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Behavioral responses of free-ranging rhesus monkeys to food shortage.

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Behavioral Responses of Free-ranging Rhesus
Monkeys to Food Shortage
JAMES LOYl
Northwestern University, Department of Anthropology,
Evanston, Illinois 60201
ABSTRACT
During early July 1968, a severe food shortage occurred on Cayo Santiago, a n island colony of free-ranging rhesus monkeys (AMacaca muEatta). The food
shortage produced striking changes i n the behavior of the monkeys. Within the one
social group intensively studied, the total frequencies of grooming, play and fights decreased significantly; the frequency of matings also dropped; body contact, displacements by other groups, and non-displacement movements decreased, but not in statistically significant amounts. Changes in the percentage of total grooming attributable
to related and unrelated monkeys reflected the stability of the rhesus matriline.
Comparisons made between Cay0 Santiago and other primate groups under analogous
situations reveal similar responses to food shortage.
Cay0 Santiago lies just off the southeast
corner of Puerto Rico (fig. 1 ) . %At the time
of the present study i t was inhabited by
over 700 free-ranging rhesus monkeys
(Macaca inzilattn) , whose ancestors were
transported to the island from India in
1938 (Carpenter, ’42). Besides the monkeys, the island supports several species of
crabs and lizards, black rats, and a species
of warbler.
The island is covered with a heavy
growth of vegetation. While the monkeys
supplement their diet by foraging on the
vegetation and eating a n occasional insect,
their dietary staple is Purina Monkey Chow.
The chow is distributed at several feeding
stations around the island (fig. 1). A
delayed shipment of monkey chow caused
the July 1968 food shortage and the behavioral changes reported i n this paper.
METHODS
Subjects
On August 4, 1967, the author began a
13 month behavioral study of one of the
seven Cay0 Santiago social groups, group F.
By June 1, 1968, 1454 hours of observation
had been made on the group. An additional
321 hours of observation were made during
June and July 1968 (table 3 ) . Observations were tyDically made from 0730-1145
and 1530-1800 Monday through Friday,
and from 1500-1800 on Saturday and Sunday. During June and July 1968, observations were made on all days except June
AM. J. PHYS.ANTHROP.,33. 263-272
30th. The monkeys were habituated to the
author’s presence, and allowed his close approach.
The Cayo Santiago monkeys are all tattooed for identification of individuals. Censuses of the population begun in the late
1950’s provide the matrilineal relatives of
all but the oldest monkeys. Patrilineal relationships are not known.
Prior to the food shartage, group F contained 69 monkeys (table 1 ). Although the
fourth largest group on the island in numbers, group F was a t least fifth, and probably sixth, in group dominance, and was
repeatedly forced away from feeding stations and rest areas. Although occasionally
able to control a feeder for several minutes
to a n hour. group F usually fed by making
“raids” on temporarily unoccupied feede r ~The
. ~ monkeys would quickly fill mouth
and cheek pouches, and then sprint off into
the undergrowth with a more dominant
group at their heels. The group F monkeys
spent some part of every day foraging, even
when they had already eaten a good deal of
monkey chow.
Food shortage
Provisioned food during June and July
1968 is shown in table 2. The period with1 Present address: 2154 Kennington Road, Knoxville Tennessee 37917.
% T h eC a y 0 Santiago colony is administered by the
Laboratory of Perinatal Physiology, National Institutes
of Health.
3During the entire study, group F was never seen
feeding at F-4.The Small Cay was usually occupied
by grnup A, which contained over 200 monkeys and
was dominant to group F.
263
264
JAMES LOY
out provisioned food of any kind was only
one week. However, from June 24th-29th
the regular provision of 300 pounds of
monkey chow per day was cut to 240
pounds per day. Between July 1st-5th over
2000 mangoes were brought to the island,
and on July 2nd a h a 1 300 pounds of
monkey chow were distributed. Mangoes
were not provided after July 5th. The next
food given to the monkeys was 800 pounds
of whole kernal corn between July 12th14th. On July 15th, monkey chow arrived
at Cayo Santiago, and 300 pounds were
put out. Subsequently, the monkeys received the regular 300 pounds of Purina
chow every day (except Sunday, when no
food was provided). In total, 22 days
elapsed between periods of uninterrupted
D
provisioning with the full complement of
chow-.
