Have you ever heard the phrase “canary in a coal mine”? The term is used as an early warning of danger, and dates back to the early 1900s. John Scott Haldane suggested using a sentinel animal to give a warning to miners about carbon monoxide leaks.
The animal the miners chose was the canary, a bird more vulnerable to poison gas due to their rapid breathing rate, small size, and high metabolism. The canary acted as an evacuation signal for the miners. If the canary died, that meant there were poisonous gases present. Canaries also boosted the morale of the miners because they would whistle to the birds and treat them like pets.
The last canary used in a mine was in 1999 and was replaced by electronic noses, a type of poison gas detector. The older phrase is still in use today, like when Secretary of State John Kerry referred to climate change as the canary in a coal mine. Even though canaries are no longer in use in mines, their usage serves as a reminder of our history.
[Sources: Smithsonian; Wikipedia; ShareAmerica]