Sonic Patterns II: The Animal Choruses - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 203

Intrinsic factors, environmental factors, and social factors can concur in the
chorus performance.
Among the several hypotheses to explain this phenomenon, the acoustic trans-
mission hypothesis has received much credit. This hypothesis claims a more
favorable condition of acoustic transmission at dawn and at dusk for a quieter
atmosphere and the lowest background noise. Reduced foraging efficiency at dawn
and at dusk and an excess of food storage the day before are further good
arguments.
In birds, there is evidence that choruses can be explained by at least two major
hypotheses: an energetic hypothesis and a behavioral hypothesis. According to the
first hypothesis, the choruses are performed in coincidence with a food surplus or
fat reserves. The second hypothesis considers the choruses as an interactive com-
munication between concurrent males and seems a reaction of the past day's vocal
interactions between males.
In amphibians choruses are very common, energetically costly, and occur
especially during the short reproductive period. The acoustic interference seems
quite high, but analysis at a fine temporal scale demonstrated in many cases how
males have the capacity to collate the calls in acoustic gaps, reducing the apparent
overlap.
A cooperative hypothesis according to which a chorus produce benefits in the
entire population is opposed to a competitive hypothesis in which a leading caller is
preferred in sexual selection. In fact, it has been demonstrated that females are
attracted by leading and loud signals.
A further function of amphibian choruses is discussed in terms of an acoustic
beacon for individuals to find the adopted pond in a short time, considering the
ephemeral condition of many vernal ponds.
Songs during choruses have in many cases a reproductive function and sexual
selection. Individual singing early, louder, and longer receives the advantage of the
best mating process with more healthy females. The high singing activity at chorus
is for some species a strategy to defend their territory, and in others to assure a
extra-copulatory opportunity or nesting replacement after failure caused by nest
predation or female desertion.
References
Amrhein V, Erne N (2006) Dawn singing reflects past territorial challenges in the winter wren.
Anim Behav 71:1075-1080
Barnett CA, Briskie JW (2007) Energetic state and performance of dawn chorus in silvereyes
( Zosterops lateralis ). Behav Ecol Sociobiol 61:579-587
Bee MA (2007) Selective phonotaxis by male wood frogs ( Rana sylvatica ) to the sound of a
chorus. Behav Ecol Sociobiol 61:955-966
Brown TJ, Handford P (2003) Why birds sing at dawn: the role of consistent song transmission.
Ibis 145:120-129