Penguins making quick, high-pitched sounds underwater while hunting have been recorded for the first time in what researchers say may indicate the stealthy birds communicate with one another while searching for food. It's known that other air-breathing marine predators like whales and dolphins make vocalizations underwater, but until now it had never been recorded in sea birds.
Penguins are known to be highly vocal on land and use communication as a crucial role in reproduction. The tuxedo-clad birds emit vocalizations from the sea surface when they commute to and from their hunting grounds, which may help them to form groups at sea, as well as employ vocal recognition to find their breeding colonies, partner, nest, and offspring when back on land. However, the birds spend most of their time at sea having lost their ability to fly long ago, replacing it with a suite of adaptations to hunt below the ocean waves at extreme depths of up to 500 meters (~1,600 feet) in search of prey. The new research published in the journal Zoological Science suggests that penguins may also communicate vocally underwater while hunting at sea.
Working on Marion Island off the coast of South Africa, a team of researchers equipped three different species of foraging adult penguins with video cameras that had built-in microphones. Each of the penguin species was unique in their hunting methodologies and preferred prey. King penguins (Aptenodytes patagonicus) dive between 100 and 250 meters (330 to 820 feet) in search of fish while macaroni penguins (Eudyptes chrysolophus) forage within the top 100 meters of the water column looking mainly for crustaceans. On the other hand, gentoo penguins (Pygoscelis papua) tend to eat a little bit of everything across the water column.
Each of the species studied made sounds when hunting for food but vocalized underwater in various feeding contexts. In all, more than 200 underwater vocalizations were recorded over almost five hours of underwater footage. Most were very short in duration – just a half-second on average – with amplitude between 680 and 1097 Hz, depending on the species. All vocalizations were emitted during feeding dives, more than half of which were directly associated with hunting behavior.
“This suggests that such underwater vocal behavior may exist in all penguin species. However, underwater vocalizations were recorded in much higher proportion when penguins were feeding on fish, compared to crustaceans or cephalopods,” write the authors.
Earlier this month, another study documented African penguins in captivity using the same speech patterns as humans, in the form of often-used “words” and longer vocalizations for more complex messages. The researchers note that communicating underwater may additionally enhance the birds’ ability to hunt, however, the findings arguably present more questions than they do answers. For starters, how are the penguins able to produce sound at such a highly pressurized depth? Are the sounds emitted intentionally or are they instead a byproduct of holding their breath? Although the vocalizations appear to be related to the hunting behavior, the authors add that the function of the vocalizations remains speculative and warrant further investigation.
“As intriguing as these observations are, we failed to demonstrate the adaptive significance of this behavior, although it seems likely to enhance foraging success,” wrote the researchers. “We strongly encourage further research on this intriguing behavioral phenomenon, which contributes to the debates on the uses of underwater vocalizations by diving predators.