natural communication of animals and the range of studies devoted to learning whether animals, namely apes, can acquire language under human tutelage

natural communication of animals and the range of studies devoted to learning whether animals, namely apes, can acquire language under human tutelage

There is a distinction to be made between the natural communication of animals and the range of studies devoted to learning whether animals, namely apes, can acquire language under human tutelage (Hayes & Hayes, 1951; Kellogg & Kellogg, 1967; Terrace, 1985; Savage-Rumbaugh & Lewin, 1994). Vicki, a chimpanzee raised by Keith and Catherine Hayes (1951), demonstrated an ability to vocalise a few words (Mama, Papa and cup). Notably though, these utterances lacked clarity and were facilitated by the use of her hands to control her lips. Similar studies have shown that human speech is beyond the capabilities of animals (Kellogg & Kellogg, 1967). Consequently, it was questioned whether or not chimpanzees have the required neuromuscular structures to produce human speech (Lieberman, 1968).

Chimpanzees; Nim Chimpsky and Washoe however, have shown the ability to understand and produce fragments of American Sign Language (ASL) when taught (Terrace, 1985; Gardener & Gardener, 1971). They demonstrated they could acquire up to one-hundred and twenty-five signs. However, their abilities were limited to the combination of two to three words and researchers argued that this did not amount to language as they could not form the word-strings syntactically; as humans do (Terrace, 1985). Kanzi, a bonobo raised by Duane and Sue Savage-Rumbaugh, communicated with those around him using a keyboard of lexigrams (symbols) and mastered the use of over two-hundred signs (Savage-Rumbaugh & Lewin, 1994). Notably, these examples merely reflected the equivalent ability of a two or three year old human; who continually develop a recursive grammar far beyond that of their distant ancestors (Limber, 1980).  Recognition of these limitations has led to a growth of research analysing the properties of animals’ natural vocal communication and questioning whether these can be characterised as ‘language’. Language, in this review, will thus be defined by several key components (as approved by Dr. Katie Slocombe, 2013); whether it is learned, intended, flexible, and ‘functionally referential’ and lastly, whether it follows a grammatical structure or syntax.

In humans, the argument whether language is an innate faculty or a socially learned phenomenon, naturally extends to consider animal communication too. For some species the vocalisations of infants appear fully formed and acoustically similar to those generated by adults (e.g. Vervet monkeys) (Seyfarth & Cheney, 1986). Their infant alarm calls are almost as effective as those given by adult species in provoking an escape response from conspecifics nearby. This suggests that the production of vocalisations is largely innate or progresses extremely early in their development. Relatedly, primates raised in isolation or with foster mothers of a different species (squirrel and vervet monkeys) still produce species-typical vocalisations (Winter, Handley, Ploog and Schott, 1973; Herzog & Hopf, 1983; Owren, Dieter, Seyfarth & Cheney, 1993). This again stresses the importance of genetic factors and highlights the limited effect of auditory experience (learning).

The study of songbirds, however, shows that when reared in isolation from adult song, they generated abnormal, or ‘isolate’, versions (Thorpe, 1958). The creation and practice of species-atypical signals (“raspberries” and extended grunts in captive chimpanzees) could indicate that animals have a generative capacity comparable with human language (Hopkins, Taglialatela & Leavens, 2007), though such overtly atypical signs are infrequent within natural habitats. Alternatively, this could imply that calls must be socially learned. The role of social learning is discussed in relation to acoustic variation in animal vocalisations. The ability to modify the acoustic structure of a vocalisation as a result of experience is termed ‘vocal learning’ (Janik & Slater, 2000).This has been previously shown in cats (Molliver, 1963) and rhesus monkeys (Sutton, Larson, Taylor & Lindeman, 1973) although it required training. Research without such has indicated that calls can be subjected to social learning pressures and become group specific; demonstrated by humpback whales (Payne & Payne, 1985) and parrots (Wright & Wilkinson, 2001). The pant-hoot’ calls of chimpanzees, dissimilar in neighbouring communities, are thought to be actively modified as neither habitat or genetic difference accounted for the disparity; providing further support for the vocal learning hypothesis (Crockford, Herbinger, Vigilant & Boesch, 2004).