Typical behavior. during the transition
period between the birth and
mating seasons
The food shortage occurred during late
June-early July. It thus fell at the end of
the birth season (January-June) and the
beginning of the mating season (JulyDecember) (Koford, '65). At this time
there is much play among infants and
juveniles. Although fertile matings typically do not begin until August, an occasional male-to-female series-mounting is
seen in June and July (possibly with the
motor patterns characteristic of ejaculation). When the animals are well-fed and
relaxed, there is normally a lot of grooming,
sitting close together and sitting in body
contact. The frequency of agonistic interactions is very high. Intergroup and intragroup fights are common, especially around
the feeders.
RESULTS
Group F mortality
Six group F animals died during the food
shortage. They ranged in age from just
over one year to seven years. Five of the
six dead were females (not significantly
different from expected figures; Binomial
test; p = 0.18). One of the dead females
CAY0 SANTIAGO
-
100 Meters
TABLE 2
Provisioned food during June and July 1968
Date
Provisioned food
22 June and prior
300 pounds Purina Monkey
Chow every day (execpt
Sunday)
240 pounds of monkey chow
every day
800 mangoes
300 mangoes; 300 pounds
monkey chow
200 mangoes
None
800 mangoes
None
800 pounds of whole kernel
corn distributed over the
three days
300 pounds Purina Monkey
Chow
None
300 pounds of monkey chow
every day (except Sunday)
South Point
Fig. 1 Map of Cay0 Santiago. Modified from
Altmann ('62). F-1 is no longer used and therefore is not shown on the map.
TABLE 1
1 July
2 July
Age-sex profile of Cayo Santiago group F:
July 1st, 1968
Ace
Male
Female
6 and older
5
11
5
1
3
4
5
5
3
5
5
7
3
4
7
29
40
2
Yearlings
Infants
5
3
2.4-29 June
3 July
4 July
5 July
G 1 1 July
12-14 July
15 July
16 July
17 July and
subsequently
BEHAVIORAL RESPONSES TO FOOD SHORTAGE
suffered from Diabetes menitus, which may
have been exacerbated by the food shortage.
General behavior during the
food shortage
The general activity level of the monkeys
appeared to be depressed during the famine. There was a great increase in the
amount of time spent foraging from the
vegetation cover. Same monkeys, especially
the young, appeared to lose weight. A few
of' the monkeys that subsequently died appeared lethargic immediately before they
were missed from their group. These same
monkeys foraged constantly up to their
death or disappearance. Among the plants
eaten by the group F monkeys during the
food shortage were Roble flowers (Tabeuia
heterophylla), needles of the Australian
pine ( Casuarina equisetifolia), Corcho
leaves and twigs (Torrubia fraguns), Sotacaballo leaves (Randia aculeta), Coconut
palm fronds (COCOS nucifera), and the
fruit and leaves of the Sea Grape (CoccoEoba uvifera). Unfortunately, as emphasis was placed on social behavior, precise, quantitative data with regard to
identity and amount of all plant foods
eaten was not recorded.
The diabetic adult female in group F
w7as observed to eat two lizards on July 5th
(probably Anolis spp.; Heatwole, Sade and
Hildreth, '63). The lizards, each four to
six inches long, were consumed in toto.
Earlier in the spring of 1968, the same female was seen eating a single lizard of
about the same size. This lizard u7as also
entirely consumed, head first. Such carnivorous behavior had never before been observed among the Cay0 Santiago monkeys.
It is not known whether this female's diabetes was connected with her consumption
of animal protein.
Quantitative changes in behavior
During the focd shortage all forms o€
behavior were depressed with the single
exception of foraging (figs. 2-8). The
food shortage data was compared to averages for June 1968, June 16th-30th 1968,
and the combined averages for April, May
and June 1968 (tables 3, 4 ) .
Social grooming (self grooming not included) dropped from the average of 17.7
k
F4
a
B
m
22
2
.n
Qa
265
266
JAMES LOY
episodes/hour in the latter half of June
1968 to 8.4 episodes /hour during the food
shortage (July 1st--1l t h for calculation purposes) (fig. 2 ) . This was a drop of 52.5%.
The same type of drop in frequency of
grooming and other social activities is
often seen on weekends even during normal provisioning (see Sunday, July 21st,
on figs. 2, 3 , 5 , 6). When the chow provided
on Friday and Saturday is exhausted, the
monkeys turn almost exclusively to foraging. The reverse of this situation was seen
on July 2nd. After a two day break in provisioning, distribution of monkey chow resulted in a dramatic rise i n fights, body
contact, and grooming (figs. 2, 3 , 5, 6 ) .
