Birds often live in environments with multiple types of risks such as predators (Caro ).
To survive predation hazards that vary based on predator attributes, birds have evolved a sophisticated communication system using alarm calls that may show discrete variations (different call types), graded variations (number of sound elements such as note number and calling rate, or finer acoustic features of an element such as call length, frequency/pitch, and relative amplitude), and combinatorial variations (combination of notes or calls).
In this review, I explore the existing evidence for referential signaling in birds and highlight the importance of the cognitive approach to animal communication research.
I hope this review will promote further investigations of alarm-calling behavior in birds and will help enhance our understanding of the ecology and evolution of semantic communication.) and not to refer to objects or events in the environment.
Playbacks of discrete alarm calls elicited qualitatively different behaviors, as if actual predators were present nearby: monkeys ran up a tree for leopard alarms, looked up in the air for eagle alarms, and stood up bipedally for snake alarms (Seyfarth et al. This was the first evidence that vocalizations of non-human primates can refer to external objects and convey this information to receivers.
Here, I treat the term “information” as a reduction of uncertainty in the receivers, as this terminology does not contradict the mathematical models of information theory (Shannon ).
Frameworks for the study of semantic communication about external objects or events.
The functionally referential framework a only considers the association between production specificity and perception specificity as information transmission, whereas the cognitive framework b assumes mental representations of external entities in information processing ), these animals often produce different alarm calls for a variety of predators, and some of them can transmit many different types of information to receivers.
Although the underlying mental processes of signal production and perception were unclear, researchers suggested the idea of “functional reference”, which provisionally referred to the signals that appear to convey information about external referents rather than the change in internal states of the senders.
Macedonia and Evans () proposed two key criteria to classify animal signals as functionally referential: (i) production specificity, which considers the degree to which a signal is associated with a specific external stimulus, and (ii) perception specificity, which considers the degree to which a signal elicits a specific response in the receivers (Fig. To explore production specificity, researchers have tried to show different stimuli (such as different predators and food) to a focal individual and analyzed the association between the external stimuli and the acoustic variation in vocalizations (Evans ).