Communication Theories - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 83

the right prey is selected and every other organism is excluded. An insectivore bird,
for example, has a codified (cognitive template) image of its prey.
A food specialist has a restricted repertoire of “cognitive templates,” which
allows it to conserve energy, whereas a generalist has a more broad collection of
templates and wastes much energy in random attempts. The dance of honeybees is
an example of codification about food source and abundance.
More complex codes are requested to optimize the search for resources. In
addition to the codes for recognizing a prey, for example, there are codes for
identifying the suitable environment in which to search for a prey. To every
resource is associated a spatial configuration that is a carrier of meaning [see the
theory of the eco-field (Farina and Belgrano 2006 )] which must be recognized.
Today, the degradation of the ecological codes and the changes in the environ-
mental conditions in which codes have evolved are crucial issues in the challenge to
preserve biodiversity and the associated ecological processes.
The acoustic codes are units of informational acoustics carried out by special
organs (e.g., syrinx in birds, vocal cords in humans) with specific sequences to
produce meaning (alarm calls, song, contact calls, etc.).
The acoustic codes are particularly complex in songbirds and relatively simple
in other birds and in frogs and fishes.
An acoustic code is composed of indivisible units that represent the alphabet in
the sonic language. Although the majority of the communicative processes is
devoted to intraspecific communication, several species have the capacity to under-
stand the sonic communication of other associated species. This ability creates a
favorable condition for the organization of interspecific indirect exchange of
information, often invoked as proof of the existence of a community level over
the population level.
Considering that every signal is species specific and that humans cannot under-
stand the meaning of animals signals and vice versa, indirect methods must be used
to explore this informative dimension.
For instance, when a signal is repeated under the same circumstances it is
reasonable to find a meaning correlated with that circumstance after a reasonable
accumulation of evidence. In this way we cannot determine the meaning of the
signal but can perceive its effects on the receiver. In particular, signals that vary
dichotomously are particularly adapted to study the semantics of these signals. In
particular, the study of the acoustic repertoire of those species whose song reper-
toire can be divided in distinct categories is useful. Thus, species of the wood
warbler genera Vermivora , Dendroica , Parula , Mniotilta , and Setophaga have a
song repertoire that can be divided into two distinct categories.
An important study was conducted by Byers ( 1996 ) that has selected categorical
variables for investigating the acoustic repertoire of the chestnut-sided warbler
( Dendroica pensylvanica ).
The following categorical variables were selected:
Stage of breeding
Song before male movement