Grooming episodes between relatives
rose from 55.3% of the total June 1968 episodes to 73.9% of the total during the food
shortage, while grooming episodes between
non-relatives dropped from 44.7% to
26.1% of the respective totals for the
same periods.
Body contact per hour (the instances of
2 animals sitting touching each other) decreased slightly, from 6.9 episodes/hour
for June 16th-30th to 6.4 episodes/hour
f o r July 1st-11th (fig. 3 ) . This was a 7.2%
drop. Body contact between relatives rose
from 70.5% of the total during June to
73.9% during the food shortage, while
body contact between non-relatives dropped
TABLE
4
Per cent decreases i n behavior: group F . Expressed as u percentage drop during the period o f
food shortage ( J u l y 1 - 1 1 ) f r o m the time period shown. Example: the average numher of
grooming episodes/hour dropped 52.5% during J u l y 1st-11th from the m e a n of June 7630, 1968.
Grooming/
hour
Body
Contact,
hour
Play/
hour
Fights/
hour
Non-feeder
fights/hour
Displace-
mc::z/
Non-displ.
movements/
hour
%
5%
5%
%
%
7.2
5%
90.n
7%
52.5
52.5
32.3
15.6
33.3
Ave, for April, May
and June 1968
45.8
7.2
90.4
48.1
35.4
30.3
45.4
June 16-30
(L
30-
-30
3
0
I
a
w
a
:20-
-2 0
D
0
v,
a
w
m
z
5
-1 0
10-
0
a
W
-0
0JUNE 16
JULY I
WG. I
Fig. 2 Grooming episodes in group F per hour of observation during June 16-30 and
July 1-31, 1968.
267
BEHAVIORAL RESPONSES TO FOOL) SHORTAGE
from 29.5% to 26.1% of the respective
totals for the two periods.
The number of play episodes decreased
dramatically from 2.51 episodes/hour during June 16th-30th to 0.15 episodes/hour
during July 1st-11th (a drop of 90.0% )
(fig. 4 ) .
Fights, including both inter- and intragroup fights at and away from feeders, €ell
from 6.8 fights/hour in the last half of
June to 3.2 fightsihour during the food
shortage (fig. 5). This was a drop of 52.5%.
Non-feeder fights (those inter- and intragroup fights that occurred away from the
feeding stations) also showed a drop, fallClZ
73
0
NO FOOD
FOOD
I
IH
ClZ
111
a
07
W
ing from 4.2 fights/hour during the latter
part of June to 2.8 fights/hour during the
food shortage (fig. 6 ) . This was a decrease
of 32.3%.
Displacements of group F by other
groups showed little change during the
food shortage. Between June 16th-30th
there were 1.1displacements of group F per
hour; between July 1st-llth, 0.9 clisplacements/hour (drop of 15.6%) (fig. 7).
Neither did the number of times that group
F moved without obviously being displaced
by another group (non-displacement movements) show much change. Group F
moved on its own on the average of 0.9
v///m
FOOD
20-
-20
10-
- 10
0
0
5!?
a
W
I-
2
lz
0
0
>
a
0
m
0--t
20
JUNE 16
10
-0
20
AUG. I
JULY 1
Fig. 3 Body contact episodes i n group F per hour of observation during June 16-30
July 1-31, 1968.
NO FOOD
FOOD
P
3
1
6-
FOOD
1 -6
-5
-4
-3
-2
- I
-0
JUNE
IS-
JULY I
AUG. I
Fig. 4 Play episodes in group F per hour of observation during June 16-30 and July
1-31, 1968.
268
JAMES LOY
times/hour during the latter half of June, total fights ( p < 0.001), and non-feeder
and 0.6 times/hour during the food short- fights ( p < 0.025) for the two periods. The
drops in frequency of body contact ( p >
age (fig. 8). This was a drop of 33.3%.
Even though the mating season was ap- 0.25), displacements of group F by other
proaching, series-mountings of females by groups ( p > O . l O ) , and non-displacement
males decreased from ten in June 1968 to movements ( p > O . O 5 ) were €ound to be
non-significant .
one in July 1968.
