The Firth of Clyde is a vast saltwater strait on Scotland’s west coast that is home to hundreds of harbor porpoises and one dolphin named Kylie.
Kylie hasn’t been seen with any other common dolphins (Delphinus delphis) in at least 14 years, yet she’s not alone. Visitors to the marina on clear days in the Clyde might often observe Kylie swimming alongside harbor porpoises (Phocoena phocoena), her cetacean cousins about two-thirds her size.
According to new research published in Bioacoustics in January, Kylie’s ties to porpoises are closer than scientists thought. Kylie does not whistle, despite the fact that a common dolphin’s vocal repertoire should comprise a variety of clicks, whistles, and pulse cries. She “talks” more like a harbor porpoise, which communicates with high-pitched bursts of clicks.
According to the research, she may be conversing with the porpoises, or at least attempting to. It’s part of a growing corpus of work that reveals a fascinating world of relationships between various cetacean species.
“Clearly, species in the wild interact far more than we imagined,” says Denise Herzing, a dolphin behavior expert.
A wild dolphin named Kylie may be able to “converse” with porpoises, a striking example of cross-species communication.
dolphin behavior expert Denise Herzing.
The porpoise code
Years ago, the Clyde’s lone dolphin resident was fond of a buoy at the mouth of a loch known as the Kyles of Bute, so residents dubbed her Kylie. However, no one knows where she came from or why dolphins end up alone, according to David Nairn, founder and director of Clyde Porpoise, a local group dedicated to investigating and safeguarding marine mammals. Kylie hasn’t been seen in a year, but locals are hoping she’ll show up soon.
Some solitary dolphins become separated from their original groups due to storms or human activities, or they are orphaned. Others, according to a 2019 study on solitary dolphins globally, may just be less gregarious and prefer their privacy.
Nairn borrowed a hydrophone and trailed it behind his sailing yacht, the Saorsa, to discover more about Kylie’s interaction with the porpoises. From 2016 to 2018, Nairn recorded audio of many encounters between Kylie and porpoises.
She “clearly identifies as a porpoise,” says Nairn, a college-trained marine biologist.
Mel Cosentino, a Ph.D. student at the University of Strathclyde in Glasgow at the time, sifted through thousands of ultrasonic cetacean clicks from the recordings.
While dolphins almost always whistle, porpoises never do. Instead, they use narrow-band, high-frequency (NBHF) clicks with eight to fifteen amplitude peaks at roughly 130 kilobits per second to communicate.
“You have to play it about a hundred times slower to hear an NBHF click,” Cosentino says. (Pitch falls when sounds are slowed down. Humans can hear between 20 hertz and 20 kilohertz (about the lowest pedal on a pipe organ).
Cosentino discovered lower-frequency clicks typical of common dolphins in the recordings. Even when Kylie looked to be alone, Cosentino discovered clicks with eight or more amplitude peaks at the critical 130 kilohertz frequency—the frequency at which porpoises communicate. In other words, even when she’s alone, Kylie speaks like a dolphin. Kyle, unlike other dolphins, never whistles, according to the researchers.
Cosentino observed that the exchanges between Kylie and the porpoises followed the rhythm of a “conversation” between members of the same species—turn-taking with little overlap—though it’s unclear how much useful information is communicated in Kylie’s efforts at porpoise clicking.
“It may be me barking at my dog and him barking back,” Cosentino speculates.
Regardless, this action reflects “an attempt” at communication that the “porpoises definitely recognize,” according to Herzing, research director of the Wild Dolphin Project, who has studied the behavior of Atlantic spotted dolphins in the Bahamas for more than three decades. Herzing, who was not involved in the study, commends the authors for the ingenious experimental design in a natural context.
“The results are tantalizing,” she says. “What’s very telling is that Kylie doesn’t produce any whistles, because dolphins always make whistles and porpoises never do.”
