Sonic Patterns II: The Animal Choruses - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 198

happen, and females must select not just the more energetic male but they must
decide between calls of lower frequency and call rate. In natural conditions, females
must decide in acoustically unfavorable conditions, and they must make the best
choice under these real conditions.
Females seem able to eavesdrop on interacting males and to extract the best
information on the quality of males. Most of the selections are for leading calls,
although in some cases the follower call is preferred.
A simplified model in which a female approaches the first male that it encounters
is counterbalanced by evidence that females monitor the different calls of more
males.
The eavesdropping strategy seems to be utilized also by silent males that
intercept females after other males have intensified their calling for the presence
of a female.
So, in conclusion silent males monitor the situation of other males and then
decide to enter into the mating arena, privatizing with an ad hoc call, as in
Eleutherodactylus coqui.
Choruses in frogs are the result of contemporary behavior of a signaler and a
receiver, and in addition to the function of sexual selection choruses in frogs also
act as a beacon that allows frogs to locate the breeding pond precisely.
The wood frog ( Rana sylvatica ) distributed across North America is an explo-
sive breeding amphibian. Timing and location vary according to the local climatic
factors (rainfall and change in temperature). Bee ( 2007 ) has conducted experiments
on males of this frog demonstrating that the phonotaxis expressed by wood frog
males is not only connected with the sexual mechanism to attract females but is also
a useful tool (sonic eco-field) or beacon to intercept accurately and in a short time
the breeding assemblage, which occurs only in favorable conditions and for a very
restricted time period.
7.5 Choruses in Birds
In birds, physiological requirements and behavioral traits are the two major proxies
at the basis of the chorus pattern. We call the first point simply an energetic
hypothesis, and the second a behavioral hypothesis that must be added to and
integrated with the hypotheses discussed in Sect. 7.2 .
7.5.1 The Energetic Hypothesis
The energetic hypothesis states that the amount of fat reserves accumulated in the
previous day is responsible for the quantity and loudness of the song broadcast by
an individual at dawn or at dusk.