Canary

A canary is a type of Earth bird native to the Canary Islands.

According to Jonathan Archer, "miners used to take canaries into the tunnels with them. If the canary didn't die, the miners knew the air would be safe to breathe, and they could proceed." This analogy was made in reference to the Sphere Builder who was discovered in a transport pod as part of an experiment designed to monitor his exposure to normal space. 

Thadiun Okona once joked that "life is like loading twice your cargo weight onto your spacecraft. If it's canaries and you keep half of them flying all the time, you're alright."