We might not be able to hear them without the use of sophisticated technology, but humpback whales are loud. Don’t take my word for it. Listen to this recording:
They call to one another to gather in groups and males sing their hearts out to attract females. So after decades of listening to and studying their songs and other vocalizations, scientists were surprised to learn that these whales sometimes “whisper.”
Humpbacks migrate long distances between foraging and breeding grounds and sometimes the moms don’t get much time in the “nursery.” While in their breeding grounds, pregnant females need to be efficient about giving birth and adequately nursing their calves so that they are strong enough to tolerate the long return migration to their foraging grounds. Scientists didn’t know much about the nursing behavior of cetaceans, so Simone K. A. Videsen and colleagues decided to investigate.
They used non-invasive, multi-sensor tags on eight young humpback whale calves and two mothers. These tags collect a variety of data, such as their depth in the sea, their movement, and their vocalizations.
From the data they collected they figured out how much time (about 20%) humpback whale calves spend nursing while on the breeding grounds. But even more interesting was the discovery that the whales “whisper.” Prior to their study, the scientists assumed that the calves would call out to their moms when they wanted to nurse, but the data they collected told another story.
When a mother and calf communicate, they do so at a much lower amplitude than those produced by adults in the same area. Scientists think that the whispering may reduce the risk of being heard and pursued by killer whales or being heard and harassed by male humpback whales.
Although this whisper strategy may serve to protect the whale babies, it has its downside. It’s possible that the noise made by ships passing over breeding grounds might drown out the whispered contact calls and cause mother and calf to lose track of each other and separate.
This important research tells us that the humpback’s breeding areas should be preserved and protected in order to keep mothers and calves together during this critical nursery period. Read the paper to learn more.