A questionable feature of language amongst animals is the intention with which calls are made to conspecific listeners. Original thought (Darwin, 1872) contended that animal sounds were involuntary consequences of bodily actions and the effort exerted on their muscles. In time, these particular sounds, Darwin felt, became synonymous with specific emotions like pain or rage. Some contemporary opinion has maintained the notion that animal vocalisations are principally an external expression of internal states of emotion; “…quite automatic and impossible to suppress” (Bickerton, 1990, pg. 142). This concept of reflexive vocalisation is disputed by evidence demonstrating that animals are able to selectively call. Budgerigars modified the features of their song depending on the reward received (Manabe, Staddon & Cleaveland, 1997). Calls were used deceptively by swallows as a paternity guard (Moller, 1990) and by capuchin monkeys to gain competitive advantage for food (Wheeler, 2009). However, calling to express certain information (food or predation) does not necessarily demonstrate an intention to communicate with a selected conspecific. Seyfarth and Cheney (1986) reported that inaccurate avian-predator calls (when spotting a pigeon rather than an eagle), made by infant vervet monkeys, caused adults to look up yet rarely give alarm calls of their own. Notably, when infant calls were accurate, the adult proceeded to make another call regardless. The authors concluded that they did not produce these calls in response to their perception of another’s ignorance or need for information. Recognition of the call, yet failure to correct the infant implies that the information was accurately obtained, but the intention to communicate with the infant specifically; was absent (Seyfarth & Cheney, 2003).

Flexibility is another necessary characteristic for the characterisation of language.  Nonhuman primates have shown the ability to produce a structurally unique sequence of calls that are context specific (Zuberbuhler, 2002; Outtara, Lemasson & Zuberbuhler, 2009a, Candiotti, Zuberbuhler & Lemasson, 2012). Grey-cheeked mangabeys produce lower- frequency calls in order to communicate between groups (as the sound travels longer distances) whereas within group communication merely warrants a typical ‘scream’ call (Waser & Waser, 1977). The control of vocalisations indicates their use of such calls is flexible and serves a multitude of purposes. Red-bellied tamarins increase their rate of food calls depending on whether other group members are present (Caine, Addington & Winddfelder, 1995). Meerkats exhibit this variation dependent on whom the call is addressed to, and questionably; on the motivational state of the caller (Townsend, Rasmussen, Clutton-Brock & Manser, 2012). Moreover, the probability of producing ‘flee’ alarms was increased in line with the urgency of the predation instance. Similar conclusions on predation pressures have been reached within the monkey population (Stephan & Zuberbuhler, 2008). The authors imply that primate species with an extensive number of threats would intuitively produce a greater repertoire of calls. Dominance and submission are also contended to play a role within vocal flexibility for chimpanzees (Slocombe, Kaller, Call, Zuberbuhler, 2010). It has been argued that semantically specific acoustic variation during call production is functionally equivalent to suffixation in human language (Outtara, lemasson & Zuberbuhler, 2009b)

Frequent animal studies have established that vocalisations alone can provoke an appropriate response from conspecific listeners (Seyfarth, Cheney & Marler, 1980; Zuberbühler, 2000, 2001; Arnold & Zuberbühler, 2006; Pereira & Macedonia, 1990). In this sense, communication is ‘functionally referential’.  These ‘functionally referential’ vocal signals can elicit specific adaptive responses from listeners (i.e. avoiding predation) and can be context-specific (i.e. discerning between different species).  A typical example is the vervet monkey; able to produce acoustically distinct calls, each narrowly associated with a particular predator (Struhsaker, 1967). Utilising such information, researchers were able to show that these calls do not require actual visual recognition of the predator; instead species produced a response from mere playback of the alarm call it is associated with. The monkeys typically ran into trees for leopard alarms, looked down for snake alarms and upwards for eagle alarms (Seyfarth, Cheney & Marler, 1980).  These responses were observed as though the distinct acoustic qualities of each call specified different external objects or events. Following such findings, this research has been replicated with several other primates; Diana monkeys, Campbell’s monkeys, putty-nosed monkeys and ring-tailed lemurs. Again, unique calls habitually distinguished between avian and ground-based predators (Zuberbühler, 2000, 2001; Arnold & Zuberbühler, 2006; Pereira & Macedonia, 1990).

