I have been a sports-fan all my life. One of my biggest passions is tennis. As a child I played tennis in a small tennis club in Germany. When I think back to this time, many special “tennis sounds” come to my mind.
Tennis is a very auditory sport. Close your eyes and try to follow a game just with your ears. The sounds produced by the players tell you much about their emotions. Frustrated cursing is as omnipresent as cries of joy (see this video for a catalogue of typical behaviours and sounds). But even less obvious clues can help you to follow the game and hear which player is winning. Researchers from the University of Sussex showed that trained listeners could identify if a player is winning or losing by slight differences in the tone pitches.
A little penguin in its burrow. Image from Francesco Veronesi (CC BY-SA 2.0).
But why are players producing sounds anyway? One reason is that sounds and other nonverbal communication influence the confidence of the opponent. German researchers found that the confidence of basketball players in winning a game is influenced by the behaviour of their opponents.
A behaviour common in sports is the loud and obvious celebration. Behavioural ecologists call this type of behaviour a “triumph display” and it can be found in many animal species. Although human traits should usually not be attributed to animals, we might find parallels in the behaviour of humans and certain animal species in their triumph displays.
One species that performs a triumph display is the little penguin Eudyptula minor. In 2012, Lincoln researcher Laura E. Molles, along with Solveig C. Mouterde, Joseph R. Waas (both University of Waikato, Hamilton), David M. Duganzich (AgResearch Ltd, Ruakura Research Centre, Hamilton), Shireen Helps and Francis Helps (both Pohatu Penguins, Akaroa), investigated the influence of triumph display in little penguins on eavesdropping conspecifics.
Typical triumph display in Homo sapiens. Image from John W. Nguyen (CC BY 2.0).
Who does it better? Typical triumph display of a little penguin Eudyptula minor. Image provided by Joseph R. Waas.
The little penguin is the smallest penguin species and is native to New Zealand and Australia. There is a large colony close to Lincoln at Flea Bay (Banks Peninsula), where this study took place. Little penguins live in colonies and defend their territories, which leads to fights between individuals. After winning such a fight, little penguins perform a triumph display, which means they are basically bragging about their win.
This bragging includes a special winner call (there is also a loser call). Other penguins hearing this special call know exactly who won the fight, because they can recognise other penguins by their voice (you can find the amazing sound repertoire of little penguins right here).
3 little penguins in front of a burrow. Image from JJ Harrison (CC BY-SA 2.0).
To test the effect of this triumph display on eavesdropping penguins, the researchers had to develop a method to measure penguin reactions to these calls. They used playback recordings of triumph calls as well as loser calls and played them to individuals (males and females), which were breeding in artificial nest boxes. They played the calls from different distances, so that the penguin assumed that a winner or loser was approaching its box.
The reaction was recorded in two different ways. First, the vocal reaction was documented. Second, the change in heart rate was recorded. To obtain this measurement the researchers used a little trick. Before playing the sound sequence, they exchanged the eggs of the breeding penguin with an artificial egg (no worries – they took care of the real eggs and put them in the incubator for the duration of the experiment). This artificial egg was able to measure the heart rate when it was in contact with the skin of the breeding penguin (amazing technology!). After the experiment they switched the artificial egg back for the real eggs. The experiment did not lead to a higher rate of unsuccessful broods in the colony.
Little penguin in a nest box. Image from Andrea Schaffer (CC BY 2.0).
The calls mainly had an effect on males. Their heart rate increased after listening to winner calls, whereas it remained stable, when hearing loser calls. Males also responded more often than females. Males were more likely to react vocally to losers than to winners.
But what does this all mean? It seems that the triumph display in some ways influences the behaviour of eavesdropping penguins. Eavesdroppers clearly change their reaction towards individuals. If penguins think a winner is approaching their nest, they are more stressed and mostly remain silent. They are not stressed when an apparent loser approaches them, they vocally threaten the loser.
This is similar behaviour to what is expected from tennis players: they would choose to face a weaker player rather than challenging the proven winner. This behaviour seems advantageous for both sides. The triumphant winner of a fight, who lets everybody know that they won, is building a winning reputation. Consequently, the winner may not have to fight that often in the future. The eavesdropper also gains advantages from knowing the results of former fights. When another penguin approaches its burrow or nest box, it can decide to actively threaten the approaching penguin or just remain silent and not give his position away.
I was surprised that this phenomenon is still relatively poorly studied (this includes the time since this study). I found just a few other studies investigating triumph display and/or eavesdropping. And there are so many potential study species! I would suggest tennis players…
This blog article is based on the following peer-reviewed article:
The author Jonas Wobker is a postgraduate student in the Master of International Nature Conservation taught jointly at Lincoln University and University of Göttingen. He wrote this article as part of his assessment for ECOL 608 Research Methods in Ecology.