The nesting area of the endangered whooping crane appears to be expanding.

Four pairs have been found outside of their traditional area in Wood Buffalo National Park this year.

Brien Johns, a biologist with the Canadian Wildlife Service, spotted 54 nesting pairs in a recently completed aerial survey of the birds.

"Whooping cranes are territorial birds. They don't tolerate other cranes on their territory or nearby. They'll actively chase off birds," he says.

"The main nesting area is along the Sass and Kluey Rivers . It's not getting real full but the concentration of birds is increasing enough that birds have to spread out a bit."

Johns says nesting whooping cranes require a lot of space.

Each pair needs an average of 4.5 square kilometres.

Johns says there is substantial habitat to the north of Wood Buffalo National Park that could be occupied by whooping cranes.

In 1941 there were only 15 whooping cranes left in the world.

Today there are over 400, with about 216 in the wild flock that nests in Wood Buffalo National Park.