Biology Reference
In-Depth Information
at dawn, which represents an advantage. The variability of the transmission quality
increased with the distance at which the signals were re-recorded.
As every hypothesis, the acoustic transmission hypothesis remains quite contro-
versial, as argued by Dabelsteen and Mathevon ( 2002 ) after conducting
experiments on the propagation of two types of songs of the blackcap ( Sylvia
atricapilla ), a small warbler very common across the shrubland and forest habitats
of Europe. They carried out experiments in a broadleaf forest, recording the sounds
at dawn, in midmorning, and early in the afternoon, without finding environmental
conditions more favorable to acoustic propagation than those at dawn, rejecting this
hypothesis.
It has been observed in a Mediterranean scrubland that background noise
increases outside the breeding season (Farina et al. 2013 ) and that the period
from March to September has a significant higher SNR, although some temporal
peaks of noisy sources have been observed, especially during the second part of
the day.
Among other possible explanations of the chorus phenomenon, at least two have
received credit:
The first stated that foraging is inefficient in poor light at dawn (Kacelnik's
explanation; Kacelnik 1979 ) and that the dawn time is reserved for social
communication.
The second explanation argues that stochasticity in foraging success and overnight
energy requirement allow an energetic surplus (Hutchinson 2002 ).
Considering the great number of hypotheses advanced by many authors (e.g.,
Burt and Vehrencamp 2005 ), it is reasonable to admit that social hypotheses are not
mutually exclusive and that males can use this strategy to increase social
interactions. The dawn chorus seems to create a communication network where
there are at least three individuals in continuous contact with each other. Three
types of communication network can be described:
A broadcasting network in which one individual sends the vocal communication to
two or more receivers.
An eavesdropping network where two senders interact and two or more receivers
eavesdrop to obtain information from the two interacting subjects.
Finally, an interactive network where all the individuals are sending information
and in turn they eavesdrop the others (Fig. 7.3 ). This system in the real world
seems a little more complex, where probably there are non-interacting females
and floater males that are eavesdropping.
However, to find male-to-male interactions is not an easy task at dawn when
many individuals are singing simultaneously and where is extremely difficult to
distinguish foreground from background threshold.
Henwood and Fabrick ( 1979 ) have processed a quantitative analysis of the dawn
chorus according to the time of the day. They arranged a mathematical model to test
the various attenuation mechanisms in action under different micrometereological
conditions in different habitats.
Search WWH ::




Custom Search