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A preliminary analysis of wound care and other-regarding behavior in wild chimpanzees at Ngogo, Kibale National Park, Uganda

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Abstract

Caring for others is a key feature of human behavior. Mothers, fathers, siblings, grandparents, and other group members provide care in the form of provisioning, protection, and first aid. To what extent is other-regarding behavior present in our primate relatives? Here we describe an unusual incident of other-regarding behavior toward an injured juvenile female chimpanzee (Pan troglodytes schweinfurthii) at Ngogo in Kibale National Park, Uganda. After the juvenile received a mild head wound from an adult female, several adolescent and juvenile chimpanzees gathered to touch, lick, and peer at the wound. One adolescent male wiped a leaf across the cut. Another adolescent male later groomed the injured female and briefly carried her. Across a 5-year period, we observed only three other instances of other-directed wound care in chimpanzees, occurring in 4% (4/100) of cases in which we observed individuals with fresh wounds, and 57 other instances of allomaternal carrying. Despite the infrequency of such behaviors, our study adds another chimpanzee field site to the list of those where other-directed wound care has been observed. Observations from wild chimpanzees provide insight into empathy and may inform our understanding of the evolution of other-regarding behavior in humans.
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Primates (2021) 62:697–702
https://doi.org/10.1007/s10329-021-00925-7
NEWS ANDPERSPECTIVES
A preliminary analysis ofwound care andother‑regarding behavior
inwild chimpanzees atNgogo, Kibale National Park, Uganda
IsabelleR.Clark1 · AaronA.Sandel1· RachnaB.Reddy2,3· KevinE.Langergraber4,5
Received: 20 October 2020 / Accepted: 10 June 2021 / Published online: 1 July 2021
© Japan Monkey Centre 2021
Abstract
Caring for others is a key feature of human behavior. Mothers, fathers, siblings, grandparents, and other group members
provide care in the form of provisioning, protection, and first aid. To what extent is other-regarding behavior present in our
primate relatives? Here we describe an unusual incident of other-regarding behavior toward an injured juvenile female chim-
panzee (Pan troglodytes schweinfurthii) at Ngogo in Kibale National Park, Uganda. After the juvenile received a mild head
wound from an adult female, several adolescent and juvenile chimpanzees gathered to touch, lick, and peer at the wound.
One adolescent male wiped a leaf across the cut. Another adolescent male later groomed the injured female and briefly
carried her. Across a 5-year period, we observed only three other instances of other-directed wound care in chimpanzees,
occurring in 4% (4/100) of cases in which we observed individuals with fresh wounds, and 57 other instances of allomaternal
carrying. Despite the infrequency of such behaviors, our study adds another chimpanzee field site to the list of those where
other-directed wound care has been observed. Observations from wild chimpanzees provide insight into empathy and may
inform our understanding of the evolution of other-regarding behavior in humans.
Keywords Pan troglodytes· Injury· Alloparenting· Infant carrying· Empathy
Introduction
In humans, help from others in the form of care and provi-
sioning is key for recovering from illness and injury (Gurven
etal. 2000; Kaplan etal. 2000; Sugiyama 2004). Although
caregiving and other-regarding preferences may be most
extensive in humans, precursors of these behaviors can be
found in other animals (Hart 2011; Preston 2013). Caregiv-
ing behaviors such as carrying, provisioning, grooming, and
agonistic support have been observed in one of our closest
relatives, chimpanzees (Pan troglodytes), including toward
vulnerable young whose mothers are ill (Uehara and Nyundo
1983; Huffman and Seifu 1989), injured (Pruetz 2011), or
deceased (Hobaiter etal. 2014; Nakamura and Hosaka 2015;
Reddy and Mitani 2019; Samuni etal. 2019). Chimpanzees
occasionally attend to the wounds of groupmates, including
removing splinters in captivity (Köhler 1925; Yerkes 1943)
and grooming or licking wounds in the wild (Goodall 1983,
1986; Boesch 1991). Whether wound care behaviors actu-
ally benefit the wounded individual remains uncertain, but
licking may promote healing and seems to reflect an other-
regarding impulse (Dittus and Ratnayeke 1989; Boesch
1991). In rare instances, wound care involves tool use:
two juvenile male chimpanzees at Gombe, Tanzania, used
leaves to wipe the wounds of their infant sibling and mother,
respectively (Goodall 1986). Reports of wound care among
wild chimpanzees have been largely limited to maternal kin
(Goodall 1983, 1986), although wound care of genetically
unrelated individuals has been observed in western chim-
panzees at Taï, Côte D’Ivoire, where predation pressure and
social cohesion are elevated (Boesch 1991). Here we report
an unusual case of other-directed wound care involving sev-
eral chimpanzees and a juvenile female at Ngogo in Kibale
* Isabelle R. Clark
isabelle.clark@utexas.edu
1 Department ofAnthropology, University ofTexas atAustin,
2201 Speedway Stop C3200, Austin, TX78712, USA
2 Department ofAnthropology, University ofMichigan,
AnnArbor, MI, USA
3 Department ofHuman Evolutionary Biology, Harvard
University, Cambridge, MA, USA
4 School ofHuman Evolution andSocial Change, Arizona
State University, Tempe, AZ, USA
5 Institute ofHuman Origins, Arizona State University, Tempe,
AZ, USA
698 Primates (2021) 62:697–702
1 3
National Park, Uganda. We provide context by summarizing
wound care behaviors and instances of allomaternal carry-
ing at Ngogo.
