Representational signalling in birds

Biology Letters, Feb 2007

Some animals give specific calls when they discover food or detect a particular type of predator. Companions respond with food-searching behaviour or by adopting appropriate escape responses. These signals thus seem to denote objects in the environment, but this specific mechanism has only been demonstrated for monkey alarm calls. We manipulated whether fowl (Gallus gallus) had recently found a small quantity of preferred food and then tested for a specific interaction between this event and their subsequent response to playback of food calls. In one treatment, food calls thus potentially provided information about the immediate environment, while in the other the putative message was redundant with individual experience. Food calls evoked substrate searching, but only if the hens had not recently discovered food. An identical manipulation had no effect on responses to an acoustically matched control call. These results show that chicken food calls are representational signals: they stimulate retrieval of information about a class of external events. This is the first such demonstration for any non-primate species. Representational signalling is hence more taxonomically widespread than has previously been thought, suggesting that it may be the product of common social factors, rather than an attribute of a particular phylogenetic lineage.

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Representational signalling in birds

Christopher S Evans Linda Evans Receive free email alerts when new articles cite this article - sign up in the box at the top right-hand corner of the article or click here References Email alerting service To subscribe to Biol. Lett. go to: http://rsbl.royalsocietypublishing.org/subscriptions Biol. Lett. (2007) 3, 811 doi:10.1098/rsbl.2006.0561 Published online 14 November 2006 Representational signalling in birds Christopher S. Evans* and Linda Evans Centre for the Integrative Study of Animal Behaviour, Macquarie University, Sydney, New South Wales 2109, Australia *Author for correspondence (). Some animals give specific calls when they discover food or detect a particular type of predator. Companions respond with food-searching behaviour or by adopting appropriate escape responses. These signals thus seem to denote objects in the environment, but this specific mechanism has only been demonstrated for monkey alarm calls. We manipulated whether fowl (Gallus gallus) had recently found a small quantity of preferred food and then tested for a specific interaction between this event and their subsequent response to playback of food calls. In one treatment, food calls thus potentially provided information about the immediate environment, while in the other the putative message was redundant with individual experience. Food calls evoked substrate searching, but only if the hens had not recently discovered food. An identical manipulation had no effect on responses to an acoustically matched control call. These results show that chicken food calls are representational signals: they stimulate retrieval of information about a class of external events. This is the first such demonstration for any non-primate species. Representational signalling is hence more taxonomically widespread than has previously been thought, suggesting that it may be the product of common social factors, rather than an attribute of a particular phylogenetic lineage. 1. INTRODUCTION Some animal calls have the unusual property of seeming to denote environmental events. Such referential signals are produced in response to specific stimuli (e.g. approach of a particular predator and discovery of food) and are sufficient to evoke from companions the full suite of appropriate responses (e.g. adaptive escape behaviour and food search). Given the cognitive sophistication implied by such systems, it was logical for initial research to concentrate on non-human primates, beginning with vervet monkeys (Cercopithecus aethiops; Seyfarth et al. 1980). A flurry of recent papers has revealed that referential signalling may be relatively widespread. For example, it is also present in other cercopithecines (Zuberbu hler 2000a,b, 2001), tufted capuchins (Cebus apella nigritus; Di Bitetti 2003), lemurs (Macedonia 1990), at least one non-primate mammal (suricates (Suricata suricatta); Manser 2001; Electronic supplementary material is available at http://dx.doi.org/ 10.1098/rsbl.2006.0561 or via http://www.journals.royalsoc.ac.uk. Manser et al. 2001) and several species of birds, including fowl (Evans et al. 1993; Evans & Marler 1994; Evans & Evans 1999), ravens (Bugnyar et al. 2001), yellow warblers (Dendroica petechia; Gill & Sealy 2004) and black-capped chickadees (Poecile atricapilla; Templeton et al. 2005). Referential signalling is controversial because it potentially extends the parallels between animal communication and language (Hauser 1996; Evans 1997; Fitch 2005), long considered the principal exception to an otherwise clear pattern of evolutionary continuity (Darwin 1871). Some linguists accept that there is evidence for a primitive type of reference in animal communication (Bickerton 1990; Pinker 1994); others stress the apparent lack of volitional control and conclude that such analogies are not compelling (Lieberman 1994). Similarly, some biologists have objected that referential signals may reveal only the subsequent behaviour of the sender (Smith 1991) or that it is not useful to think of animal signals as containing information at all (Owings & Morton 1998). In sum, conventional studies of call production and playback experiments can establish only that animals behave as if their signals describe external events. The central issue in this debate is both straightforward and empirically accessible: it concerns the cognitive processes that must be invoked to explain the observed pattern of receiver behaviour. Words derive their meaning from mental representations that correspond to stimulus categories. If referential signals and language are truly analogous, then they should similarly evoke representations of the eliciting event (i.e. stimulate retrieval of stored information that then determines receiver response). This property would correspond to Gallistels nominal representation (1990), which is the lowest level of cognitive complexity: it would establish that calls stand for something in the environment. The design of most previous st (...truncated)


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Christopher S Evans, Linda Evans. Representational signalling in birds, Biology Letters, 2007, pp. 8-11, 3/1, DOI: 10.1098/rsbl.2006.0561