Elizabeth: It’s 1926 and you’re in a mine cage, a type of elevator contraption that slowly descends down the shaft of a coal mine. The air gets colder and colder as the light disappears from above and you are plunged into darkness, lit only by a single dim bulb attached to your helmet.

The dank air feels cool and smells like dirt and wetness. Even with this silly breathing tube contraption you’ve got on your face, you can still smell the mine. You do this descent daily and the innate panic your body’s defense mechanisms should kick on as you plunge into the depths is only a whisper now. This is just a routine trip for you, checking the air quality before your crewmates head down. You chuckle as you think what Millie, your wife, would say if she saw you in this get up. There are leather straps with two buckles holding two metal and canvas tubes against your mouth. The tubes run along each side of your head, draping over each shoulder and connecting to a big, hard, yellow backpack attached to your shoulders with more straps. This thing will keep you breathing if things go south down there, or if tweety here starts acting kooky.

Looking down at the small box you are carrying you smile at your little buddy, a small yellow bird named Seymour. Contemplating such a serious name for such a small, insignificant animal you hum a tune as the steel wire rope lowers your cage further down and down into the depths. But little chirping Seymour is not insignificant. That bird will save your life, and the lives of hundreds of others down in these mines.

Finally the creaking cage comes to a stop at the bottom of the shaft. You Seymour’s little cage down for a minute and heave the squeaking metal gate aside. Picking up Seymour you step out onto the slick ground. Humming with Seymour as he chortles in the small cage you carry him in, you walk towards the end of this tunnel to begin your shift.

Marissa: The term “canary in a coal mine” is ubiquitous for any early warning signal. Like our fictional vignette of a miner carrying a canary into the coal mine, canaries were often taken into mines during the first part of the 20th century to test the air for poisonous gasses. The practice was so commonplace that it’s become a cliche. The canary in the coal mine is now a metaphor for something horrible about to happen whether it be a financial crisis, a world health issue, or the whims of fashion.

Elizabeth: Metaphors aside, canaries are a sentinel species, used by humans to detect environmental risks by providing advance warning of a danger. Often animals are used as sentinels because they are more susceptible to environmental hazards that humans may be in the same environment. In the case of coal mining, canaries — or really any small bird — are very susceptible to changes in air quality because of their rate of respiration, anatomy, and small size.

Marissa: Contrary to popular belief, canaries in coal mines do not have a very long history. They were only used as sentinel animals in British and American coal mines for roughly 100 years. In the grand scheme of things, that’s not a long time at all. Yet, canaries have become ubiquitous with mining in general and as a figure of speech.

I’m Marissa

And I’m Elizabeth

And we are your historians for this episode of Dig.

Elizabeth: So we’re doing this animal series at the behest of Marissa. Us Dig ladies were all in Boston at the Organization of American Historians convention and M had the bright idea of doing animals for our next series. And I thought mmmm okay? Needless to say, I wasn’t a fan and didn’t know what the hell I’d write an episode about animals on. However, I am planning a trip to Disney World and one of our favorite rides is Thunder Mountain. This is a roller coaster that is mining themed. The queue has some cool interactive doohickeys. Like you get to press some TNT boxes and water blows up out on the track. There’s also these contraptions that have a handle and if you turn it, you might see a canary inside that’s about to go down into the mine. It’s a fun, interactive queue line and with vacay on my mind I thought, Hey, I’ll do canary in a coal mine. Now full disclosure, I try to write episodes that I can use in my classes and I need a good mining and labor lecture so I figured I’d write an episode all about mining in America and just throw in the canaries for good measure. However, when I actually got to researching I realized that mining labor history books don’t really talk about canaries in coal mines. Searching through all of my go-to mine and labor books I didn’t find one that mentioned canaries in coal mines. Which, frankly, I thought was kinda weird. Or, if they did mention a canary it was just that- a mention- with no explanation or context. So then I went to the Google machine and got a lot of weird hits, read some blog posts, watched a few YouTubes and realized that there is not much peer-reviewed work about this subject, at least in the academic historical sense. Sure there are a lot of blogs and amateur history sites that brush over the subject, but not much I could really count on. Let me give you an example, anecdotally many web sites said canaries were used in the 1800s. A lot of these sources share a picture of Little Joe. Little Joe is a deceased canary encased behind glass, inside a wooden coffin-shaped box. The inscription on the front of the box says, ‘In Memory of Little Joe. Died November 3rd 1875. Aged 3 Years.” I found multiple websites and even a peer-reviewed article in a veterinary journal that said Little Joe is an example of a beloved coal-mine canary. However, Little Joe died twenty years before canaries were officially used in coal mines. There’s also no indication on his little coffin that he was used in a mine, just that he was someone’s beloved bird. So, as I researched and wrote this episode I learned a lot about mining science, particularly in regards to respiration, but I also witnessed how one wrong statement can be picked up over and over again and touted as fact.

