun and
moon during the eclipse.
During 2-hour periods on 4 consecutive days, the subjects were observed from
an elevated platform overlooking the compound, and the behavior of each animal
was recorded on a behavioral checksheet during successive 10-minute scan-sampling
periods (Table I). Weather conditions were characterized and recorded for each scan
sample.
Data were collected from 1100 to 1300 hours daily beginning 2 days before the
eclipse and ending 1 day after the eclipse, yielding a total of 45 scan samples in
addition to 3 sample periods during the actual eclipse when only a videotape record
was obtained. Prior to data analysis, interobserver reliability was assessed using
the checksheets, and i t was found that the two observers were in agreement on 91%
of the scans. On the day of the eclipse, the vocalizations and behavior of the group
were also recorded and videotaped during the sampling periods. Unfortunately,
behaviors that changed a t the onset of and throughout the eclipse (e.g., orientation,
position on the climbing structure, gestures) were not included on the checksheets;
thus, statistical analyses were not possible. In addition to the 4-day observation
period, the animals were observed during normal sunset to determine whether
behavior patterns exhibited a t the end of the day were similar to those noted during
the eclipse. Using behavioral checksheets, six scan samples were obtained during a
1-hour period preceding sunset.
RESULTS
Subjects were observed on the climbing structure on 2 days preceding and 1day
following the eclipse. In contrast to behaviors exhibited during the eclipse, the
chimpanzees that were on the climbing structure, on the days preceding and following the eclipse, oriented toward other animals and objects within the compound a t
or below eye level rather than toward the sky. No more than four individuals were
Fig. 1. Sequential frames of videotape showing the behavioral activities of a group of chimpanzees prior
to, during, and following an annular solar eclipse, Changes in level of ambient illumination associated
with the eclipse precluded clearer video-recordings of the subjects. Descriptions of successive frames are
included in the text.
Solar Eclipse and Chimpanzee Behavior / 371
observed on the climbing structure a t any one time, and no animal remained on the
structure for more than 20 minutes.
At 1214 hours on the day of the eclipse, as the sky began to darken and the
temperature began to decrease, individuals in the group exhibited atypical behaviors. Solitary females and females with infants moved to the climbing structure and
ascended to the topmost positions (Fig. 1A). At 1216 hours, other animals moved to
the climbing structure, ascended, and congregated near the top, sitting and standing
in close proximity to one another and orienting their bodies toward the sun and
moon. At 1217 hours, individuals continued to move to the climbing structure and
to face toward the direction of the sun and moon. At 1220 hours, all animals on the
structure were orienting toward the direction of the darkened sun. At 1222 hours,
one chimpanzee momentarily stood upright on top of the climbing structure (Fig.
lB, arrow). In addition, some animals turned toward the direction of birds heard
singing outside the compound, then resumed their sun-orienting postures (Fig. 1C).
At 1223 hours, the onset of totality, all animals on the structure oriented toward the
sun and moon with their faces turned upward, and one animal gestured as if
pointing in the direction of the sun and moon (Fig. 1D). During this time, the adult
male and three adult females rested quietly along the shaded periphery of the
compound.
Sunlight began to increase a t 1225 hours, but the animals on the climbing
structure continued to orient toward the sun and moon (Fig. 1E). Shortly, thereafter,
two animals climbed to a lower portion of the structure, and some began to shift
their gaze away from the sun and moon (Fig. 1F).Two animals, previously limited
to lower positions on the structure, ascended to the top once those positions were
vacated and then oriented toward the sun and moon (Fig. 1G); 2 minutes later, they
descended from the highest point. At 1235 hours, as brightness increased, more
animals descended from the climbing structure, and two females at the top of the
structure continued to focus in the direction of the sun and moon (Fig. 1H). One
adult female and a juvenile male, previously resting along the periphery of the
compound, moved toward the center of the compound. Figure 1 H (arrow) shows an
adult female holding a n infant while a second animal places her hand on the
female’s shoulder. Throughout the eclipse, all animals remained in the open compound, and none entered the indoor living areas. It was 1245 hours before the group
descended from the structure and exhibited behaviors typical of those observed prior
to the eclipse (Fig. 11).
