A cacophony of squeaks, clicks and whistles erupts from the frigid waters of Cunningham Inlet in the Canadian Arctic. Though reminiscent of squeaky bath toys, these squeakers are very much alive. Swimming at the surface are hundreds of icy-white beluga whale mothers, their small grey calves hugging their sides.

Nicknamed "canaries of the sea" by early whalers, belugas' squeaks and squawks are critical to their survival. It's their main form of communication, as they live in a habitat that is nearly pitch-black for half of every year. "They are navigating under ice, in dark waters, so they are completely reliant on sound," says Valeria Vergara of the Vancouver Aquarium in British Columbia.

Their communication system is startlingly complex, and scientists like Vergara are beginning to unravel how it works. They can now eavesdrop on the belugas, revealing clues to what they are saying. But looming over all this is the threat posed by noisy humans, with our ships and the banging air guns we use to search for oil and gas. The question now is, will the belugas still be able to talk to each other when their homes are drowned in man-made sound?

Among whales, belugas are one of the most vocal. A group of belugas makes a noise a bit like a crowd of children shouting in the distance.

If you get close enough to hear individual calls, you will realise that they make a variety of strange sounds. Beluga calls variously resemble a cork being prized from a bottle or a creaking door, along with sounds described as clicks, squeaks, chirps, bleats, moans, groans, and whistles. In 2012, scientists reported that a captive beluga had learned to make what sounded like garbled human speech, presumably in an attempt to mimic its human neighbours.

Belugas can wiggle their melon

It's not just about communication: belugas also used sound for navigation. "Sound to them is like eyes to us," says Vergara. Like other toothed whales and many bats, they use echolocation: they make a rapid string of clicks that bounce back from the environment, and interpret the echoes to identify objects such as food.

Belugas make all these sounds despite having no vocal cords. Instead they "speak" through nasal sacs near their blowhole. In essence, they talk through their noses.

They can also carefully direct their sounds, using a fatty deposit called a melon located between a beluga's blowhole and snout, on its "forehead". Unusually, belugas can wiggle their melon – yes, really – and this may help them fire sounds in specific directions.

To find out how beluga communication works, Vergara spent five weeks in the summer of 2014 in a leaky yurt perched on the edge of a cliff next to Cunningham Inlet. About 2000 beluga mothers and calves spend their summers there each year. Vergara found that they form kindergarten groups, with 10 to 15 young calves playing and socialising under the care of a few watchful adults. They all talk non-stop.

The youngsters must learn from their elders

It is not just the mothers that take care of the calves. They get lots of help from "allomothers"; a community of sisters, cousins, aunts, and grandmothers. Many of these females start producing milk when another female's new baby is born, even if they themselves have no nursing infant. So baby belugas have a veritable buffet of milk at their disposal.

Vergara's work suggests that baby belugas may learn to call in the same way human babies do. "Baby belugas are not born knowing this beluga repertoire of sounds, just as we're not born knowing how to speak," says Vergara. The youngsters must learn from their elders.

What's more, it seems they learn in a similar way to human babies.

Vergara started by focusing on captive animals at the Vancouver Aquarium before testing her findings in the wild. Her research revealed that belugas make barely audible sounds within an hour of being born. The babies start making simple whistles within a few weeks.

It takes babies one to two years to develop perfect renditions of the contact calls

But as well as whistling, Vergara discovered that mothers and babies also use another kind of call, from soon after birth. It sounds a bit like running a finger rapidly along a plastic comb, and Vergara thinks it is a way of keeping in contact. In effect, mothers are saying "hello, I'm here, where are you?" and their babies are replying, "I'm here, I'm here" or "Mommy, come over".

Baby beluga vocal repertoire starts out simple and becomes more complex and varied over time. It takes babies one to two years to develop perfect renditions of the contact calls, Vergara has discovered.

In this, young belugas are similar to human babies, who babble and make rudimentary attempts at word segments before being able to fully form words, and then sentences.