Functionally referential calls are not limited to predation; they can be relevant for food sources also. The most convincing findings to date have stemmed from the study of fowl (Evans & Evans, 1999); male chickens fashioned characteristic ‘food’ calls upon discovering edible objects. Similarly, marmosets displayed an increased number of feeding-related behaviours when their food-related calls were played (Kitzmann & Caine, 2009). More recently, this type of research has been conducted on chimpanzees. They searched a greater number of locations, and for a longer duration of time when grunts related to bread rather than apple; indicating an ability to distinguish between calls and, arguably, between the subsequent foods (Slocombe & Zuberbuhler, 2010). It does, however, remain unclear what the precise nature of the calls’ referents are. These grunts, or equivalent vocalisations in other animals, could label food as good or bad. Alternatively, they could refer to the specific food presented. Pessimistic thought would contend it may only communicate that food is present without reference to type or quantity (Clay, Smith & Blumstein, 2012).

The last component of language to be scrutinised is syntax; a set of grammatical rules governing our use of words in speech and written language. Its use, within humans, seems simple. However, its role in animal communication appears more imperfect.

More broadly defined, syntax has been interpreted to consider the combinatory use of animal calls (Marler & Tenaza, 1977). It is argued that primate vocalisations can be perceived as discrete signals (Fischer, 1998) that, under this comprehensive definition, could signify syntactic ability.  Contemporary research readily uses syntax as a way of characterising studied patterns of vocalisations from several species that appear to follow a consistent structure or show meaning (semantics) within their calls. Birdsong was primarily considered to possess this particular property (Kroodsma & Miller, 1982).  Since; bats (Bohn, Schmidt-French, Schwartz, Smotherman & Pollak, 2009), killer whales (Shapiro, Tyack & Seneff, 2010), hyraxes ((Kershenbaum, Ilany, Blaustein & Geffen, 2012) and some primates (Zuberbuhler, 2002; Clarke, Reichard & Zuberbuhler, 2006) have displayed combinatorial abilities. It is universally accepted though, that call combinations used by any animal are unlikely to approach the level of complexity shown in human language (Jackendoff, 1999; Bickerton, 2003; Fitch & Hauser, 2004). This particularly applies to recursion; the limitless nature of embedding sentences within sentences.

Ultimately, for animal communication to be considered ‘language’ they must demonstrate that their vocalisation are both learned and intended, can provoke a specific response from another, can adjust its use to mean several things and further, and ultimately organise their calls into a structure.

Focus of Investigation

The topic of this investigation is language and communication within animals; explicitly determining whether or not their vocalisations within their natural habitat can be defined as language. The film being studied stems from the organisation, Earth Touch; who specialise is capturing numerous animal species in their natural habitats across the world. The video was then made available for public access on YouTube. Titled; ‘Animal altercation! Angry monkeys chase off a leopard’, the video lasts approximately four minutes long, having been recorded on the 7^th January, 2010. The scene depicts vervet monkeys and baboons’ responses to the presence of a leopard within their surroundings. It begins with a demonstration of vervet monkey alarm calls, followed by vocalisations given by the baboons. As the video progresses we see the leopard flee his position (a tree); chased out by the baboon troop. The final minute shows the leopard thirty minutes after the original altercation, yet focus will be placed on the initial interaction for the benefit of this analysis. The chosen clip simply aims to show the public this particular interaction for entertainment purposes and is described by Earth Touch cameraman, Graham Springer; commentating on proceedings.

The video captures several displays of animal vocalisation given by two different species; both associated with predator alarm calls. The video will be examined for such instances and the possibility to interpret such displays as ‘language’. The criteria for ‘language’ outlined by Dr. Katie Slocombe (2013), and explained previously, will shape my interpretation and analysis to ascertain whether it is reasonable to conclude that language exists in animals.

