Essay on Contemporary Issues in Ethology: Variation among Mammalian Alarm Call Systems and the Problem of Meaning in Animal Signals

Abstract

Understanding the information conveyed by animal signals requires studies of both production and perception. It is important to determine the relationship between signal morphology and the circumstances of production, the way signaller behavior varies with motivational state and the role of context in mediating responses to signals. Alarm calls are well‐suited to research of this type because they are widespread in birds and mammals and typically evoke unambiguous responses. We review studies of alarm calling in primates and ground‐dwelling sciurid rodents, concentrating especially on whether these signal systems may be viewed as ‘functionally referential’, that is, as conveying sufficient information about an event for receivers to select appropriate responses. Comparisons of the physical, behavioral and habitat characteristics of these species suggest that incompatibility of the escape responses required to avoid different classes of predators may have been an important factor in the evolution of functionally referential alarm calls.

The central importance of information in studies of animal communication

“…In California ground squirrels, Spermophilus beecheyi, acoustically different alarm calls encode information about urgency, but not predator type (Owings & Hennessy 1984); in primates, they encode information about different predators (vervet monkeys, Chlorocebus aethiops: Seyfarth et al 1980; Diana monkeys, Cercopithecus diana: Zuberbühler et al 1999). Macedonia & Evans (1993) discuss the evolution of alarm call systems that encode different types of information. Finally, in addition to their acoustically different alarm calls for ground and aerial predators , domestic chickens, Gallus gallus domesticus, produce food calls that signal the presence of food.…”

The alarm call system of female Campbell's monkeys

“…According to Macedonia & Evans (1993), a signal qualifies as 'referential' if all eliciting stimuli belong to a common category (e.g. 'leopard' or 'ground predator') and if the signal alone is sufficient to trigger appropriate responses.…”

Predator-deterring alarm call sequences in Guereza colobus monkeys are meaningful to conspecifics

“…In our case, we assumed that initial gaze responses were consistent across all group members, irrespective of age/sex class, as the different hunting behaviours of eagles and leopards are likely to generate different expectations in the monkeys (cf. Macedonia & Evans 1993). We expected that eagle-related stimuli would trigger a higher proportion of upward gazes than leopard-related stimuli, and vice versa, in line with the predators' most likely direction of attack.…”

“…Some prey species respond with distinct alarm calls to the behaviour of the predator, such as the speed of its approach (Griesser 2008). As a consequence, identical signals can be produced in response to a variety of predators, allowing recipients to make inferences about the degree of danger and urgency of response (Robinson 1980;Macedonia & Evans 1993;Blumstein 1995). In contrast, some other species, such as East African vervet monkeys, Cercopithecus aethiops, produce discrete alarm calls to distinct predator types.…”

“…Such observations are interesting from an evolutionary perspective because of the parallels with symbolic reference in human language (e.g. Seyfarth et al 1980;Macedonia & Evans 1993).…”