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Pyow-hack revisited: Two analyses of Putty-nosed monkey alarm calls
Male Putty-nosed monkeys have two main alarm calls, pyows and hacks. While pyows have a broad distribution suggestive of a general call, hacks are often indicative of eagles. In a series of articles, Arnold and Zuberbuhler showed that Putty-nosed monkeys sometimes produce distinct pyow-hack sequences made of a small number of pyows followed by a small number of hacks; and that these are predictive of group movement. Arnold and Zuberbuhler claimed that pyow-hack sequences are syntactically combinatorial but not semantically compositional because their meaning cannot be derived from the meanings of their component parts. We compare two theories of this phenomenon. One formalizes and modifies the non-compositional theory. The other presents a semantically compositional alternative based on weak meanings for pyow ('general alarm') and hack (non-ground movement'), combined with pragmatic principles of competition; a crucial one is an 'Urgency Principle' whereby calls that provide information about the nature/location of a threat must come before calls that do not. Semantically, pyow-hack sequences are compatible with any kind of situation involving (moving) aerial predators or (arboreal) movement of the monkeys themselves. But in the former case, hacks provide information about the location of a threat, and hence should appear at the beginning of sequences. As a result, pyow-hack sequences can only be used for non-threat related situations involving movement, hence a possible inference that they involve group movement. Without adjudicating the debate, we argue that a formal analysis can help clarify competing theories and derive new predictions that might decide between them. (C) 2016 Published by Elsevier B.V.
Female Putty-Nosed Monkeys Use Experimentally Altered Contextual Information to Disambiguate the Cause of Male Alarm Calls
Many animal vocal signals are given in a wide range of contexts which can sometimes have little in common. Yet, to respond adaptively, listeners must find ways to identify the cause of a signal, or at least rule out alternatives. Here, we investigate the nature of this process in putty-nosed monkeys, a forest primate. In this species, adult males have a very restricted repertoire of vocalizations which are given in response to a wide variety of events occurring under conditions of limited visibility. We carried out a series of field playback experiments on females (N = 6) in a habituated group in Gashaka Gumti National Park, Nigeria, in which male alarm/loud calls were presented either alone, or following acoustic information that simulated the occurrence of natural disturbances. We demonstrate that listeners appear to integrate contextual information in order to distinguish among possible causes of calls. We conclude that, in many cases, pragmatic aspects of communication play a crucial role in call interpretation and place a premium on listeners' abilities to integrate information from different sources.
A forest monkey’s alarm call series to predator models
Some non-human primates produce acoustically distinct alarm calls to different predators, such as eagles or leopards. Recipients respond to these calls as if they have seen the actual predator, which has led to the notion of functionally referential alarm calls. However, in a previous study with free-ranging putty-nosed monkeys (Cercopithecus nictitans martini), we demonstrated that callers produced two acoustically distinct alarm calls to eagle shrieks and leopard growls, but both alarm calls were given to both predators. We can think of two basic explanations for this surprising result, a methodological and theoretical one. Firstly, acoustic predator models may not always be suitable to test alarm call behaviour in primates, sometimes causing uncharacteristic behaviour. Secondly, referential alarm calling may not be a universal feature of primate alarm call systems. Considering the methodological and theoretical importance of these possibilities, we conducted a follow-up study using life-sized leopard, eagle, and human models on the same population and compared the resulting vocal responses to those given to acoustic predator models. We compared the alarm call series given to each of these predator model types and found a considerable degree of consistency suggesting that the mode of presentation did not affect anti-predator calling strategies. However, evidence for audience effects on calling behaviour was inconclusive. While it appears that predator class is reliably encoded by different call series types irrespective of the mode of presentation, observations of these same call series given in non-predatory contexts indicate that predator class is unlikely to be the relevant organising principle underlying the alarm-calling behaviour in this species. We conclude by offering an alternative, non-referential, account of the alarmcalling system exhibited by this species.
Monkey semantics: two 'dialects' of Campbell's monkey alarm calls
We develop a formal semantic analysis of the alarm calls used by Campbell's monkeys in the Tai forest (Ivory Coast) and on Tiwai island (Sierra Leone)-two sites that differ in the main predators that the monkeys are exposed to (eagles on Tiwai vs. eagles and leopards in Tai). Building on data discussed in Ouattara et al. (PLoS ONE 4(11):e7808, 2009a; PNAS 106(51): 22026-22031, 2009b and Arnold et al. (Population differences in wild Campbell's monkeys alarm call use, 2013), we argue that on both sites alarm calls include the roots krak and hok, which can optionally be affixed with -oo, a kind of attenuating suffix; in addition, sentences can start with boom boom, which indicates that the context is not one of predation. In line with Arnold et al., we show that the meaning of the roots is not quite the same in Tai and on Tiwai: krak often functions as a leopard alarm call in Tai, but as a general alarm call on Tiwai. We develop models based on a compositional semantics in which concatenation is interpreted as conjunction, roots have lexical meanings, -oo is an attenuating suffix, and an all-purpose alarm parameter is raised with each individual call. The first model accounts for the difference between Tai and Tiwai by way of different lexical entries for krak. The second model gives the same underspecified entry to krak in both locations (= general alarm call), but it makes use of a competition mechanism akin to scalar implicatures. In Tai, strengthening yields a meaning equivalent to non-aerial dangerous predator and turns out to single out leopards. On Tiwai, strengthening yields a nearly contradictory meaning due to the absence of ground predators, and only the unstrengthened meaning is used.
Call combinations in monkeys: compositional or idiomatic expressions?
Syntax is widely considered the feature that most decisively sets human language apart from other natural communication systems. Animal vocalisations are generally considered to be holistic with few examples of utterances meaning something other than the sum of their parts. Previously, we have shown that male putty-nosed monkeys produce call series consisting of two call types in response to different events. They can also be combined into short sequences that convey a different message from those conveyed by either call type alone. Here, we investigate whether 'pyow-hack' sequences are compositional in that the individual calls contribute to their overall meaning. However, the monkeys behaved as if they perceived the sequence as an idiomatic expression rather than decoding the sequence. Nonetheless, while this communication system lacks the generative power of syntax it enables callers to increase the number of messages that can be conveyed by a small and innate call repertoire.
Primate Pragmatics: Female Putty-Nosed Monkeys Use Contextual Information to Disambiguate the Cause of Male Alarm Calls
Pyow but not hack calls of the male putty-nosed monkey (Cercopithcus nictitans) convey information about caller identity
Individual differences within the acoustic structure of vocalisations have the potential to inform signal receivers about the identity of the caller. Such differences can often be explained by morphological differences of the signaller’s sound production apparatus. Natural selection may have favoured individual variation within call types, especially if identity cues enhance call function. In addition, animals may modify their vocalisations such that they sound more similar to, or more distinct from those of neighbouring conspecifics. We recorded pyow and hack vocalisations from five recognised male putty-nosed monkeys (Cercopithecus nictitans) in Gashaka Gumti National Park, Nigeria. We analysed the temporal and spectral features of both call types to investigate whether the calls contained identity cues, and whether calls of neighbouring males were less or more different in their acoustic structure than expected by chance. More parameters were found to vary significantly between individuals within pyows than hacks, and whilst pyows could be correctly assigned to individual callers more often than would have been expected by chance, hacks could not. We found no relation between geographic distance and acoustic similarity of pyows and hacks.