The birds were found dead or dying in 2015 at an abandoned sump pond at Syncrude's Mildred Lake mine north of Fort McMurray.

Two new federal charges were laid against Syncrude Canada in connection with the deaths of 31 great blue herons two years ago.

It is the largest heron colony in the world. But biologists had their doubts that the Great Blue Herons, which has resided in Stanley Park, would return to raise their young again this year.