Communication in a Group of Semi-Captive Black Rhino (Diceros Bicornis). A Reconsideration of their Cognition and Social Organization

Many species of perissodactyls  are either extinct or foredoomed [1] Particularly threatened are all 5 species of rhinos, mountain zebra and the four species of tapir. On a positive side, however, the population of Prezwalski horses ( Equus caballus) extinct in the wild in the mid-20th century, has now increased and two “feral” populations have been re-established, ( in Lozere in France, and Mongolia : https://www.fao.org.) 

If we know enough about how to provide a life of quality for rhino, we may be able to stem the tide of extinction,  recognizing the intrinsic rights of individuals [2] and retain each species’ role in the ecological community [3].  Since there are no areas of the world  left unaffected by human activities, all large mammals are subject to some human management. Rhinos are known for having high rates of mortality and low breeding scores in captivity [4] even though their life expectancy in zoos  can be between 30-55 years, if  surviving infancy [5]Black Rhinos ( Diceros bicornis) number  between 3,000 to 5,000, but despite efforts by various organizations ( e.g. Save the Rhino International) they are being poached and shot for human gain (South Africa gave licenses for 10 adult black rhinos to be shot in 2022), and their habitat continues to be usurped by humans as numbers decline.  Detailed behaviour studies are crucial to improve the breeding of black rhino. For example, in this group of Black Rhino, female infertility was found to be the result of management [6]Separating the the females at night, resulted in all females breeding and 13 young  black rhino have been re-introduced to a national park (The History of the breeding of  black rhino at Imire Safari Park Zimbabwe).A detailed study of rhino communication is also of evolutionary interest since there have been few comparative behavioural studies in the perissodactyla. Various “folk beliefs” concerning  black rhinos sensory abilities are widely held. It is commonly believed by  both popular science and serious scientists (e.g. Reed. 2017, How do rhinos communicate? Pets on mom internet, Estes 2012 & rhinosorcecentre.com) that rhinos have poor sight but, there is no physiological evidence for such statements, Pettigrew and Manger (2008) after assessing retinal ganglion cell density, maintain that black rhinos see “at least as well as rabbits and able to define both near and far objects clearly”. Little is known about the rhinos ability to smell, taste or communicate by touch. Olfactory communication is complex [7] and often difficult to identify. But, we do know that black rhinos eat a range of shrubs and herbs and are fussy about what they eat, rejecting unfamiliar foodstuffs [8] so taste must be import to them.

Generally only explicit behaviors are recorded in communication studies. These are divided into  “aggressive”  (threat and attack) and “submissive behaviors” (  withdraw and particular postures). A few studies include affiliative behaviours. A movement or posture which is highly ritualized (exaggerated, and often performed out of context e.g. Huxley 1960) is performed primarily to communicate. However, many non-ritualized  movements  which are used for non-social functions, may be of communicative value. These include ear or tail movements primarily designed to get rid of flies [9], rubbing, touching, scratching self, movements to protect sense organs and other parts of the body. Head and tail elevation (the result of contraction of the anti-gravity muscles in preparation for flight [10] sweating  (to reducing temperature), and noises made without the larynx, such as coughing or sighing to clear the bronchial tract or lungs [11] all these behaviors, can be of communicative significance.

The senses used to communicate vary,  and are often multi-sensory, thus visual messages may also have olfactory, tactile  or gustatory messages. For example “head resting” or “horn to horn” pushing, where the performer and the recipient can see but also touch, smell and possibly taste each other  [12] Auditory communication using the larynx is of particular interest because, unlike other sensory modalities, it has no other function but for communication. It has been known for some decades that the meaning of many, (but not all) calls made by ungulates, canids, and felids are context dependent (Kiley 1972 ), that is they indicate a general level of excitement, but the specific meaning (what emotion is being felt with other information) is gathered from the context.  Although some of the sounds made by black rhino have been recorded, neither their hearing nor the frequency or complexity of their calls have been investigate in any detail [13] Today  although there is much equipment and many techniques for investigating audition [14] this study only records sounds heard by the observing humans.The frequency of interactions would be expected to be higher in larger groups, so black rhino who are often found alone or with their previous offspring, are considered  “less social” than white rhino (Diceros bicornis), but the degree of sociality is also influence by the size of the population. It is believed that black rhino (Diceros bicornis) evolved to be predominantly browsers since  they eat a large range of tree and bushes leaves and twigs [15] and because their browse is erratically distributed, they live in small groups. Whereas white rhino (Ceratotherium simum), with their large flat top lip, are believed to be predominantly grazers and consequently can live in larger groups. But, the etho-ecology of any species is also the result of individual experiences, we now know that both species can adapt to a wide range of habitats and types of social living. For example, black rhino, can live in open Savannah as well as the Namibian deserts (e.g. https://www.savetherhino.org/programmes/ministry-of-environment-and-tourism/ ), and have been filmed in groups of up to 50  (BBC 2005) and have long been known to come together in groups of 10 or more [16] The degree of sociality is the result of the environment, population density  and individual experiences rather than just species typical.