When the group was studied, subsequently, during normal sunset to compare
the effect of diminishing light a t sunset and at the onset of the eclipse, the animals
did not group together on the climbing structure as darkness approached. At 1710
hours (50 minutes prior to sunset), half the animals were walking around the
compound, and half were sitting alone at various positions. At 1720 hours, two
juveniles were sitting on the climbing structure and seven females were on the
ground, three in close proximity to each other and four sitting alone. The remaining
animals were in the indoor living area and out of view. By 1750 hours, all animals
were in the indoor areas, and at 1800 hours (sunset), two animals were seen sitting
near the entrance to the indoor areas.
DISCUSSION
Several investigators [e.g., Goodall, 1968; Kano, 1971; Nishida, 1970; Sugiyama,
19681 have provided considerable data on typical chimpanzee behavior and ecology,
but there are few reports on the behavioral reactions of chimpanzees to infrequent
or aperiodic natural events. Goodall [1968, 19711 and Bygott [1979] noted an apparent behavioral reaction by chimpanzees to weather conditions. They reported that
372 I Branch and Gust
the animals exhibited a type of “rain-dance” during very heavy rainfall. The behavior was typically initiated by one adult male and included irregular “pant hoot”
vocalizations accompanied by charging while breaking and dragging branches, The
“rain-dance” ceased when the rainfall began to subside.
As in the case of the “rain-dance” phenomenon, most of the behaviors exhibited
during the period of annularity in the present study were not seen prior to or
following the eclipse, nor during normal sunset. The most salient behavior noted
during the eclipse was grouping in close proximity a t a n elevated level above the
compound floor and orienting toward the sun and moon. Mukherjee [ 19841 reported
that a group of rhesus monkeys, which traveled and behaved as a unit under normal
conditions, divided into subgroups and bedded down during maximum darkness of
a n eclipse. Similar to the subjects of the present study, the monkeys resumed typical
behavior patterns a t the end of the eclipse. The chimpanzees’ atypical behavior
during the annular eclipse in the present study did not correspond to previous
reports of nonhuman primates during a solar eclipse [eg, Dixit et al, 1981; Mukherjee, 19841; however, direct comparisons are difficult given the different living environments, weather conditions, and degrees of eclipse.
The present study documents the effects of a salient environmental event on the
normal, daily activity patterns of a social group of chimpanzees living in a seminatural environment. Behavioral changes have been reported for several other species,
but there have been no previous reports of the phenomenon in chimpanzees. Wojtusiak and Majlert 119761 reported that the behavior of several species can be affected
by a solar eclipse; thus, it should not be surprising that a n eclipse can produce
marked changes in the behavioral activity patterns of chimpanzees in a seminatural
environment. The behaviors observed in the present study were undoubtedly not
characteristic of the group under normal conditions nor during sunset on normal
days. Unfortunately, the low frequency of occurrence of a total solar eclipse in any
given area makes subsequent studies with a group of subjects very difficult. The
present study can serve as a stimulus, however, for planning additional studies in
conjunction with the next predicted solar eclipse.
CONCLUSIONS
1. During the annular solar eclipse of May 30, 1984, a group of chimpanzees
housed in a large outdoor compound exhibited behaviors that were not observed
during scan samples taken before and after the eclipse.
2. The chimpanzees gathered in close proximity on a climbing structure situated
in the middle of the compound and oriented their bodies toward the direction of the
sun and moon during the eclipse.
3. Similar behaviors were not observed during a typical, daily sunset.
ACKNOWLEDGMENTS
The authors thank Dr. L.D. Byrd and Ms. P.M. Plant for comments during the
preparation of the manuscript and Dr. T.L. Maple and Dr. R.B. Swenson for help in
arranging to conduct the study. This research was supported, in part, by U.S. Public
Health Service grants DA-01161 and RR-00165 (Division of Research Resources,
NIH) to the Yerkes Regional Primate Research Center. The Yerkes Center is fully
accredited by the American Association for Accreditation of Laboratory Animal
Care.
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Solar Eclipse and Chimpanzee Behavior I 373
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