Interpretation and analysis

The limitations of nonhuman communication are clarified by existing literature detailing attempts to replicate human speech (Kellogg & Kellogg, 1967) and the construction of word-strings using forms of sign language (Gardener & Gardener, 1971). Intuitively, it seems obvious to discern the prospect of ‘language’ from a setting in which animals freely communicate without human influence. Consequently, it has become imperative and popular to study animal communication within their natural environments.

In accordance with Seyfarth, Cheney and Marler’s (1980) research, the use of a species-specific alarm calls is evident within this film. The initial, short and sharp vocalisations observed within the video are akin, if not identical, to the barking ‘hacks’ identified by Struhsaker (1967). Likewise, constant visual focus towards the leopard implies that these calls explicitly corresponded to the identification of this predator. Conversely, these vocalisations did not resemble the short, double-syllable ‘cough’ sound attributed to eagle sightings or the ‘chutter’ alarm synonymous with snakes; their other typical threats. The archetypal response (running into the trees; Seyfarth, Cheney & Marler, 1980) was not required assumedly due to the lack of immediate danger and existing position of the monkeys. Interestingly, vocalisations continued despite this.

Whether the observed communication is characteristic of functionally referential calls is debatable as it did not require a specific response from a conspecific listener. However, this does not rule out the existence of this property of language, it merely reflects the context-specific nature of its necessity.  Given the concealed nature of the leopard (hidden amongst foliage in a tree), it could be reasonably inferred that not all vervet monkeys had visual confirmation of the leopard’s presence and consequently the secondary calls heard are arguably an adaptive response to a situation. They have no knowledge of a threat but the call allows them to model their behaviours accordingly.

Nevertheless, the reciprocal calls given by other vervets nearby exemplify the function of these barks as transmitters of information that listeners are able to decode and extract meaning from. As Hauser (1996) would testify; this is a basic aspect of vocal communication. Furthermore, their replication of seemingly identical sounds would suggest that this call is consistently used across the vervet monkey population.

Noticeably, in these instances when the calls were both visible and audible, the monkey’s line of sight was focussed towards the leopard. This is consistent when the baboon begins to vocalise also. Given this  (and that calls remain acoustically similar), one could infer, as Seyfarth and Cheney (2003) do; that the alarm calls are not intended for a particular conspecific but rather is designed to inform those close by.

A noticeable feature of the vervet monkey’s alarm call was the distinct sequences in which the smaller units of sound were composed. A ‘sequence’ was coded by the continuous nature of the vocalisation. The short barking sound, referred to previously, is first sounded alone yet it is quickly followed by a pair of identical barks, then in four part combination and once more in a threesome. This could be interpreted as four separately distinct sequences, or alternatively, as one. Subsequently, the calls (in sequence) may reflect the syntax.

At worst, the prevalence of these examples in typical vocalisations indicates that call combinations are an important aspect of animal communication, as previously thought (Crockford & Boesch, 2005). Interestingly, the specific call seems consistent in its acoustic quality for the duration of the sequences, although this obviously cannot be verified here. Such an observation could advocate a combinatorial method of expression, rather than the development of an acoustically unique vocalisation, in order to affect the meaning of the call.

This could have evolutionary relevance, as vocal repertoires would not be expected to develop in terms of novel sounds but by linking existing ones. This though, was previously demonstrated with the combination of acoustically different calls (e.g. ‘whoop-gobble’; Waser, 1975). Distinctively, this example displays the use of acoustically identical calls in compositional variation. This could potentially refer to another aspect of the situation, i.e. the urgency of threat (Townsend et al., 2012; Stephan & Zuberbuhler, 2008). The lack of urgency in this case (leopard wanting to sleep, not feed) could model such a relationship.

The presence of vocalisations that are ‘learned’ is limited if not non-existent. A tenuous prediction was proposed that baboons may have socially learned the semantic specificity of vervet monkey calls and consequently approached the leopard in support.

The introduction of the baboon troop could signify that they understood the calls of the vervet monkey to some extent. In this sense, the video gives an example of social exchange of information between two different species and subsequently advocates the role of social learning at some point within this specific environment. This inference is contentious given that we are visually restricted. We are unable to see the behaviours shown from the baboons’ original location.

