Four bald eagles found poisoned near the Campbell River, B.C., landfill last week have been released back into the wild, but a fifth more seriously ill bird is still in treatment.

Blood tests confirmed the eagles had overdosed on barbiturates after feeding on the carcass of a dog that had been euthanized and dumped at the landfill, according to Maj Birch of the Mountainaire Avian Rescue Society.

Birch said barbiturate poisoning isn't uncommon in eagles, and the owners of euthanized pets should ensure they are cremated or properly buried, to prevent it.

"It's really important that they take very good care of burying their pet deeply, putting rocks on top," Birch said. "I plant trees on my pets so that you can go back and visit it on a regular basis. It's really important to just take caution because other animals can dig them up and become affected by that drug."

Barbiturates are a controlled substance and veterinarians need to be more aware of where the powerful sedative goes, Birch added.