Since  resources (e.g.food, water, shelter, resting sites etc.) are equally available to all in many large  grazing herbivores, they do not need to compete constantly for resources as do some birds and primates where resources are batched and restricted. There may be no need for a “dominance hierarchy” to reduce injuries [17] rather the great advantage of social  living is to gather ecological and social information. As a result, their social networking may be based on cooperation accompanied by knowledge of others’ roles and skills rather than competitive. This has been shown in buffalo  [18,19] This study assessed:-

1) the use of the different sensory modalities in communication.  

2) The meaning of different behaviors in communication (their message-meaning)

3) Their overall social organization (without  giving individual personality profiles).  

In a study  of this group of bak rhino in their night time accommodation where only 1 female was breeding, a change of management resulted in all 4 females breed and 13 black rhino raised and re-introduced to a National Park ( Randle & Kiley-Worthington 1996 and Imire  Safari Park: The History of the Black Rhino  2022). This indicates that communication studies may be crucial for survival.

Many of the behaviors recorded have not previously been recorded or their meaning assessed, but this has led to a re-construct of their social contract, emphasizing cooperation  ( see e.g Rubenstein et Kealey 2010).

Zimbabwe National Parks Authority captured seven black rhino as infants (4 females and 3 male aged 1- 6 months old) when their mothers were poached during the 1990’s . They were given to Imire Wildlife Park to rear. They were bottle reared and lived in a group under guard ranging over the 1,000 h nature reserve during the day. At night they were herded into an enclosure fortified against poachers, the females into individual stables, the males kept in a group as showin in (Table 1).

Table 1: The observed rhinos ages and sex.

All the rhino were continuously observed during the day in the nature reserve from a distance between 5 m and 50 m for 257 hours per rhino (1800 rhino hours)  by 7 observers. Each observer observed one rhino and rotated between rhinos each day. The observers were their keepers and guards, and had spend at least 2 years daily with the rhino. Each rhino was easily identify at over 100m and could be approach to within  2m without moving. The observers were supplied with binoculars and given 15 hours training before the data was used. The observations were recorded either verbally onto a tape recorder, or onto a psion event recorder and transferred to a computer for analyzes. At all times the observations were monitored by two experienced observational ethologists.

Forty one behaviors were recorded. Every behaviour was defined, their definitions given in (Table 2). 

The  performance (P) and the responses (RR) to each behavior was recorded. The response was only recorded if it occurred within 5 seconds of the performer’s directed behaviour, thus  communication dyads - performer and recipient response - were recorded, not chains.  Should the recipients response initiate another behaviour from the initial performer,  after a further 5 seconds; it was  recorded as a separate interaction.

If the recipient to which the behaviour was clearly directed, showed no response within 10secs, the response (RR) was recorded as “ignore”. Several behaviors were often performed  and recorded simultaneously.

Since the population was small and behavioural variation high, an assessment of averages and percentages are preferred to detailed statistical analysis as the intention is to outline the methodology and trends, although some excel, t and x squared tests have been used (Table 2). 

Table 2: The behaviors recorded , their definitions and the categories into which they were placed ( see below for explanation of the categories).

1206 interactions recorded between the 7 rhino continuously observed with more than one behaviour recorded in many  interactions.

1) The use of the different  sensory modalities in communication.

 The frequency the different sensory modalities were use is in (table 3). 

Table 3: The frequency the different sensory modalities were used in interactions by both by  the  performer and  by the response of the recipient. 

Of the 83.2% visual messages, an unknown percentage were combined with olfaction, and  a further 11%  of the visual messages could have a touch and taste content, thus the total percentage of the messages with a visual content was 95%.  Only  5.7% of the messages were auditory. Auditory messages using the larynx (vocalizations) consisted of growl, grunt and squeak were rare ( table 4). Non-vocalized noises were more common (e.g. blow, cough, snort, and sigh).  It is possible that there were also ultra or infra sounds given. 

