Sunday, September 29, 2013

The Victory Squawk of the Little Blue Penguin

Apr. 03, 2012
by Kara Rogers
Little Penguin (Eudyptula minor) family exiting burrow, Bruny Island, Tasmania, Australia. Photo by Noodle snacks.

Victory is sweet, so much so that we often feel compelled to rejoice with a cry of triumph. For some animals, that cry not only announces a win to all those within earshot but also serves surprisingly complex social functions. Take, for instance, the call of the victorious little blue penguin (Eudyptula minor), which a recent study in the journal Animal Behavior revealed has a direct effect on the behavior of “social eavesdroppers” -- penguins who, from the safety of their burrows, assess the quality of fighting individuals based solely on their vocalizations.

Male little blue penguins are fierce defenders of their territories and frequently become engaged in flipper-slapping territorial disputes. At the conclusion of a scuffle, the winner celebrates with a so-called triumph display, in which he delivers a victory bray -- a distinctive squawk that according to the new study serves as a sort of warning signal to other males in the colony, potentially mitigating future confrontations for the winner and preventing embarrassing defeats for lesser male challengers.
Little blue penguins, which are the smallest penguins in the world, are social animals that use vocalization during activities such as courtship and foraging and as a way of announcing their arrival at their home burrows. However, while much is known about the various functions of many of the penguins' calls, the social significance of vocalization associated with victory calls had remained unclear.

To assess the impact of triumph brays on the behavior of eavesdropping penguins, the scientists played a recording of a vocal exchange and flipper-slapping fight between territorial males and then played recordings of both the victor's triumph call and the loser's call. They then measured the heart rates of eavesdroppers in response to the sounds using heart monitors hidden in artificial eggs that were placed in the penguins' nests. The team found that eavesdropping males' heart rates increased in response to the victor's call when compared with the loser's call. In addition, in simulated approach experiments in which the loser's or winner's call was played just outside the entrance of an eavesdropper's burrow, the scientists discovered that eavesdropping males challenged the loser's call with vocalizations of their own but fell silent when the triumph call was played.

Triumph displays and other forms of postconflict signaling have been documented in a variety of species, including birds such as the Canada goose (Branta canadensis), the greylag goose (Anser anser), and the bell shrike (Laniarius aethiopicus), as well as animals such as the green frog (Rana clamitans) and an insect known as the Wellington tree weta (Hemideina crassidens). Postconflict signaling in these species appears to function either as a form of advertising, in which the winner's display communicates his dominance to eavesdroppers, or as a form of intimidation, in which the winner's display serves to reduce the chance that the loser will initiate a future challenge. Thus, in many ways, by showing off a little after a victory, these animals are simply establishing their reputation as winners. In other words, they're behaving very much like humans.


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