Marissa: It’s well understood that mining has always been a dangerous pursuit, particularly when we take into consideration that the things humans are mining for are not necessary for our survival. Do resources like coal, copper, silver, and sulfur make our lives easier? Sure! But humans can survive without them. However, the desire to mine the depths of the earth for resources of either convenience or monetary value seems a common trait among many peoples. The earliest known mine is the Ngwenya Mine, located near the northwestern border of Eswatini (Swaziland). Radiocarbon dating shows that humans were mining red and specular haematite, which can be made into paint for body modification and rituals, as long as 40,000 years ago during the Middle Stone Age. In later times the deposit was mined for iron smelting and iron ore export.

Mining in Potosí, an engraving from Theodoor de Bry in Historia Americae sive Novi Orbis, 1596

Elizabeth: In the Americas, the Spanish imprisoned Americas indigenous peoples to mine silver in Peru, present-day Bolivia, and Mexico. The mining and exporting of silver, copper, and gold in the Americas was a key component of Spain’s American empire and for a time made Spain the richest and most powerful states in early modern Europe. However, the manpower needed to dig and extract those resources was achieved by brutal working conditions for indigenous indians and imported African slaves.  

Marissa: So even though mining seems to be an ancient human practice, coal mining is a phenomenon connected with the industrial revolution. There are a few coal mines dating back to ancient China and the Roman Empire, but the massive commercial production of coal that we are familiar with is tied to the industrialization of the west during the 19th and 20th centuries. For example, American’s doubled their use of coal every decade during the mid to late 19th century and by 1900, coal provided 70% of the nation’s power.[1] These numbers were similar for the UK.

Elizabeth: In Britain, deep shaft coal mining began to develop extensively in the late 18th century, with rapid expansion throughout the 19th century and early 20th century. Shaft mining is the excavation of a mine shaft from the top down. In 1862 at the Hartley Colliery in Northumberland, England a horrible accident caused the shaft to become blocked, trapping and killing 204 men and children in the depths of the mine. Most appeared to have died from asphyxiation. This prompted a British law requiring all collieries, or mines, to have two points of escape.

The calamity at the Hartley Colliery, bringing the dead bodies to bank
Illustration for the Illustrated Times, 1 February 1862. No 357. Vol. 14. Public Domain

Marissa: All mining is dangerous but coal mining has particular safety issues that must be contended with. Coal mining releases methane, known to the miners as “firedamp,” which is highly explosive under certain concentrations. Coal dust was even more dangerous, which could cause an explosion that could be triggered by firedamp ignition. These explosions consume oxygen in the mine and leave behind a toxic combination of odorless carbon monoxide and carbon dioxide known as afterdamp. Many explosions were caused by miner’s lamps igniting the firedamp.

A View of Murton Colliery near Seaham, County Durham. John Wilson Carmichael, 1843. Public Domain.

Elizabeth: Before battery operated lightbulbs, miners often carried open flames into mines as their only source of light. They might have candles or a hanging lamp that they placed on the ground or stuck in crevices. After roughly 1850, miner’s wore cloth or canvas hats that had a leather brim and metal brackets on the forehead where a miner could hang a small lantern from the front of his cap. Early versions of the lamps were created in Scotland around 1850 and looked like small tea kettles with a spout. The body of the lamp held oil and a flame could be ignited at the spout. These oil-wick cap lamps gave off just enough light for miners to see what was directly in front of their face, but not much else. They were also extremely smoky and sooty.