The significant decrease in number of
DISCUSSION AND COMPARISONS
fights per hour is no doubt connected to
Several statistical tests of significance the fact that the amount of food provided
were run on the data for June 16th-30th in the feeders went from almost a normal
versus the food shortage data. The “t” test level to no food at all very rapidly. Thererevealed significant decreases between the fore chow was not an incentive for intermean frequencies of grooming episodes or intragroup fights. Also, the monkeys
( p < 0.001), play episodes ( p < O . O O l ) , were widely scattered as they foraged, and
-I5
N O FOOD
FOOD
-to
-5
0--I .)
20
JUNE 16
10
3M
-0
30t
AUG. I
20
JULY I
Fig. 5 Total fights in group F per hour of observation during June 16-30 and July
1-31, 1968.
NO FOOD
FOOD
-9
0
-0
U
-7
- 6
-5
-4
-3
-2
-1
-0
30)
lo
20
30 9
JULY I
AUG. I
Fig. 6 Non-feeder fights in group F per hour of observation during June 16-30 and
July 1-31, 1968.
0-
1.
20
JUNE 16
269
BEHAVIORAL RESPONSES TO FOOD SHORTAGE
there were few squabbles over choice items
of vegetation. If a small amount of
chow had continued to be provided, a
rise in the number of fights per hour might
have been expected to occur.
The relative stability of the frequency of
body contact is related to the stability of intragenealogy activities. During normal provisioning, the percentages of both grooming episodes and body contact episodes are
consistently higher between relatives than
non-relatives (Sade, '65, '66; personal observations). Intragenealogy grooming typically comprises 60-70% of all grooming,
and intragenealogy body contact 70-80 %
20
301
of all episodes of body contact. During the
food shortage, total intergenealogy interactions decreased much more than total intragenealogy interactions. This is seen from
the changes in the percentage of grooming
and body contact between relatives and
non-relatives. The small decrease in intragenealogy activities was not enough to significantly affect the mean number of body
contact episodes per hour. These data reflect the importance of the matriline to
rhesus monkey social organization and behavior (see Sade, '65. '66).
Even though there was no food to prompt
group interactions around the feeders, the
10
JULY I
Fig. 7 Displacements of group F per hour of observation during June 16-30 and July
1-31, 1968.
u)
t-
z
w
E
y
2-
-2
I-
--I
0
x
I-
z
W
r
w
c)
a
-I
a
E
I
0
z
-0
0-
JULY I
Fig. 8 Non-displacement movements by group
16-30 and July 1-31, 1968.
JUNE 16
AUG. I
F per hour of observation during June
270
JAMES LOY
frequency of displacements of group F did various stages of estrus were fairly comnot decrease significantly. This is prob- mon among mainland populations in the
ably explained by ( 1 ) the crowded condi- same area; ( 4 ) no mating, mounting, or
tions on Cay0 Santiago which made it presenting was observed; (5) many of the
practically impossible for any group to animals had the appearance of lethargy;
move without contact with anothcr group and ( 6 ) the number of intragroup squab(and in the case of group F, contact almost bles was reduced.
The above observations closely parallel
always led to displacement), and ( 2 ) the
possibility that during the food shortage those made on group F during the food
the other groups were attracted to the au- shortage. Group F, however, did not split
thor, expecting him to distribute chow. In into foraging sub-groups, probably due to
approaching the author, the other groups the crowded conditions on Cay0 Santiago
would almost certainly have displaced and the need for group unity in intergroup
encounters. The baboon group-split and the
group F.
In general, the group F monkeys were reduction in fighting resembles the situa( 1 ) foraging from the vegetation cover tion on Desecheo Island. The intragenealmuch more than usual during the food ogy unity observed among the rhesus monshortage, ( 2 ) grooming, playing, fighting keys (in grooming and body contact data
and mating much less, and (3) moving on from Cay0 Santiago, and in the compositheir own, being displaced by other groups, tion of some of the sub-groups on Deand sitting in body contact slightly less secheo) suggests that perhaps the small
than usual. Social interactions between foraging parties observed by Hall were
non-related monkeys showed a much composed of related individuals.
Rosenblum, Kaufman and Stynes ('69)
greater decrease in frequency than those
reported on the behavioral effects of brief
between matrilineal relatives.
