The massive kill occurred between Friday night and Saturday morning at the Canaport LNG's plant in Saint John, New Brunswick, company health and safety manager Fraser Forsythe told the Canadian Broadcasting Corp.
Don McAlpine, head of zoology at the New Brunswick Museum, told the network the birds were drawn to the flames from the liquified natural gas plant's 100-foot-tall flaring tower like moths to a light.
It was foggy and overcast at the time, which may have contributed to the unusual event, McAlpine said.
"They would circle in around that and of course with a large flame like that and high temperatures, they wouldn't have to get terribly close to get singed or burned," he said.
About 6,800 of the birds were killed by the heat and several hundred more had to be put down because they were injured.
"There were too many birds to count," McAlpine said.
Forsythe said Canaport LNG employees were upset when they found the birds Saturday morning.
"We've got people reduced to tears here," Forsythe said.
Efforts were still going on Tuesday to identify the species and clean up the carcasses, the CBC said. It is possible some of the birds were endangered species, the network said.