Despite one of the largest animal population studies ever, what's killing Newfoundland's woodland caribou is still mostly a mystery.

The province launched its caribou strategy in 2008 to search for a cause for the island's plummeting caribou population.

Newfoundland and Labrador kept excellent data on caribou for nearly 100 years, but in 1997, the work of counting the animals abruptly stopped. When it resumed in 2003, researchers were shocked to discover that almost no caribou calves were surviving their first year.

To find out why, wildlife biologist Shane Mahoney has led a team of researchers who have studied everything about the caribou, including the animals' size, movement patterns and eating habits.

They've also been running parallel studies on the woodland caribou's three main predators: lynx, coyote and bear.

Preliminary results have suggested predation has played a large role in the population decline.

Mahoney has been using radio collars to track young caribou, which have often led him to kill sites, and piles of young caribou bones.

Biologist Shane Mahoney said the causes for the low caribou numbers are complex. (CBC)

At one set of bones in Newfoundland's Avalon Wilderness Reserve, Mahoney found a jaw bone, missing the piece where fatty tissue connected the jaw to the skull.

"This is one of the tell-tale signs of a black bear kill," said Mahoney. "Lynx do not do this, coyotes do not do this, and bears pretty well always do this when they kill a young caribou."

Big study, few answers

Universities across North America have been helping Mahoney analyze specimens from kill sites. The caribou strategy has become one of the most comprehensive studies ever of an animal population, costing $15 million, and taking almost five years.

But despite all this work, Mahoney says the Newfoundland woodland caribou population is still too low. "Even here, three weeks post-calving, a significant number of calves have already been lost," remarked Mahoney, surveying a herd of about 300 caribou inside the Avalon Wilderness Reserve.

The rate of calf mortality hit a shocking high of nearly 100% in 2003.

Today, only about 30% of caribou calves survive, well below what's needed for a stable population.

Mahoney has found no easy answers.

"It is never a single cause and effect, it is always complex," said Mahoney. "And what we're trying to do in this research is tease apart the various influences that are responsible for this."

The completed caribou study will be released in 2013.