Babies are known to be very vocal in their cries for garnering the constant attention of mothers. However, a new study says baby humpback whales communicate with their mothers in "whispers" that is hardly audible to anyone except the mothers.

This was revealed in a study conducted by ecologists from Denmark and Australia. The study was examining the life of baby humpback's whales in their early months after birth.

According to lead author Simone Videsen of Aarhus University, there has been very little knowledge on the early life of whales in the wild.

The early months are crucial in the life of the calves with regard to survival and long migration to feeding grounds.

To decipher the communication, the researchers placed microphone tags on eight humpback whale calves and two mother whales at the Exmouth Gulf off Western Australia.

What Do The Recordings Say?

Normally, humpback whales sing aloud. The microphone tags, however, showed that calves were uttering intimate grunts that are audible at a close range while swimming with the mothers.

The DTAGS carried suction cups to record sounds for 48 hours. When listening to the recordings, procured from the tagged whales, the researchers concluded that the calves were not crying for food.

The sounds made by baby calves are a mechanism to stay in close contact with mothers while swimming. The low decibel sounds help the babies to ward off the gaze of predators away who may overhear loud sounds.

 "We ... heard a lot of rubbing sounds, like two balloons being rubbed together, which we think was the calf nudging its mother when it wants to nurse," said Videsen.

The study has been published in Functional Ecology.

According to the researchers, the hushed tone of communications can dodge predators and also male whales eyeing the mothers for mating and may disrupt the nursery.

Migratory Challenges Of Whale Calves

For young calves, the early days of life are strewn with many challenges and hardships. One of them is the long distance travel of an average 5,000 miles in open seas braving strong winds while moving to the food-rich Polar Regions.

Humpbacks spend their summer in the waters of the Arctic and Antarctic and migrate to tropics for mating and breeding during the winter. The calves gain weight to be fit for swimming in their first migration efforts at tropical waters like Exmouth Gulf.

In between the whispers of the newborn, the mothers also make quiet responses to calves. Considering the mothers' ability to vocalize louder, keeping the sound intentionally lower shows the concern for the safety of the babies.

Slow Reproduction Of Whales

According to studies, humpback whales have a slower reproductive phase. Pregnancies extend for a year and calves are in the size of 16 feet at birth with an average growth of 3.3 feet every month. The calves stay attached to the mothers for almost a year. Humpback whales are present in the northern and southern hemispheres.