"Open Mouth"

Why do dolphins smile? New findings are surprising

(Bild: dapd)

Dolphins give the impression that they are always smiling - in fact, very little can be read from their facial expressions. But there is at least one clear signal ...

The friendly facial expression of dolphins is an innate anatomical characteristic: it basically says nothing about the animal's emotional state. They still seem to smile even when they are badly stressed or in severe pain.

However, according to a study, the marine mammals like to open their mouths when playing - which looks as if they are openly smiling at their counterpart. The expression is mainly used when the respective playmate can see it, the research team reports in the journal "iScience".

The scientists led by Elisabetta Palagi from the University of Pisa have now observed bottlenose dolphins (Tursiops truncatus), which really enjoy playing. They filmed and analyzed how captive animals played with each other, alone or with their trainers.

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(Bild: APA/AFP/Christophe SIMON)

Can mirror conspecifics
The bottlenose dolphins mainly show an expression called "open mouth" during social play with other dolphins or - more rarely - humans, almost never during individual play. If the playmate could see the open mouth, it often opened its mouth as well - which gives the impression to humans that the animals are laughing happily at each other. The results showed that the open-mouth expression also occurs in dolphins and that bottlenose dolphins are probably able to mirror the behavior of conspecifics, according to the researchers.

Many animals like to play extensively, especially during their childhood. In doing so, the movement sequences required for hunting or fighting with conspecifics, for example, are trained later on. Social interactions and hierarchies are learned, and courtship and mating behavior can also be tested through play.

In some animal groups, such as wolves, primates and dolphins, adult group members also often play. Communication is of central importance here: after all, the behaviors and facial expressions used sometimes have patterns typical of aggression - friendly play can unintentionally degenerate into a real fight.

One example of such communication is the open-mouth expression, which is probably derived from biting: a wide-open mouth, but where the teeth are not shown threateningly and the overall facial expression remains relaxed. It signals to the other person that all wrangling and anger is to be understood as fun. The expression can also be seen in humans, the researchers explain: when laughing.

A lifetime offun
Bottlenose dolphins are also a lifetime of fun. They use natural waves for "surfing" or swim in front of ships in their bow wave, jump several meters high out of the water and hit the water surface with their tail fin. Seaweed, corals and other marine animals are also popular play objects. The dolphins also create air bubbles under water, which they play with. They prefer to do all this together with others rather than alone.