Methods
Study site andsubjects
We studied the Ngogo chimpanzees in Kibale National
Park, Uganda, from 2014 to 2019. The population fluctu-
ated between 181 and 219 individuals. Age classes were
defined as follows: infant (0–5 years, until weaning),
juvenile (5–9years), adolescent (nulliparous females of
9–14years; males of 9–15years, based on the size of exter-
nal genitals; Goodall 1983), and adult (parous females and
nulliparous females over 14years; males over 15years).
Non-natal females are estimated to be 13years old at the
time of immigration (Wood etal. 2017). Birth dates are
known to within one day to three months for individuals
born at Ngogo since 1995 and are estimated for older adults
based on physical features and genetic relationships (Wood
etal. 2017). Genealogies have been previously established
from genetic data (Langergraber etal. 2007). Individuals
are considered "unrelated" if they are not parent-offspring,
maternal/paternal siblings, or related through parents’ sib-
lings (e.g., "first cousins," "aunt-niece"), although they may
be more distantly related.
Behavioral observations
We recorded wound care behavior and allomaternal car-
rying adlibitum during one- to three-hour-long continu-
ous focal follows (Altmann 1974) of adolescent and adult
males or during general observations of individuals of all
ages and sexes outside of focal follows (N = 256 individuals,
mean ± SD = 222.67 ± 213.16 contact hours per individual).
AAS collected data during three field seasons (August 24,
2014 to August 30, 2015; October 16, 2017 to June 5, 2018;
June 1 to November 7, 2019). RBR collected data during
four field seasons (May 22 to August 19, 2015; June 24,
2016 to August 12, 2017; May 18 to June 8, 2018; July 17 to
July 28, 2019). IRC collected data during two field seasons
(February 24 to June 3, 2018; January 19 to June 3, 2019).
We recorded all occurrences of open wounds includ-
ing small cuts, lacerations, and puncture wounds. In many
cases, it was unclear how recently injury had occurred. We
report only wounds that appeared relatively fresh (open
and bloody) and count each wound once, regardless of the
total number of days the wound was observed. We excluded
healed scabs, scars, and other injuries that did not include
open wounds. We recorded self-directed and other-directed
wound care behaviors including touching/grooming, licking,
or wiping the wound with leaves ("leaf-dabbing": Whiten
etal. 1999). We defined allomaternal carrying as ventral or
dorsal carrying by a non-mother, considering only bouts that
lasted for two strides or more, including during travel as well
as play (Nishida 1983; Nishida etal. 1999).
