Communication Theories - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 65

The success of a signal largely depends on the physiological status of the
receiver engaged in more strategic functions. In this case attentiveness to the signal
could be lower and the signal not considered. The receptiveness of the receiver may
be influenced by other conditions or concurrent functions. Thus, in time of scarcity
of foraging resources the priority is to find food and not to reply to a mating or
social signal. Species under predator or parasitoid pressure can evolve a compro-
mise. Aggregation can reinforce signals, as in frogs, but this could attract more
parasitoids than would isolated males.
A signal quality has two components: clarity and value (efficacy and strategy can
be used as synonyms). A signal component can be low in quality because is difficult
to receive and to process, or because it gives false or misleading information about
the emitter (strategy).
The quality of a signal assures that the receiver can decode the signals appropri-
ately, but a low-quality signal creates difficulties in discrimination. When a type of
signal such as the acoustic one is difficult to achieve, another type of signal, for
instance, a visual cue, can be utilized at integration to maintain an open communi-
cative channel between subjects.
Signal, sensory, and cognitive systems are the major components of the commu-
nicative system, and a change in one of these may have fitness consequences for the
other two. In particular, this aspect is very important in sexual selection.
For instance, males that emit more efficient signals to attract females will have
an evident chance to perpetuate their lineages. This attitude is known as “sensory
exploitation,” that is, the capacity of a male to manipulate the sensory reception of
the females.
In conclusion, the evolution of the sensory system will favor the signals that are
easy to receive, to distinguish, and easiest for basing decisions, and the sensory
system, signals, and signaling behavior thus evolve contemporarily.
Species living in the same environmental condition can evolve similar signals as
expression of convergent evolution of some plastic traits. We can call this process a
“sensory drive,” which means that different species under the same environmental
conditions evolve similar signals that can be predicted starting from predictable
conditions.
Territorial birds use sound with a multitude of functions, but territorial defense
seems one of the most common strategies in this group. In Fig. 4.1 are represented
different hypothetical combinations of spatial dislocation of two concurrent males as a
theoretical example of the complexity of communication mechanisms (Naguib 2005 ).
4.3 Eavesdropping and Interspecific Communication
Eavesdropping is a way in which an individual voluntarily or involuntarily
intercepts a communication broadcast for another individual. Peake ( 2005 ) reports
“In the context of animal communication, the term has been used in a number of
different ways that can be summed up by a general definition: the use of information
in signals by individuals other than the primary target.”