Animal Behaviour: A Very Short Introduction by Tristram D. Wyatt

Author:Tristram D. Wyatt
Language: eng
Format: azw3, epub
Tags: Zoology, Science, Life Sciences, Biology, General
ISBN: 9780191020957
Publisher: Oxford University Press
Published: 2017-02-10T18:38:12.144502+00:00

Honest signals

Across the animal kingdom, signals within a species seem to be honest on the whole. This might seem surprising: what is to stop animals from boasting or deceiving when they communicate? One reason is that, on average, signals must communicate useful or truthful information to ensure that the receiver does not evolve to ignore the signal—like the villagers in Aesop’s story of the boy who cried ‘wolf’.

A variety of additional mechanisms seem to ensure that most signals are honest. The first mechanism applies to signals which reflect an inherent feature (index) of the signaller, which cannot be faked. In the spring, European common toads (Bufo bufo) gather in ponds to spawn. Males pair with females by gripping their backs. Unpaired males try to dislodge the males in such pairs so they can take their place. When a paired male is challenged by another male attempting to push him off the female, the paired male croaks. His croak gives a reliable signal of his size: larger males have longer vocal chords that produce a deeper pitched croak. To test this, researchers temporarily silenced some paired males by placing a rubber band over their mouths. Then, while a medium sized male attempted to dislodge him from the female, the researchers played back the sound of either a deep or high pitched croak next to the silenced male (Figure 15). Whether the size of the silenced paired male was large or small, fewer attempts were made if the deep croak was played. It seems that the rival males are using the croak as a signal to assess the likelihood of success: a large male with a deep croak will be harder to dislodge.

15. Male toads are more likely to attempt to dislodge a male, large or small, on top of a female if they hear a recording of the croak of a small male.

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