"Cunningham Inlet is one of the most pristine beluga watching areas in the world," says Vergara. As a result its belugas appear to be holding their own. But elsewhere numbers are dwindling.

Scientists now suspect that noise is one of the factors contributing to their decline

Away to the south in Cook Inlet, Alaska, belugas head in from the Pacific to feast on salmon that swim up its rivers during the summer. A survey in the 1970s estimated there were about 1300 belugas in Cook Inlet. By 1994, there were 650. "Our most recent abundance estimate was 312 animals," says Rod Hobbs of the National Oceanic and Atmospheric Administration (NOAA).

Scientists now suspect that noise is one of the factors contributing to their decline. Cook Inlet is a busy harbour for Alaska's largest city, Anchorage, so the waters ring to the high-intensity pile-driving noises of port expansion, shipping traffic, and seismic surveys for oil and gas exploration – not to mention an airport, plus army and naval bases. For animals that navigate and communicate using sound, Cook Inlet is a noisy place.

Of course, the ocean has never been quiet. Belugas have always had to contend with noise like cracking ice, underwater earthquakes, and storms, but they've had thousands of years to adapt to these natural sounds. "The reason this [new human-caused] noise is so much of a problem today is that the animal has not had time to adapt to it," says Robert Michaud of the Group for Research and Education on Marine Mammals.

When marine mammals are exposed at close range to a loud sound, such as navy sonar, they can be rendered temporarily deaf, just like humans who have been to a rock concert. "After you leave you don't hear as well for a little while," says Aran Mooney of Woods Hole Oceanographic Institution in Massachusetts, who identified the effect in dolphins in 2009.

When the problem is one of constant noise, belugas act just like humans at a cocktail party. If you're in a room with lots of people talking, you can change the pitch of your voice or speak up so that people can hear you. Belugas do the same. In the St. Lawrence River in Québec, belugas responded to boat noise by temporarily "speaking" louder.

Researchers scooped out floating whale poop with the aid of sniffer dogs

But there are limits. Once a certain noise threshold is crossed, whales can't compete, and their sounds are drowned out, a phenomenon called masking. In the St. Lawrence, noise is thought to be one of the contributing factors as to why this population, considered endangered, is in decline.

There is some evidence that noise stresses whales. In the immediate aftermath of 11 September 2001, there was reduced shipping traffic in Canada's Bay of Fundy. An opportunistic study of right whales revealed a short-term but detectable drop in oceanic noise levels, which coincided with a measurable reduction in the whales' stress levels. To show this, researchers scooped out floating whale poop with the aid of sniffer dogs, and measured levels of stress hormones within.

The belugas' plight is increasingly urgent. As Earth's climate warms up, thanks to humanity's greenhouse gas emissions, the Arctic ice is melting and passages are opening up. "There's going to be more shipping, more resource exploration and more human usage of the Arctic," says Mooney. All those activities bring more noise, "so we want to know how sensitive or potentially sensitive belugas may be." He is now giving them hearing tests to find out what they can and can't hear.

As we learn more about beluga calls and hearing, we can figure out exactly how they are threatened. If human activities make high-pitched noises, it might interfere with echolocation and disrupt the whales' ability to feed and navigate. However, if we make lower-frequency noises, Hobbs says, "it's going to affect their ability to communicate as a group or over long distances."

Many beluga populations are restricted to specific areas

Baby belugas may be at particularly high risk. Their calls are very low-energy, narrow-band sounds, says Vergara, "which means that they could be more easily masked by noise." So mothers and calves could become separated in noisy environments.

Vergara's research site at Cunningham Inlet is one of the few beluga habitats not affected by man-made noise. That means Vergara is eavesdropping on "normal" mother-calf communication, which should help her colleagues understand what is happening to belugas in noisier places.

With that information to hand, she hopes to figure out what we might do to minimise the effects of our din. But according to Mooney, the solution might be quite simple. Many beluga populations are restricted to specific areas, he says. "So maybe we need to make those areas noise-free zones."

Otherwise, our noise might eventually drown out the squeaks of the belugas.