Marissa: In 1820, Sir Humphrey Davy invented the Davy safety lamp when he discovered that surrounding a flame with metal mesh prevented the combustion of the flame and surrounding gase. Safety lights were large and a bit cumbersome, so were not hung from a cap but were carried by hand into a mine. They served as both a dim light and as a detection mechanism as gasses in the air would make the flame in the lamp flare up but not ignite. This could alert miners to a firedamp area and they could evacuate. However, illumination from these lamps was very poor and often miners preferred a more open flame so that they could see what they were doing and frankly, make their days wages. Since most miners were paid by what they were able to dig up, sometimes safety had to be put by the wayside.

Elizabeth: Invented around 1910, the Carbide lamp provided a bit more light to miners. This lamp was also suspended from the brim of the miner’s cap but it used acetylene gas, which burned brighter and more cleanly than the oil wick lamps. Carbide lamps also normally had a reflector attached, which provided more light for the miner to see. However, both of these cap lamps still used an open flame as a light source and were therefore very dangerous to use in methane producing mines.

Marissa: In the 1910s electric light mining helmets began to be used more and more, eliminating some of the dangers that miners faced. Nevertheless, the job was still very dangerous and thousands of men and boys died in mining accidents throughout the 20th century. Besides explosions, a real risk to miners in coal mines was asphyxiation by poisonous gasses.

Elizabeth: In 1892, physiologist J.S. Haldane began to experiment with breathable air and respiration. He determined that “black damp,” which had been thought to be purely carbon dioxide “was actually a mixture of about 87% nitrogen and 13% carbon dioxide and was the residue left when the oxygen of air which had penetrated into the coal had been absorbed in the spontaneous oxidation of the coal.”[2] He demonstrated that  breathing is regulated by changes in the partial pressure of carbon dioxide in the blood. Through more experiments, Haldane became deeply committed to solving mining safety issues while also determining to understand human respiration when exposed to chemicals and gasses.

John Scott Haldane. Scottish physician and physiologist and winner of the BEST mustache award.

Marissa: Haldane soon turned his attention towards carbon monoxide poisoning in mines. Carbon monoxide is a colorless, odorless, and tasteless gas that easily binds to the hemoglobin in blood that can build up in the body and cause death and is a product of blasting, or present in afterdamp after a gas or coal dust explosion, or in the aftermath of a mine fire. In 1894 he visited the Albion Colliery after a horrendous explosion there and determined that of the 54 bodies recovered from the mine, only four had died from the immediate explosion. He determined the other 50 succumbed to carbon monoxide poisoning because of the high degree of carbon monoxide in their bloodstream. Because of the high saturation in their bloodstream, Haldane determined the miners must have remained alive for a considerable amount of time after the explosion, breathing in the “afterdamp.”  In 1895 Haldane published a paper on the effects of carbon monoxide inhalation.[3]

Elizabeth: Haldane spent the next several years determining how carbon monoxide kills human beings. He performed dangerous experiments on himself, breathing several toxic gasses in self-experimentation. He chronicled the ways in which his own body reacted to varying degrees of carbon monoxide poisoning. From these experiments he created a test that allowed for determining the level of saturation of the blood with carbon monoxide. Aside* there is a 2007 book written by journalist Martin Goodman for general audiences about Haldane’s self-experimentation, entitled Suffer and Survive: Gas Attacks, Miners’ Canaries, Spacesuits and the Bends: the Extreme Life of Dr. JS Haldane. I was unable to read this book because according to WorldCat there were no US libraries near me that had a copy, only Canadian libraries- the closest being in Toronto. It’s also not available on Kindle or ebook. I did however read a few reviews on the book, mostly from scientific journals, and although these reviews said the book was fun in looking at Haldane’s crazy self-experimentation, it got a lot of the science wrong.

Marissa: In 1896 Haldane submitted a report to the British Home Secretary where he suggested that miners should bring a small animal into the mines, like a mouse, because they have a high relative metabolism and will exhibit effects of carbon monoxide poisoning sooner than humans would. The report was immediately translated into several languages and caused quite a buzz. Soon, miners in the UK were routinely taking canaries into mines as a safety precaution. A 1906 newspaper article from the Nottingham Evening Post chronicled the use of a canary after a mine explosion.
“When the rescue party descended the mine a canary in a cage was kept in front and dropped off its perch when the danger point was reached, overcome by the poisonous atmosphere. This is a new use for the canary, and it is satisfactory to know that the bird recovered from the effects of the afterdamp, and was produced at the inquest.”[4]

The use of canaries proved so useful that in 1911, the Coal Mines Act was passed in the UK, which required miners to take “two small caged birds” into the mine with them. 