Table 4: The frequency the different auditory messages were used (see table 2 for definitions). 

The two most frequent noises were “cough” given with an open mouth,  and “blow”, made by pressure changes in the buccal and nasal cavities with the mouth shut. 

2) The meaning of the messages.

The meaning of many messages  is “explicit”, that is self-evident. For example: “running away”  indicates the recipient wants to get away from the initiator. Touching or licking another indicates is affiliative. 

But, the meaning of some behaviors is “implicit “, that is  it does not have self-evident motivational, state such as “tail wagging” or “head shaking” often related to indecision/ uncertainty whether to approach or avoid  [20] or frustration ( an inability to obtain a desired goal [21,25] When given in social situations, they are called  “displacement activities” . They are:- tail wag, flap both ears, ear twitching, head or body shake or nodding, head toss, head extended forwards, scratch or rubbing self, chewing  ( table 2 for definitions). Displacement activities may be exaggerated when ritualized  and occur out of the normal context in communication ( for example preening in courtship in birds Huxley (1960) or head shaking, scratching & tail swishing in ungulates and canids (Kiley-Worthington 1969) where higher priority behaviors are blocked so behaviors of less importance in the repertoire become “disinhibited”, implying that the individual is “uncertain” what to do.  “Uncertain” behaviors were  recorded 202 times; 13.7%  of all the behaviors in interactions, considerably more than aggression or threat. 

The  frequency of the different behaviours in each  of the  7 category of meaning, either performed (P) or as a response,(RR) are shown in (table 5). The overall frequency for each behavioural category (P+RR) in column 4, and its percentage of the total in column 5, and each discussed below. 

Table 5: The frequency of the behaviors in the 7 categories. 

Approach 

(walking or running for at least 4 meters towards another), before negative (aggressive) or positive (affiliative) interaction. The negative responses to approach where infrequent (withdrawal + aggression 27 =6.7% of all : (Table 6). 

Affiliation was ( 72 of 429) 16% of total, but, 31% of  the total approaches were ignored.  

Table 6: Responses to approach 

Uncertain   

Table 5 shows that uncertain behaviors are more frequent as a recipient response than performed by the initiator (Table 5, RR=118  to  P=85).

But, they are one of the least ignored of categories of behaviour ( see table 7 below) indicating their importance in carrying a message.  

Positive interaction 

• Interest 

Interest is shown by explicit orientating and showing curiosity towards the other such as pricking both ears, turning the head  towards, or watching/ looking at the other.  When the attention was directed behind,  one or both ears rotated back, or when the head or tail were raised indicating slight arousal [26-29] are included here. This category is 10.1% of all the behaviors in interactions. More “interest”  is performed by the performer than the recipient. 

• Affiliation 

Affiliation is another explicit behaviour indicating that the individual wants / likes to be close to the other shown by touching, smelling, licking or rub another, contact walking, stand together, following, resting head/chin/neck  on  the other, nose to nose smelling, or standing over another when s/he is lying. It was  22% of the total behaviors recorded, and more frequently performed by the performer  than as a response [30,31]

  The the total positive/ cooperative communicative behaviors is 32 % of all behaviors (10.1 interest +22.4 affiliation). 

Negative interactions 

• Aggression and threat 

Aggressive acts were horn to horn or horn to body push.  Ritualized threat was both ears rotated flat back , or the lowering  of the head with chin withdrawn which pointed the horns at the other. Chasing another, kicking, or turning the quarters towards another or showing intention to kick, were included

Aggression or threat occurred in 3.6% of the behaviors recorded in interactions with little difference between the frequency shown by initiator or responder ( table 5). 

Avoid another or withdrawing as a response 

These accounted for 13.8% of the total behaviours, more common as a response ( withdrawing rather than avoiding).  

The socially negative behaviours are often used to measure  “dominance hierarchy”.  Here they  are considerably less frequent than the socially positive behaviors: 17.4%,  compare to 32.4% 

Ignoring directed behavior 

One of the surprising results was that 41.9% of the directed behaviour was ignored. Further analysis in (table 7). 

Table 7: The frequency  of  the behaviors in the different behavioral categories that were ignored by the recipient 

The most frequently ignored behaviours were: approach, withdraw and affiliative behaviour.

