Migratory birds such as these snow geese could die if they come in contact with oil that has spilled in the Gulf of Mexico. (CP)

The massive BP oil spill in the Gulf of Mexico could kill off some of Alberta's migratory birds, an Alberta bird expert fears.

By the time the oil giant managed to put a temporary cap on the damaged well in mid-July, the U.S. government estimated that 4.9 million barrels of oil had spilled since the Deepwater Horizon rig explosion that began the disaster in April.

"Even a small amount of oil can be deadly, affecting the bird's ability to control its body temperature and to feed," Pat Kehoe, a provincial manager with Ducks Unlimited in Alberta, told CBC News.

"Certainly the Louisiana and Gulf Coast is a major wintering area, particularly for waterfowl. Over 13 million ducks and geese winter along the Gulf Coast every winter and an even higher number pass through the Gulf Coast.

"So as those birds pass through Louisiana and the Gulf Coast states, the risk of them coming into contact is of high concern," Kehoe said.

While the spill has not spread significantly through Gulf marshland in recent weeks, the concern now is hurricane season, Kehoe said. A major storm could churn up oil that has already sunk to the seabed and spread it inland.