Researchers say they have shown for the first time that humpback whale calves make sounds. The nonprofit Cetos Research Organization, which studied humpbacks off Maui and Kauai, say the grunts and squeals emitted by the young whales are messages for their mothers.
Ann Zoidis, director of the research project, said the sounds may be expressions of curiosity or warnings of potential danger.
The sounds are not as complex as the continuous, repetitive and highly structured phrases and themes of older males, the researchers found.
The calves instead produced a limited number of sounds that were short and simple in structure, according to the study. The noises included repetitive grunts that increased in strength and were sometimes accompanied by bubble streams and seemed to function as an alarm call to the mother, the researchers found.
They say the sounds were produced more frequently during calmer periods when the mother was resting or during slow travel.
"This tells us that calves do in fact communicate, and it tells us they are communicating to their mothers," Zoidis said.
An article about the group's research, which was conducted during the winter months between 2004 and 2008, appears in the March issue of the Journal of the Acoustic Society of America.
Prior to Cetos' research, scientists had recorded sounds from whale pods that included calves. But Zoidis said they had difficulty pinpointing the particular animals responsible for the noises.
She said the common theory among scientists was that humpback calves did not produce sound.
She said Cetos researchers traced the sound back to its source, demonstrating that both male and female humpback calves make noises.
The group is continuing to study the sounds, including when they are emitted. The researchers are trying to determine whether they are a potential indicator of stress.