Results
Case study
On May 31, 2018, we observed an unusual case of other-
regarding behavior in which multiple chimpanzees pro-
vided care to a wounded juvenile female, Septima (5.5years
old). At 11:05, adult female Bacall (with a clinging infant)
grabbed and pulled Septima’s head, leaving a small but
bloody wound on her forehead (Fig. 1a). Adult male
Fig. 1 a Septima (5.5-year-old female) with minor forehead wound
inflicted by parous female, b Etta (7-year-old female; center) sniffs
and licks the leaves that Damien (12-year-old male; left) used to
wipe the forehead wound of Septima (right; lying down), c YoYo
(12.5-year-old male) carries Septima ventrally after hearing other
groupmates hunting nearby
699Primates (2021) 62:697–702
1 3
Garrison (Septima’s biological father) positioned him-
self between Septima and Bacall, who sat 2m from each
other. Bacall and Garrison moved out of view, while Sep-
tima moved a few meters before laying with her stomach
on the ground, still alert and responsive. Septima’s mother,
Dahlia, and infant sister, Hermione (1.5years old), were not
in visible range but were observed earlier and later in the
day, indicating that they may have been in the party, which
was large and spread out. Septima usually traveled with her
mother and maternal siblings.
Most members of the party began to travel at 11:15,
but Septima remained with several chimpanzees including
Damien (12-year-old male), Etta (7years, Damiens mater-
nal sister), Joya (7-year-old female), and Bach (9.5-year-old
male); notably, all four of these individuals are orphans and
genetically unrelated to Septima. Adolescent male Damien
approached Septima and brushed an overhanging cluster
of leaves across her wound, sniffing and licking the leaves.
Juvenile female Etta sniffed and licked the same leaves
(Fig.1b), touched the wound with her fingers, licked her
fingers, and licked the wound directly (see Online Resource
1 for video). Juvenile female Joya peered, her face within
10cm of Septima’s head. Adolescent male Bach approached
to sniff and possibly lick the wound. When they all began to
travel, Septima followed Damien and embraced him ventro-
ventrally. Septima did not appear to have trouble walking.
We lost sight of Septima until 12:00, when she was
observed following Buckner (18.5-year-old male) and his
maternal brother, Holland (8years)—also orphans and
unrelated to Septima. Around 12:30, YoYo (12.5years,
paternal brother of Septima and maternal brother of Joya)
groomed Septima, including her wound. Joya and Sanger
(10years, Septima’s maternal sister) approached to peer
at the wound. As they peered, Septima touched the wound
herself and licked her fingers repeatedly. Septima followed
YoYo when he began to travel, but both stopped after only
several meters while the rest of the group, including Sep-
tima’s sister, moved on. Septima reached both arms toward
YoYo and he embraced her ventro-ventrally, thrust briefly,
then continued to intermittently embrace, groom, and play
with her while lying down. At 12:52, YoYo moved as if to
travel but sat back down less than a meter from Septima,
who remained lying on the ground, and gently poked her
twice. She whimpered and did not move, and YoYo returned
to grooming her.
At 13:00, following a total of 30 minutes of grooming and
resting in close proximity, YoYo and Septima sat up as other
group members began hunting a duiker within audible range.
YoYo began to move toward their vocalizations, Septima
whimpered, and YoYo repeatedly turned back to reach for
her. When the duiker began to make alarm calls, they both
became alert and YoYo picked up Septima, stood bipedally,
and held her briefly as she clung to him ventrally (Fig.1c;
see Online Resource 2 for video). She fell off when YoYo
returned to all fours. YoYo attempted to move past Septima
but, when she began screaming, reached back and pulled her
to him. They embraced for three seconds, but Septima fell
off again when YoYo began to run. He paused to look over
his shoulder when she began screaming again while follow-
ing him. They ran out of view, and Septima was not seen for
the remainder of the day. In the following days, Septima was
back with her mother without signs of injury.
Other cases ofwound care
During a 5-year period, we observed chimpanzees with
fresh wounds on 100 occasions (Table1). In 29% of these
instances, we observed self-directed wound care. Almost
half (13/29) of these cases included tool-assisted wiping
of wounds using leaves, or "leaf-dabbing" (Whiten etal.
1999). At least four of these 13 tool-assisted cases also
involved self-grooming and licking. The other 16 cases
were not tool-assisted and involved only self-grooming or
licking. Wounded individuals received care from others for
4% (4/100) of the wounds we observed, including the case
study reported above. We describe the three other cases of
other-directed wound care in brief.
