There are now an estimated 300 cranes in Wood Buffalo flock, up from 16 in the 1950s. (Kathy Willens/Associated Press)

The world's number of whooping cranes are steadily on the rise, according to biologists at Wood Buffalo National Park. 

There are now an estimated 300 cranes in the flock, which is up from 16 in the 1950s.

Each winter, the birds migrate to Texas. In the spring, they return to the national park that spans parts of Alberta and the Northwest Territories.

Biologists survey the whooping crane nesting area from the sky each May in Wood Buffalo National Park. They counted a record number of nests this year.

"There were 82 nests located during the nesting survey, which is a record. That's the highest number of cranes ever counted," says ecologist Rhona Kindopp.

Biologists scan the wetlands for pairs of the tall, white and territorial birds. The cranes often return to the nesting site they used the year before. But the birds choice of nesting site isn't their only display of loyalty. 

"They do establish long-term relationships. But if they lose their mate they will find another one," Kindopp says.  

She says numbers are up, in part, because the birds are so closely monitored. No one's been allowed to hunt them for decades. Their habitat in Wood Buffalo and in Texas is protected. 

"This is the one and only viable population in the world, so any catastrophic event that could affect this population affects the world's population of whooping cranes."

Kindopp says wildfire works in the cranes' favour because it pushes back trees and creates more ponds for nesting.

The next whooping crane survey happens in early August. Park staff will do aerial surveys again to count fledglings.