Bottlenose dolphins hunt prey using their keen eyesight, hearing and a sonar system known as echolocation. But now, researchers have discovered the marine mammals may be aided by another sense: electric pulse detection.
In a new study published Thursday in the Journal of Experimental Biology, scientists report that bottlenose dolphins have dimples called vibrissal pits on their beaks that perceive electricity—and may help them gobble up fish and navigate around the ocean. Newborn dolphins have whiskers in these pits that fall out soon after birth, so researchers previously thought they were nonfunctional.
The finding suggests bottlenose dolphins may join a small group of mammals with the rare capacity for electroreception: Aside from dolphins, only platypuses and echidnas seem to possess this unusual sense. However, sharks and other elasmobranchs—a group of cartilaginous fish including rays, skates and sawfish—are very sensitive to electric fields. Some sharks can detect weak currents as low as five billionths of a volt per square centimeter.
To test this ability in the marine mammals, researchers worked with trainers to teach two captive bottlenose dolphins, named Dolly and Donna, to rest their jaws on a metal bar in their tank and swim away when they sensed an electrical impulse. The researchers then delivered fields of varying strengths, using electrodes connected to a custom-built electric field generator.
“It’s basically the same as when we go to the doctor’s and do a hearing test—we have to press a button as soon as we hear a sound,” lead author Tim Hüttner, a biologist at the Nuremberg Zoo in Germany, tells Carolyn Wilke of the New York Times. “The dolphins responded correctly on the first trial.”
Donna showed a higher sensitivity—she was able to detect direct currents (DC) as low as 2.4 microvolts per centimeter, while Dolly’s threshold was 5.5 microvolts per centimeter.
After delivering direct currents, the researchers tested the dolphins’ ability to perceive alternating current (AC) electric fields. All organisms underwater produce static direct current fields, but some, such as fish, also produce pulsing AC fields as they move their gills, per a statement from The Company of Biologists.
The team tested AC fields of varying frequencies—pulsing either once, five times or 25 times per second. They found that both dolphins responded well to low-frequency AC electric fields, although they appeared more sensitive to DC fields.
“The sensitivity to weak electric fields helps a dolphin search for fish hidden in sediment over the last few centimeters before snapping them up,” Guido Dehnhardt, a marine biologist from the University of Rostock in Germany, says in the statement.
But other researchers caution that the study only included two individuals, and both were captive: “We do not know whether this ability is actually used in the wild,” Juliana López-Marulanda, a marine biologist at University Paris Nanterre in France who was not involved with the study, tells the Times.
Beyond hunting down prey, electroreception may help dolphins navigate by feeling changes in the Earth’s magnetic field, per the paper. Next, the research team wants to study this sense as dolphins move.
Additionally, previous research had suggested a link between solar storms, which can cause shifts in the planet’s magnetic field, and mass strandings of dolphins and whales. The new study might begin to explain why that is, Dehnhardt tells the Times.
“There’s just so much to find out,” Paul Nachtigall, a marine biologist at the University of Hawaii at Manoa who did not participate in the research, tells Science News’ Saima S. Iqbal. “This study is just the first page of a book.”