African
penguin getting ready to dive -
© eSDeO / Pixabay
Microphones were attached to the backs of penguins to check if they emitted - or not - vocalizations while diving, according to a study published by our partner The Conversation.
Other marine predators, such as dolphins, sea lions and sea turtles are known to vocalize underwater.
The analysis of this phenomenon was carried out by Andréa Thiebault, postdoctoral fellow and Pierre Pistorius, teacher (both at Nelson Mandela University [South Africa]), Isabelle Charrier, CNRS researcher in bioacoustics and Thierry Aubin, master of research at CNRS (both at Paris-Saclay University).
Like all seabirds, penguins are very talkative on land when they come to breed.
They use vocalizations to recognize each other between partners and between parents and chicks.
Outside of the breeding season, seabirds spend most of their life at sea and are adapted to the marine environment in which they feed.
Penguins are also unique for their exceptional diving abilities.
They use their modified wings to propel themselves underwater and dive up to 30 to 500 meters depending on the species, in search of prey.
We investigated whether penguins were able to make sounds underwater.
For this, our Marine Predator Research Unit (MAPRU) at Nelson Mandela University (South Africa) attached miniaturized cameras with built-in microphones to the backs of three penguin species: the King penguin, the gentoo penguin and the macaroni penguin.
Our study presents the first evidence that penguins make sounds underwater when hunting.
King penguins at sea © John Dickens (via The Conversation)
Save the penguins at sea
Due to recording difficulties, the vocalizations of penguins at sea are still very little known.
Thanks to recent technological advances and the miniaturization of cameras in particular, such observations are becoming possible.
We recorded a total of 203 underwater vocalizations in the three penguin species studied, during almost 5 hours of underwater recording (representing 93 dives).
These three species were chosen because they reflect the diversity of the feeding strategies of penguins at sea. The king penguin feeds mainly on fish caught at great depth (200 meters), while the macaroni penguin feeds on krill in the ten first meters of the water column.
The gentoo penguin, meanwhile, is very generalist, being able to feed on a wide variety of prey and at all depths.
Gentoo penguin turning over the egg it incubates (Neko Harbor, Antarctic Peninsula - December 2016) © Kounilig / Wikimedia CC BY-SA 4.0
The penguins were captured in their breeding colonies on Marion Island in sub-Antarctica at the time of their departure to sea. The cameras were recovered when the individuals returned to the colony after a sea voyage.
Our results show that all underwater vocalizations were emitted during feeding dives.
Most of them (73%) were emitted during the bottom phase of the dives, which corresponds to the food intake phase (as opposed to the descent and ascent phases).
Here is a video clip showing a king penguin dive, as recorded with the on-board camera:
The majority of vocalizations were directly associated with prey capture behavior: emitted just after acceleration (prey pursuit) or emitted just before an attempted capture.
These underwater vocalizations were recorded in the three penguin species studied.
This suggests that such vocal behavior could exist in other species.
However, the fact that we observed vocalizations in greater proportion when penguins fed on fish, and not on krill or molluscs, one would think that this behavior could be more common in penguins which feed on fish.
Unexpected ?
Until now, the existence of underwater vocalizations in penguins was completely unknown, although some experts on our bioacoustics team suspected their existence.
We already knew that the vocalizations emitted on the surface by gentoo penguins were associated with the grouping of individuals.
African penguins are also known to vocalize on the surface, mainly during the prey search phases (potentially to communicate between congeners) and when hunting in groups on schools of fish (potentially to synchronize their hunting behaviors).
Other marine predators, such as dolphins, sea lions and sea turtles are known to vocalize underwater.
Why not the penguins?
Our “Oceans” file
A multitude of unanswered questions ...
Now that we know that penguins vocalize underwater, new questions arise.
For example, how are penguins able to make sounds underwater, given the pressure at depth?
Why do penguins vocalize underwater?
Are the different vocalizations that we recorded used to exchange the same information?
Do penguins produce sounds in different contexts?
Are these vocalizations simply a reflection of physiological needs due to freediving, to adjust buoyancy for example?
Can they play a role in social interactions?
Can they be part of a hunting technique and be used to immobilize prey?
Future research will, we hope, provide answers to these questions in order to better understand the fascinating behaviors of penguins at sea.
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This analysis was written (in English) by Andréa Thiebault, postdoctoral fellow and Pierre Pistorius, teacher (both at Nelson Mandela University [South Af.]), Isabelle Charrier, CNRS researcher in bioacoustics and Thierry Aubin, master of research at CNRS (both at Paris-Saclay University).
The original article was translated by and then published on The Conversation website.
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