The Dark History Behind the Phrase ‘Canary in the Coal Mine’

In 2013, as certain butterfly populations plummeted across North American prairies, Canadian conservationist Cary Hamel explained why people should care.

“Butterflies are a bit of a canary in a coal mine,” he told The Canadian Press. “They’re really sensitive to changes in weather. They’re sensitive to changes in habitat loss. They’re sensitive to invasive species and land management. The fact that the Poweshiek skipperling and other prairie butterflies are all declining should really have us stand up and take notice that something is going wrong with our native prairies.”

It’s a textbook example of a canary in a coal mine: something that serves as an early warning sign of a larger issue. These days, anything can fit the bill, from the aforementioned insects indicating a troubled ecosystem to struggling small businesses indicating a troubled economy.

But the original canary was a literal one—and it didn’t indicate trouble in a coal mine by chirping.

1. From Pet to Pit
2. Miner’s Best Friend
3. The Canary After the Coal Mine

From Pet to Pit

Mines are a hotbed for dangerous gases collectively known as damps—from Dampf, the German word for “vapor.” Hydrogen sulfide is stinkdamp, so named for its rotten-egg-like odor; the ever-flammable methane makes up firedamp; a carbon dioxide mixture is black damp because flame lamps won’t stay lit in those conditions; and carbon monoxide, the invisible killer, is white damp.

The cocktail of gases produced by a mining explosion (i.e., the afterdamp) often features carbon monoxide, and rescue missions can’t succeed or even proceed without knowing whether the atmosphere is unsafe. Before modern detection technologies existed, people relied on canaries to tell them. 

The idea is generally credited to John Scott Haldane, a pioneering British physiologist whose experiments—some done on himself and his teenage son—gave us oxygen therapy and a greater understanding of how various gases affect the human body. (The family motto was “Suffer.”) In the late 19th century, Haldane observed that small, warm-blooded animals are affected by carbon monoxide poisoning much more quickly than humans. He recommended that men use them as a natural alarm system in mines.

But celebrating Haldane as the sole genius behind so-called “pit canaries” poses a couple of problems. For one thing, his initial reports in the 1890s centered on the use of mice. Only in the early 20th century, when the existence of pit canaries was already hitting print, did he start mentioning birds in his published work. Moreover, researchers have pointed out that canaries had accompanied miners for decades, if not centuries, before the practice went mainstream. According to writer Jerry Dennis, Austrian Alpine miners adopted canaries as early as the 1690s, and some brought the birds with them when they later migrated to Germany’s Harz Mountains in search of work. Harz miners began breeding canaries to sell as domesticated songbirds—a side hustle so successful that by the 19th century, the region was a premier canary exporter.

All that said, Haldane’s science-backed endorsement of little creatures in general as carbon monoxide monitors no doubt helped legitimize and institutionalize the custom. A 1911 British law mandated that every mine with at least 100 underground workers keep “two or more small birds” on hand. It’s unclear exactly how canaries so quickly eclipsed other birds as miners’ choice companions, but what made them such a popular pet probably also made them such a popular mining tool. They were singsongy, sociable, bright-yellow birds—the kind you’d notice going sullen and dropping from its perch, even in darkness. That’s what they did when exposed to carbon monoxide, signaling rescuers to beat a hasty retreat.

Miner’s Best Friend

Pit canaries didn’t perish on every journey underground; plenty were revived once they had clean air in their lungs, sometimes thanks to a special cage outfitted with an oxygen pump. But it was hardly a risk-free gig, especially for canaries reused on mission after mission. “In the office of Francis Keegan, state mine inspector, sings a little yellow canary—weakly, very weakly.” one Kansas newspaper reported in 1914. “It hops feebly about but soon tires and returns to its cage. It is waiting to die so that some men may live. … Perhaps the next trip into the mine will be its last.”

Officials did test out other animals. Sparrows briefly seemed promising as “comparatively little sentiment attaches to” them, as Texas’s El Paso Herald put it in 1912, but one mining report claimed that they “do not lend themselves easily to captivity.” The Herald also explained that mice didn’t suffice “because when confined in cages, they are liable to sulk, and it is not always possible to know whether their behavior is attributable to this cause or to gas distress.”

Some coal mines, according to a 1913 story out of Washington, D.C., employed “nimble and sinewy” rats to run on tiny treadmills, “presumably after a bit of cheese forever out of reach.” The treadmills powered lights—convenient in dark mines—and if the light went off, it was immediately clear that your rat may have inhaled noxious fumes. But none of these alternatives could quite compete with the tried and true canary. World War I tunnelers, many of whom were miners by trade, even used the birds to detect gas as they hacked toward enemy territory.

Canaries continued to participate in mining operations for the better part of the 20th century; Britain didn’t stop requiring mines to keep them on site until the mid-1980s. Some miners were loath to see their feathered friends replaced with electric monitors. “There is no more reassuring sight down a mine during an emergency than seeing a canary sitting happily on its perch. Anyway, I would much rather trust a bird than batteries,” one former miner told the Leicester Mercury in 1986.

The Canary After the Coal Mine

Canaries’ mining legacy lives on in the phrase canary in the coal mine (and other iterations, e.g., canary in a coal mine), which gained more widespread popularity toward the end of their tenure underground. The Oxford English Dictionary’s earliest citation is from a 1970 journal article in Audubon: “The epidemic rise of emphysema plus a plague of respiratory diseases—these are but the canary in the mine. They alert us to the ultimate catastrophe.”

But the expression existed at least a little before then. Kurt Vonnegut used it in an address to the American Physical Society in February 1969:

“I often wondered what I thought I was doing, teaching creative writing, since the demand for creative writers is very small in this vale of tears. I was perplexed as to what the usefulness of any of the arts might be, with the possible exception of interior decoration. The most positive notion I could come up with was what I call the canary-in-the-coal-mine theory of the arts. This theory argues that artists are useful to society because they are so sensitive. They are supersensitive. They keel over like canaries in coal mines filled with poisonous gas, long before more robust types realize that any danger is there.”

Vonnegut mentioned his “canary-bird-in-the-coal-mine theory” again in a 1973 interview with Playboy. Artists, he explained, had “chirped and keeled over” in reaction to the Vietnam War before society at large had cottoned on to its horrors.

While figurative canaries can be found in any sphere, many live in the natural world. Sentinel species, as they’re known, are organisms that scientists track in order to learn about the broader well-being of an ecosystem—including threats that can, like carbon monoxide in a mine, endanger humans. Mussels clue us in to water contaminants, and lichens know whether we’re breathing dirty air. Sentinel species can also help industries operate more effectively and less disruptively within ecosystems; the weight fluctuations of northern elephant seals, for example, can tell fisheries more about where and when to fish than you might have thought.

The canary’s own watch may have ended, but it gave us an easy way to grasp what sentinel species do. In fact, they’re even sometimes called “ecosystem canaries.”

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