As you move north from the broad reaches of Great Bear Lake in the Northwest Territories of Canada, spruce forests first give way to scrubby taiga, then to the hard, smooth rocks of the Canadian Shield, and finally to the southern Arctic. This is the Sahtú region.

It is caribou country. The Dene and Métis people have coexisted with the caribou for millennia.

Now it seems that these people may have known something about the caribou that science has, so far, missed. Ecologists know about three groups of caribou in the Sahtú, each with a different lifestyle and habitat. But the Dene say there are four, and a new study may offer some support for their belief.

Caribou are deer that live in the far north of North America. They also range into northern Europe and Asia, where they are known as reindeer.

The scientific community recognizes two subspecies of caribou in the Sahtú, known as "barren ground" and "woodland" caribou. The woodland caribou are further split into "mountain" and "boreal" groups, which are genetically similar but have different lifestyles. That gives a total of three.

The Dene and Métis people have coexisted with the caribou for millennia

However, in a study published in February 2016, ecologist Jean Polfus of the University of Manitoba in Winnipeg, Canada and her colleagues found that in other areas there was a lot of genetic mixing between the three caribou groups. This suggested that the same might be happening in the Sahtú.

A lack of clear divisions between the types could have big implications. "Different types of caribou have different statuses under the Species at Risk Act," says Polfus. "If the variations below the species level aren't accurately described, the related conservation or policy actions could be ineffective."

This is especially important as boreal woodland caribou are territorially and federally listed as a threatened species. This status requires governments and other wildlife managers to act to protect them. But in the other areas Polfus studied, the genetics suggested they were not really that distinct from the other groups.

To try to resolve the question, Polfus turned to the Dene and their traditional knowledge.

In 2012, Sahtú's five Renewable Resource Councils (RRCs) ­­– community-level organizations charged with wildlife management – passed a resolution encouraging caribou researchers to use local knowledge.

All across the Sahtú, the Dene have a name for boreal woodland caribou: "tǫdzı"

In line with that, Polfus began studying the Dene language and the way the Dene describe the caribou groups.

"Being able to effectively hunt caribou was critical to the survival of the Dene," says Polfus.

As a result, they have always paid close attention to the animals. "They have language and traditional knowledge that describes the different kinds of caribou, but also the history of their range movements," says Polfus. "This helps us better interpret our genetic data."

All across the Sahtú, the Dene have a name for boreal woodland caribou: "tǫdzı". The language describes them as having a unique habitat and appearance, and even behaviours – all of which differ from both the "ɂekwę́" ("barren-ground") and "shúhta ɂepę́" ("mountain") caribou. These terms are used broadly by different cultural groups and in different Dene dialects.

People wouldn't have a word for this type of caribou if there wasn't something unique about them

"They describe [the boreal woodland caribou] as being different," says Polfus. "They are harder to hunt and bigger than the barren ground caribou, and there's specific language around how to hunt them."

Polfus collected genetic samples from the boreal woodland caribou and found that they really are a genetically distinct group; consistent with the way the Dene language described them.

Polfus and her colleagues have published their results in the journal Ecology and Society.

The team's exploration of the Dene language also introduced them to a mysterious caribou not named in western science: the "Tęnatł'ǝa" or "fast runners."

Leon Andrew is Dene and works as an advisor to the Sahtú Renewal Resource Board, which works with the RRCs to manage wildlife across the region. He remembers family members talking about the Tęnatł'ǝa.

"They came from the ocean," he says. "That's how they described it." Andrew has never seen one, but says the elders told him that this caribou has ears more pointed than others. "We know they are out there," he says. Now they just need to be found.

They are harder to hunt and bigger than the barren ground caribou, and there's specific language around how to hunt them

"People wouldn't have a word for this type of caribou if there wasn't something unique about them that was important to describe, for example something important for hunting," says Polfus.

The Sahtú Renewal Resource Board met in September 2016 to determine new caribou research priorities. They will continue to search for the Tęnatł'ǝa.

Polfus's work demonstrates the power of combining science and traditional knowledge. The Dene call this "Łeghágots'enetę": "learning together."

"It's fun to tie in different disciplines, and look at the strengths of examining the world from different perspectives," says Polfus. ­"There are different ways of categorising the world and looking at patterns of biodiversity."

Join over six million BBC Earth fans by liking us on Facebook, or follow us on Twitter and Instagram.

If you liked this story, sign up for the weekly bbc.com features newsletter called "If You Only Read 6 Things This Week". A handpicked selection of stories from BBC Future, Earth, Culture, Capital, Travel and Autos, delivered to your inbox every Friday.