One of the most difficult aspects of marine bioacoustics, according to Laela Sayigh, an associate professor of animal behavior at Hampshire College, is determining which organisms create which sounds. “They don’t make any exterior movement linked with sound, and you can’t see them most of the time,” Sayigh explains.
In this situation, Kylie can be differentiated by her accent. “It still seems like she’s straining” to get as high-pitched as the porpoises, Cosentino adds, noting that the peaks on her clicks aren’t as crisp as they should be and that there are some lower-frequency sounds mixed in with the high notes.
“Kylie would be Pavarotti and the porpoises would be Mariah Carey if they were singers.”
Cetaceans in captivity are capable of vocal mimics, according to Herzing, who cites killer whales and belugas that mimic bottlenose dolphin tankmates. A 2016 bioacoustics study discovered that a cross-fostered Risso’s dolphin in an Italian marine park whistled more like the bottlenose dolphins it was nurtured with than wild individuals of its species.
However, the fact that Kylie emits NBHF-like clicks while alone “raises the question” of whether she’s clicking to communicate with harbor porpoises or just duplicating the sound, according to Sayigh.
Conversation with a Melonhead
Cetaceans, which include dolphins, porpoises, and whales, are descendants of land-dwelling mammals that found their way back to the ocean over millions of years. “Evolutionarily, the nostrils became the blowhole,” Cosentino explains, as they readapted to life in the ocean.
While toothed whales, such as dolphins and porpoises, only have one open nostril, both nasal chambers are present beneath the surface, each capped by a muscular structure known as “monkey lips.” (Cetacean anatomy is frequently described in vivid words, derived from whalers’ reports.) Monkey lips are similar to our own vocal cords in that they govern airflow—and when air is driven from the lungs through the “lips” on the left nasal cavity, it’s “like letting the air out of a balloon,” producing warbling whistles. Cosentino says.
The clicks utilized in communication and navigation are produced by the right nasal cavity. It comes to a halt near a melon, a fatty deposit on the toothed whale’s forehead that intensifies and focuses the cetacean’s vocalizations. Because both sets of monkey lips function independently, some cetaceans, such as bottlenose dolphins, can click and whistle at the same time, akin to Mongolian throat-singing.
Kylie’s story is part of a larger study of how cetaceans interact with members of other species. “They’re tremendously gregarious, very sexual, and very communicative,” Herzing explains. “Sound is a natural means for these animals to live and adapt socially.”
Interspecies adoptions that have been well-documented also show that species divisions may not be as clear-cut as previously imagined. Two examples are a Canadian beluga pod that took in a narwhal calf and a spinner dolphin that lived with Tahiti bottlenose for 20 years.
Recent DNA tests also show that we’ve merely touched the surface of hybridization, says Herzing. Bottlenose dolphins have mated with at least ten different species both in captivity and in the wild, including cetaceans as diverse as the pilot whale and the Guiana dolphin. Researchers assume that cetaceans can hybridize so well due to their similar DNA—their species separated barely 10 million years ago.
Aside from her attempts at communication, Kylie appears to be similar to a porpoise in other respects. Nairn has witnessed female porpoises bring their young calves to engage with Kylie on several occasions. Nairn was startled to see porpoise calves swimming with the dolphin in echelon, a position right behind her pectoral fin that researchers suggest is the cetacean equivalent of “carrying” a baby, Nairn said.
According to Nairn, male porpoises have also been seen attempting to mount Kylie. But does she give up to their advances? “I’d even say she courts, aye,” Nairn confesses, chuckling. According to Herzing, mating is theoretically anatomically conceivable, but there haven’t been any scientifically recorded dolphin-porpoise hybrids.
Kylie has been missing since a week of heavy storms in February 2021 led a big drilling ship to become unmoored near her favorite buoy. Nairn said it’s not unusual for her to migrate after a major disruption to one of her “vacation buoys” somewhere in the Clyde for months, if not a year, but he can’t help but be concerned.
Nairn and his colleagues are excited to look for and listen to Kylie as soon as the spring field season begins, to discover what else she can teach us.