On Desecheo Island, another NINDS ( 2 day) food deprivation among laboratory
colony on Puerto Rico's west coast, the groups of pigtail macaques (Macaca
rhesus monkeys are unprovisioned and nemestrina) and bonnet macaques ( M a must forage for all of their food among caca radiata). During deprivation the pigplants including grasses, shrubs, herbs, tails showed ( 1 ) marked drops in social
and cactus. Morrison (n.d.) made the fol- play, social grooming and autogrooming,
lowing observations on the Desechco mon- (2) an increase in the amount of motherkeys : ( 1) the original group of monkeys infant contact (during the daylight phase
placed on the island in 1966 (taken from of the experiment), and (3) an increase
1 social group on Cay0 Santiago) has split in foraging through the bedding material.
into structured sub-groups which allow a The bonnets failed to show either a signifimaximum scatter for feeding in the severe cant increase in mother-infant contact or
environment (some, but not all, of these decrease in social grooming during deprivasub-groups appear to consist of related in- tion. Bonnet autogrooming decreased, and
dividuals) ; and (2) grooming, juvenile foraging showed a brief increase. Strangely,
play, and total fighting are much less fre- the bonnet infants showed a slight increase
in social play during the hunger day.
quent than on Cay0 Santiago.
Recognizing the limitations of theorizing
Hall ( ' 6 3 ) reports on the behavior of
chacma baboons (Papio ursinus ) stranded from the small sample presented above, the
on an island in Lake Kariba, Southern Rho- behavioral reaction of Old World monkeys
desia. These animals were subjected to a to food shortage (with some exceptions as
severe shortage of vegetation food items. seen from the data on bonnet macaques)
Hall noted the following: ( 1 ) one or more seems generally characterized by decreasof the groups may have split up into small ing frequencies of almost all social activforaging parties of normally onc, two, or ities (with at least some species showing
three animals; ( 2 ) almost all of the mon- a greater drop in interactions between nonkeys' activity was directed at food-seeking: related animals than between relatives),
( 3 ) not a single female in full- or partial- and a concomitant increase in food-seeking
estrus was observed, although females in activities.
BEHAVIORAL RESPONSES TO FOOD SHORTAGE
ACKNOWLEDGMENTS
The author was supported while on Cay0
Santiago by NSF grant GS-1777 to Dr.
Donald Stone Sade, Northwestern University. Thanks go to Dr. Sade €or his critical
review of the manuscript; Dr. R. E. Myers,
Chief, Laboratory of Perinatal Physiology,
San Juan, Puerto Rico. for permission to
work on Cay0 Santiago; and Dr. John Morrison for his kind permission to use unpublished material from Desecheo Island.
LITERATURE CITED
Altmann, S. A. 1962 A field study of the sociobiology of rhesus monkeys, Macaca mzrlatta.
Ann. N. Y. Acad. Sci., 102: 338-435.
Carpenter, C. R. 1942 Sexual behavior of freeranging rhesus monkeys (Macaca mulatta):
Specimens, procedures and behavorial characteristics of estrus. J. Comp. Psych., 33: 113-142.
Hall, K. R. L. 1963 Variations in the ecology
of the chacma baboon. In: The Primates. J.
27 1
Napier and N. A. Barnicot, eds. The Zoological
Society of London, pp. 1-28.
Heatwole, H., D. S. Sade and R. W. Hildreth 1963
Herpetogeography of Puerto Rico. I. Herpetofauna of Cay0 Santiago and Cay0 Batata. Carib.
J. Sci., 3: 1-5.
Koford, C. B. 1965 Population dynamics of
rhesus monkeys on Cay0 Santiago. In: Primate
Behavior: Field Studies of Monkeys and Apes.
I. DeVore, ed. Holt, Rinehart and Winston, New
York, pp. 160-174.
Morrison, J. (n.d.) Report on present conditions
of rhesus monkeys in Group H at Desecheo
Island and Cayo Santiago, May 27-31, 1968.
Unpub. ms.
Rosenblum, L. A., I. C. Kaufman and A. J. Stynes
1969 Interspecific variations in the effects of
hunger on diurnally varying behavior elements
i n macaques. Brain Behav. Evol., 2: 119-131.
Sade, D. S. 1965 Some aspects of parent-offspring and sibling relations i n a group of rhesus
monkeys, with a discussion of grooming. Am. J.
Phys. Anthrop., 23: 1-1s.
1966 Ontogeny of social relations i n a
group of free-ranging rhesus monkeys (Macaca
mulatta Zimmerman). Unpub. Ph.D. dissertation. University of California, Berkeley.
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