Yukon's growing wood bison herd continues to elude Yukon hunters, as harvest reports are well below expectations with just three weeks left in the hunting season.

More than 900 bison permits were sold this season in Yukon but harvest reports to date show just 69 animals have been taken.

Environment Yukon biologist Tom Jung says the animals are simply unpredictable.

"One thing that's typical about bison is that every year is a little bit different," he said.

Jung spent the past few weeks radio collaring animals in the herd, and confirms hunter complaints that the bison are hard to find.

He says groups are congregating on snow-free hillsides.

"What we are seeing out there are conditions more typical of early April," he said. "There's not much snow on the ground and a lot of the hilltops are free of snow and unfortunately it's hard for hunters to get up there to get a bison."

Jung says aerial tracking flights Thursday will allow them to map the latest herd locations. That map will be published later this week to guide hunters to their quarry.

The last population census in 2011 showed the herd had grown to 1230 animals.

A new census planned for this summer should confirm whether the herd is still growing. 

A Bison Management Plan for the herd suggests the population should be held to around 1000.