The lease ignored, and the least  used  were aggression and threat  (1.9%).

But, “uncertain” behaviour was not frequently ignored… only 6.1%. This confirms that such behaviour has considerable communicative importance. 

Reciprocity 

Kingsley (1893, anonymous 1993) in his moral children’s tale for children called this  “do as you would be done by”.  The overall frequency of the  recipients response being in the same category as s/he had received was 17.24% (significant  higher than expected at p>0.01). 

Table 8: “Do as Done By” or Reciprocity. The frequent of the response in the same behavioural category as received.

Since 17 incidences of aggression was horn to horn pushing which by definition is reciprocal, aggression is  more than 50% reciprocated. The next highest percentage of the responses that were reciprocated in the same category was “uncertain”, another  indication  that these behaviors have a message value.

The use of the different sensory modalities in communication between black rhino

Since all movements and postures potentially carry messages when individuals can be seen, it is not surprising that visual signals were most common, [23,24]  over over 90% having a visual component, although some of these also carried olfactory or tactile messages. Some visual signals were ritualized such as “head extending forwards”, (indicating curiosity and non-aggression in many large ungulates)  and “ear flattening”, exaggerated in species without temporal horns where the ears are more conspicuous ( Kiley 1969). Although a considerable number of signals were purely visual, many messages were multi-sensory [32-36] 

Auditory communication within the range of human hearing was less common ( 5%).  Noises made without the larynx, characteristic of some arousal, were more common ( Kiley 1972).The use of infra- or ultra- sound in black rhino awaits investigation.

It is concluded that visual communication is used mostly when  black rhino are in a group  and consequently,  they must be able to see quite well.  

The meaning of messages; a re-consideration of the rhinos’ social contract 

 Positive communication, that is  the performance of behaviors leading to group cohesion were categorized into “showing interest” and “affiliation” and were twice as frequent as socially negative communication such as aggression, threatening, avoiding and withdrawing .

Behaviour which has been shown to indicate “uncertainty” and /or frustration, was common in interactions.  Uncertainty can aid the cohesion of the group by reducing potential conflict. This illustrates that rhino make conscious decisions being aware of the other individual and  uncertain whether to avoid or approach [37,38]The situation also allows for the continuation of the status quo, by  messages being ignored so  by the recipient  which was common ( 41.9% of behaviors), another mechanism to decrease conflict and encourage group cohesion.

Reciprocity with a behaviour in the same meaning  category as that received, has not been recorded previously. It was high :17.24%, for the 6 behavioural categories p<0.01).This indicates that  (a)  socially positive reciprocity help cement bonds, and (b) the importance of obeying the social contract with socially negative behavior [39-42]

 Where resources are widely dispersed, social cohesive behaviors, and behaviors likely to reduce conflict or encourage a continuation of the status quo are likely to be more important than conflicts [43-45] although  this will vary with the environment Having a stable cohesive group  is encouraged by bonded individuals,  Socially cohesive behaviors such as affiliation, reciprocity and ignoring behaviors likely to give rise to conflict, have not been previously considered in large herbivores although central to the accumulation of ecological knowledge  (e.g. knowing what to eat and where to find it, where to shelter, drink, the geography of the home area etc ).

 It is important for the individual to learn who to learn from, that is to “know what another knows”, thus, learning  and following youngsters who have less knowledge is not reliable .Further studies on positive behaviors, uncertainty, reciprocity and ignoring directed behaviors in interactions could lead to a more thorough understanding of group organization and cognition in large herbivores ( see also Bordley 1993), but, time is running out for the black rhino who may become extinct before this is done.

All these rhino were shot by poachers in 2007 .However they had, by that time, produced 13 offspring many of whom have been re-introduced to the wild, although it is not known how many of them have survived. The remaining 3 black rhino descendants have bred, and recently have been joined by a pair of breeding white rhino at Imire Wildlife Reserve.  It must be emphasized that this is one of the very few remaining small populations of black rhino who are successfully reproducing in  semi-captivity.

Norman Travers (now diseased) allowed us to conduct this and other studies at Imire in 1994-6. The Travers family have supported our research at Imire in many ways  since, particular thanks go to Judy Travers, the present “matriarch”.  The rhino keepers at Imire who shared the observations are deeply thanked for their dedication and enthusiasm, and Hayley Randle for her assistance during the observations and the first analysis of the data.

There was no external funding, no competing interests, and no animal was caused to suffer as a result of the study.

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