On March 9, 2017, RBR found adolescent male PeeWee
(11years) grooming the wounds of an older, genetically unre-
lated male, Barron (16years). Barron’s ear was bleeding and
split into two pieces, the inside of his elbow was wounded and
bleeding, and he avoided putting weight on his hand, which
hung limp from his wrist. We did not observe how Barron
acquired these injuries. PeeWee groomed the bloody spots on
Barron’s elbow and ear, holding one piece of the ear in each of
his own hands as he peered down the center of the split. While
this pair is not genetically related, they exhibited a strong
social bond (Reddy and Mitani 2019; Sandel etal. 2020). Later
in the day, Barron was observed to alternate between touching
his own ear wound and licking his fingers repeatedly.
Table 1 Number of wounds (N = 100) for which individuals engaged
in self-directed care in the form of (1) leaf-dabbing, which was some-
times accompanied by grooming/licking, and (2) only grooming/lick-
ing, and for which wounded individuals received these forms of care
from other groupmates
In three of the of the four wound cases in which we observed other-
directed care, we also observed the wounded individual licking their
own wounds
Self-directed Other-directed
Maternally
unrelated
Maternal kin
Leaf-dab 13 1 0
Groom/lick 13 1 2
Total 26 2 2
700 Primates (2021) 62:697–702
1 3
On July 5, 2017, RBR observed adult female Bacall
inspect and groom a cut on the hand of her adolescent son,
Williams (10years). Williams may have received the injury
in an aggressive interaction with another adult female, as he
was lunging toward this female and screaming when Bacall
ran toward him. Bacall’s first action was toward the injury,
rather than toward the other female or reassuring Williams.
Bacall picked up Williams’ arm by the wrist, pulled it toward
her, and peered at the wound before grooming it with her
fingers and mouth.
On January 25, 2018, AAS observed juvenile male Hol-
land (7.5years) groom and lick a puncture wound on the
arm of his older, young adult maternal brother, Buckner
(18years). Buckner likely received this injury during an
aggressive encounter with conspecifics the previous day
(Sandel and Watts 2021). He was observed to self-groom
and lick his wound immediately prior to Holland’s care.
Although there is a large age gap between this maternal sib-
ling pair, and Buckner had already traveled independently
from their mother for much of Holland’s life, the pair’s rates
of association, proximity, grooming, reassurance, and travel
vigilance increased dramatically after their mother died in
2017, prior to this incident (Reddy and Mitani 2019).
Other cases ofallomaternal carrying
We observed 58 cases of allomaternal carrying of 26 infants
and only one young juvenile (Septima, described above) by
34 individuals. Fourteen of the 26 infants were carried only
once, and the other 12 were carried multiple times, some by
multiple individuals. Half of our observations involved close
maternal kin (29/58, all siblings except for two instances in
which a juvenile male carried his maternal sister’s infant),
and the rest involved individuals that were not maternally
related, though one case involved paternal siblings and
several cases involved individuals that were more distantly
related on the paternal side. The majority of carrying epi-
sodes were brief and not repeated, often occurring in the
context of play or travel. Carrying occasionally occurred
in response to the distress of the individual carried, as in
Septima’s case. In another instance, we observed an immi-
grant female retrieve and carry an infant back to his mother,
after he cried as researchers approached the sapling he was
playing in alone. We also observed a young adult male twice
carry his infant brother, whose mother’s ability to travel was
hindered by a missing foot from a past snare injury.
Discussion
We observed an unusual case of other-regarding behavior
toward an injured juvenile female chimpanzee. An adoles-
cent male wiped her wound with leaves, a juvenile female
touched and licked the wound, and another adolescent male
groomed and briefly carried her. Wound care of others
appears to be rare among chimpanzees at Ngogo (Table1).
We observed only three additional instances of other-
directed wound care, representing 4% of observed wounds
during this period. In contrast, we observed self-directed
wound care for 29% of wounds. Given that we did not
observe the infliction of wounds in most cases and did not
continuously follow wounded individuals, these results may
underestimate the prevalence of both self- and other-directed
wound care. We also observed 57 additional instances of
allomaternal carrying, but unlike the carrying that occurred
during the case study, no other instance was associated with
an injured group member.
The case of Septima was a rare example of tool-assisted,
other-directed wound care. Self-directed "leaf-dabbing" of
wounds has previously been reported at Ngogo and other
chimpanzee sites (Goodall 1983; Whiten etal. 1999; Sanz
and Morgan 2007; Watts 2008). The extension of this behav-
ior to others has only been reported among two pairs of
maternally related chimpanzees in the wild (Goodall 1986).
