The Canary in the Coal Mine

A sentinel species is a type of animal that is used to detect environmental risks to humans.  The sentinel animal is affected before humans are.  One example is cats.  Cats are more susceptible to mercury poison.  In Minamata Bay, Japan, cats developed “dancing cat fever” when exposed to too much mercury.  The sick cats imply that there is too much mercury in the fish meat.

But, by far the most famous example of sentinel species is the canary in the coal mine (probably because of the idiom).  Canaries were carried into coal mines as a warning for dangerous gases, especially carbon monoxide.  If the bird dies, the miners knew to evacuate immediately.  The earliest mention of this practice dates to 1906.  By 1915, the canary in the coal mine was being used as an analogy.  The practice of bringing canaries into the mines was halted in 1986 in Britain.

While human miners are being phased out of the mining industry, the phrase a canary in the coal mine has stuck around.  Nowadays the phrase refers to a warning sign that should not be ignored.  The phrase implies that if we don’t acknowledge the warning, the consequences are dire (very bad).

Example:  Greenland’s disappearing ice is the canary in the coal mine for climate change. 

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Reference:
https://en.wikipedia.org/wiki/Sentinel_species
https://www.smithsonianmag.com/smart-news/story-real-canary-coal-mine-180961570/
https://wordhistories.net/2018/03/31/canary-coal-mine/
https://www.reuters.com/article/us-climate-change-arctic-idUSKCN25A2X3