Dolphins have until now been known to use their blowholes to breathe and the new discovery highlights the animal's ability to adapt.
"We describe unusual respiration behavior in an adult New Zealand Dolphin (Cephalorhynchus hectori, also known as Hector's dolphin), which appeared to breathe, at least partially, via its mouth," the researchers wrote in a paper published in the journal Marine Mammal Science.
"We are not aware of any published sources describing this behaviour in cetaceans," the researchers noted.
Steve Dawson at the University of Otago in Dunedin, and his colleagues were studying the endangered species as part of a long-term conservation project when they noticed unusual behaviour in one member of a group of seven, the New Scientist reported.
Each time the dolphin surfaced, it approached at a steep angle and lifted its head higher out of the water than normal. The blowhole stayed shut while its mouth opened wide and made a sound consistent with sucking in air.
"In every surfacing we observed, the dolphin approached the surface at a steep angle, with its head emerging higher than normal from the water surface," the study said.
"Video and photographs of 38 surfacing sequences show that this individual dolphin did not breathe normally, via its blowhole, but appeared to be breathing mostly via its mouth," the researchers noted in the paper.
The animal probably learned to do this after its blowhole became blocked by a foreign object or injury, or because the muscles around it did not work properly, Dawson said.
"We think this dolphin has found a workaround to what is most likely a pathological problem," Dawson was quoted as saying.
