The Ecology of Avian Acoustical Signals
97
how song contributes to the stability of the social relationships. As in the territory
defence hypothesis, effects of singing are immediate. So, for example, males
should sing when fertile females ready to engage in an extrapair copulation are
within earshot (Staicer et a!. 1996). In this view information translates into female
decisions without much delay. Hence, the timing and intensity of signaling must
match those of the actions of the receiver. I suggest that the main issue in social
dynamics is the singer's uncertainty about the status of the other members of the
social network. Singing then is as much information-gathering through provoking
the signals of others, as it constitutes valuable information for the receiver. Since
uncertainty is maximal after the night, this information is most valuable in the
morning, and it should influence all later decisions.
7 Concluding Remarks
Bird song is arguably the most intensively studied aspect of avian biology.
Nevertheless, bird calls and the songs of nonoscines remain little understood. Bird
songs are complex, carry many messages, have several functions, and are subject
to many different influences, none the least of which is the fact that they are
learned (Catchpole and Slater 1995). The acoustic communication of other birds,
such as woodpeckers and antbirds, may represent much better models for studying
general principles of communication. Since the auditory system codes natural
sounds at higher information rates and efficiencies than white noise (Rieke et a!.
1995) and transmission properties may also be sensitive to complex signal
features, especially in temporal dimensions, more experiments that involve
naturalistic sounds are needed.
We need measurements of real sender-receiver interactions under biologically
relevant conditions. They should cover more signal types and more species or
clades. The acoustical properties of many natural habitats are still unknown.
Clearly, more realistic models and empirical measurements of sound propagation
in forest canopies are urgently needed, particularly because much, if not most, of
avian acoustic signals in forests originate in this layer.
Much could certainly be gained if the requirements for information-gathering
were more respected. Most signalers also need to receive information and their
broadcasting may have the main purpose of eliciting information from others.
With the exception of song learning studies, practically all laboratory and field
experiments deal with immediate responses of birds to acoustic signals. To gain
more insights, we have to extend this approach and compare informed versus
uninformed receivers, not only at the time they become informed but also after
they have been informed. Very much along the same line, I would also argue for a
stronger emphasis on studying the need for information by the receiver, how that
influences the design and performance of its senses, the signaling behavior of
conspecifics and other organisms, and its own information-gathering efforts
through signaling. After all, information is the currency of communication.
97
how song contributes to the stability of the social relationships. As in the territory
defence hypothesis, effects of singing are immediate. So, for example, males
should sing when fertile females ready to engage in an extrapair copulation are
within earshot (Staicer et a!. 1996). In this view information translates into female
decisions without much delay. Hence, the timing and intensity of signaling must
match those of the actions of the receiver. I suggest that the main issue in social
dynamics is the singer's uncertainty about the status of the other members of the
social network. Singing then is as much information-gathering through provoking
the signals of others, as it constitutes valuable information for the receiver. Since
uncertainty is maximal after the night, this information is most valuable in the
morning, and it should influence all later decisions.
7 Concluding Remarks
Bird song is arguably the most intensively studied aspect of avian biology.
Nevertheless, bird calls and the songs of nonoscines remain little understood. Bird
songs are complex, carry many messages, have several functions, and are subject
to many different influences, none the least of which is the fact that they are
learned (Catchpole and Slater 1995). The acoustic communication of other birds,
such as woodpeckers and antbirds, may represent much better models for studying
general principles of communication. Since the auditory system codes natural
sounds at higher information rates and efficiencies than white noise (Rieke et a!.
1995) and transmission properties may also be sensitive to complex signal
features, especially in temporal dimensions, more experiments that involve
naturalistic sounds are needed.
We need measurements of real sender-receiver interactions under biologically
relevant conditions. They should cover more signal types and more species or
clades. The acoustical properties of many natural habitats are still unknown.
Clearly, more realistic models and empirical measurements of sound propagation
in forest canopies are urgently needed, particularly because much, if not most, of
avian acoustic signals in forests originate in this layer.
Much could certainly be gained if the requirements for information-gathering
were more respected. Most signalers also need to receive information and their
broadcasting may have the main purpose of eliciting information from others.
With the exception of song learning studies, practically all laboratory and field
experiments deal with immediate responses of birds to acoustic signals. To gain
more insights, we have to extend this approach and compare informed versus
uninformed receivers, not only at the time they become informed but also after
they have been informed. Very much along the same line, I would also argue for a
stronger emphasis on studying the need for information by the receiver, how that
influences the design and performance of its senses, the signaling behavior of
conspecifics and other organisms, and its own information-gathering efforts
through signaling. After all, information is the currency of communication.