Recommendations and Conclusion

The video offers complementary evidence to past research within the field of animal communication. However it is not a comprehensive example of all five features of language defined previously.

Clear evidence of species-specific predator alarm calls were observed, associated with the notion that animals demonstrate acoustically specific vocalisations related to a particular threat (Seyfarth, Cheney & Marler, 1980). Whilst these have commonly indicated animal communication can be both flexible and ‘functional referential’, the content of the video ensures that only limited conclusions can be drawn. Firstly, given that the call produced was expressly designed for the presence of a particular predator (leopard), there is little evidence of variation or flexibility. We can only imply that different calls would be made in other contexts as we were purely witness to one circumstance. This suggests that a number of videos displaying a range of vocalisation (e.g. food-related and other predator-based calls) are necessary for verification of this language component. Similarly, we were prevented from observing whether or not the vocalisation elicited a specific adaptive response (running into trees) from listeners due to the context of the situation (monkeys were already positioned in the tree). As such, this vocal display provides partial evidence for animal communication being ‘functionally referential’.

The presence of vocalisations that are ‘learned’ is limited if not non-existent. A tenuous prediction was proposed that baboons may have socially learned the semantic specificity of vervet monkey calls and consequently approached the leopard in support. However, this remains inconclusive. Critically considered, the video also provides an incomplete account of ‘intentional’ communication. Whilst the specificity of the alarm call demonstrates an intention to convey a particular message, we cannot conclude with authority that these calls are directed towards the species in general, or particular group members. However, this question is left unanswered by wider research, thus it could be ambitious to believe one video may provide a solution. For now, this aspect of language remains predominantly unique to humans. The video shows us an example of the combinatorial ability of vervet monkeys and their calls; from which hesitant support for the emergence of syntax use is inferred. However, this must be considered with the broadest of definitions (Marler, 1977) and clearly inferior to human ability (Bickerton, 2003).

For an improved, more overt indication of such language components, a broad sample of videos would be beneficial. The context-specific nature of calls requires a wide-ranging collection of examples to verify the vocal variability and intention animals display.  The phenomena of social learning demands a longitudinal study of behaviours from which any alterations can best be documented. Even so, a comparison with genetic evidence is still essential to discern whether their abilities are innate or otherwise. Conclusions from this evidence would be strengthened by the introduction of resources that help quantify their effects. For example, sound equipment to accurately detect differences in the acoustic quality of the animal calls would aid our understanding of how units of sound are combined, and consequently, whether rules are used by animals in sequence construction (syntax). Ultimately, the field would be hard-pressed to locate footage which can span the range of circumstances necessary for validation of all five features of language. A meta-analysis is most applicable for this objective.

Reflection

A structured method of analysis was conducted in order to eradicate potentially biasing effects. The initial analysis of the video was restricted to instances of vocal behaviour; systematically ignoring behaviours that were gestural by nature, unless seemingly relative to the vocalisations. Contextual information i.e. line of sight, was noted where appropriate. Classification of animal ‘language’ as outlined by Slocombe (2013) was subsequently applied to these cases and, if deemed relevant, implemented into a final analysis. Disregard for gestural behaviours meant that there must be behavioural displays that were inevitably overlooked, however, explicitly searching for vocal references avoids the potential for confounding information between the two and discussing features that are altogether unrelated to language. The contribution of a subjective narrative throughout the footage would typically have a biasing influence. However, his [Graham Springer’s] comments were limited to discussing overt behaviours rather than making inferential propositions; merely explaining that “…they [vervet monkeys] were looking downwards” or “…[the leopard] only occasionally looked to see where all the noise was coming from”, for example. Therefore, his impact may be restricted.

However, interpretational analysis is unavoidably jeopardised by the personal expertise and knowledge of those conducting it. Conclusions derived from the recording are likely to suffer from inaccuracies and could demonstrate a level of naivety given my novice ability in the field of animal communication. Similarly, important features of the video may have been unnoticed or discounted within the initial coding process.  Due to our evolutionary lineage, and our relation to apes, our tendency to impose human characteristics onto animal behaviour potentially dilutes the realistic interpretation of communication. Humans perhaps seem determined to discover language amongst animals.

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