More broadly, previous reports of wound care have either
been limited to mothers and offspring (Goodall 1983, 1986)
or occurred among genetically unrelated chimpanzees
in West Africa, where heightened predation pressure and
social cohesion may facilitate cooperation among non-kin
(Boesch 1991). There is no leopard predation at Ngogo.
While the three other cases of wound care we observed
occurred between mother and son, maternal brothers, and a
pair of genetically unrelated adolescent males with a strong
social bond (Reddy and Mitani 2019; Sandel etal. 2020),
Septima’s caretakers were not maternal relatives nor close
social affiliates of hers. Their other-regarding behaviors may
have been activated by her distress (Preston 2013; de Waal
and Preston 2017), which was made apparent by her lying
prostrate on the ground, whimpering, and screaming.
Although the wound itself appeared to be relatively
minor, multiple unrelated individuals tended to Septima,
including two adolescent males. Male chimpanzees do not
typically provide parental care, as females mate with multi-
ple males and paternity is uncertain. However, male chim-
panzees have been observed to carry infants for extended
periods (Notman and Munn 2003; Pruetz 2011; Cibot
etal. 2019), provide care to their orphaned younger sib-
lings (Hobaiter etal. 2014; Reddy and Mitani 2019), and
adopt related as well as unrelated orphaned infants (Boesch
etal. 2010; Samuni etal. 2019). Given that both adolescent
males described here were among those observed to care for
their younger siblings following maternal death (Reddy and
Mitani 2019), they may have been predisposed to providing
care to Septima, as prior experience seems to augment the
empathic response (reviewed by Preston and de Waal 2002).
Most of the individuals who attended to her were orphans,
701Primates (2021) 62:697–702
1 3
suggesting that maternal loss itself may have enhanced their
perspective-taking ability toward Septimas distress in the
absence of her mother.
The benefits of wound care behaviors in nonhuman pri-
mates remain to be studied. Grooming may remove dirt
particles, and licking is thought to facilitate wound healing
given the antibacterial properties of saliva (Dittus and Rat-
nayeke 1989; Hart and Powell 1990; Boesch 1991). Leaf-
dabbing of wounds may reduce infection risk compared to
direct contact, or it may be more akin to the exploratory
touching and probing of novel objects such as carcasses
(e.g., Cronin etal. 2011). Experimental evidence shows that
chimpanzees are attuned to images of wounded conspecifics
and experience negative arousal in response to prosthetic
wounds on a familiar human experimenter, suggesting that
they empathize with injured others (Sato etal. 2019). This
attention to and curiosity about wounds may lead to wound
care of others under certain conditions, such as signs of dis-
tress or the presence of a strong social bond. Thus, regard-
less of how beneficial wound care is, attention to wounds
may represent an empathetic precursor of human-like proso-
ciality, for which there is increasing evidence of in social
mammals like apes (Warneken etal. 2007; Yamamoto etal.
2009; Melis etal. 2011). While allomaternal care is rare
among chimpanzees, we found that wound care and car-
rying sometimes occur even among non-kin. The question
should no longer be whether chimpanzees have the capacity
for other-regarding preferences, but how socio-ecological
and demographic factors drive variation in the expression
of prosocial behaviors across individuals and populations.
Supplementary Information The online version contains supplemen-
tary material available at https:// doi. org/ 10. 1007/ s10329- 021- 00925-7.
Acknowledgements We thank the Uganda Wildlife Authority, the
Uganda National Council for Science and Technology, and the Mak-
erere University Biological Field Station for permission to conduct
research. For support in the field, we are grateful to John Mitani, David
Watts, Samuel Angedakin, Alfred Tumusiime, Ambrose Twineomu-
juni, Brian Kamugyisha, Charles Birungi, Chris Aliganyira, Diana
Kanweri, Godfrey Mbabazi, and Lawrence Ndangizi. Funding was
provided by the Leakey Foundation, the University of Michigan, the
Nacey-Maggioncalda Foundation, the National Science Foundation
(1540259, F031543, BCS-1613392, DGE-1256260), and the National
Geographic Society (CRE-9742-15).
Declarations
Conflict of Interest The authors declare that they have no conflicts of
interest.
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The Chimpanzees of the Taï Forest - edited by Christophe Boesch November 2019
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