Elizabeth: As far as I can tell, there were no such laws in the US that required miners to take canaries or other small birds into the mine. However, there are plenty of photographs of US miners with canaries. Additionally, the US Bureau of Mines endorsed the use of canaries as a safety precaution, stating in 1914 that canaries were the best animals to do this work:

“The usefulness of small animals in detecting vitiated air in mines is well established. . .The [US] Bureau [of Mines] has experimented with most of the more common small animals, such as canaries, guinea pigs, rabbits, chickens, dogs, mice, and pigeons, and finds that canaries or mice are the most suitable for the work. Of the two the Bureau finds canaries to be the most sensitive. . . If handled intelligently in rescue operations, they rarely die as a result of their exposure to carbon monoxide.”[5]

Marissa: We’ve also linked a short video clip from 1926 that was produced by the US Bureau of Mines, touting how canaries are used as carbon monoxide detectors.

Mining rescue teams would keep several canaries on hand and in the event of an explosion or fire, rescuers would descend into the mine carrying a canary in a small wooden or metal cage. If the bird showed any signs of agitation of lethargy, this was a clear sign that all was not right and prompted a speedy return to the surface.

Elizabeth: When canaries are exposed to toxic gasses, particularly carbon monoxide, they initially become highly agitated- flapping and jumping around their cage. In extreme conditions they may faint and fall off their perch. The bird’s rapid heart rate and high metabolism allow it to react to the presence of carbon monoxide or methane about 20 minutes before a miner’s body is affected by the gas.

Marissa: Canaries particularly small size and rapid metabolism coupled with an incredibly efficient respiratory system make them an ideal bird for such work. All birds possess a paleopulmo system that makes up 75%- 100% of lung capacity. This system allows continuous air flow through the lungs, meaning that air enters the lungs on both inspiration and expiration. Additionally, in avian lungs the blood capillaries are arranged perpendicular to the walls of air capillaries, creating a gas exchange system that allow birds to extract oxygen very efficiently.[6] This, from what I understand, is what makes birds extremely sensitive to poisonous gasses in the air.

Elizabeth: But why canaries? Why not parakeets? Or finches? Researcher for Gale Primary Sources, Amelie Bonney, found a 1926 article out of Dundee, Scotland that said wild redpoll birds were used for mining over canaries because they are “more active, and more sensitive to the effects of gas than cage-bred birds.”[7] However, in photo after photo it’s canaries pictured in the cages so I wonder if this was just a fluke. However, this same article goes on to say how redpolls were collected for mining use. They were and were “caught…by bird catchers all over the country,” and were supplied to mining operations through “the bird markets.” Veterinarian Christal Pollock states that mining companies in the UK purchased canaries from ordinary pet shops, usually ones with poor coloration or other such imperfections that made them less desirable on the pet market. Also, apparently some mining companies built aviaries and bred their own birds for mine use.[8] The US Bureau of Mines stated that canaries are “generally easily obtainable, and become pets of the men who have them.”[9]

Mining foreman R. Thornburg shows a small cage with a canary used for testing carbon monoxide gas in 1928. George McCaa, U.S. Bureau of Mines. Public Domain.

Marissa: It is interesting that many of the sources I saw in newspapers that discussed canaries in coal mines were usually concerned about the welfare of the birds. Dugald Macintyre wrote in the Scottish Dundee Courier that the mining birds were “uniformly well cared for.” However, he went on to say that “Good as is the treatment of those life-saving birds, it seems a queer thing that in this age of science a proper hand instrument cannot be invented to take the place of the harmless and useful birds in testing the mines for gas. To see [the birds] go down on what is a present a necessary mission of mercy is pathetic, for the dark and gloomy pits are the very antithesis of the natural haunts of the joyous sun-loving ‘children of the air.’”[10]

Elizabeth: Anecdotally, the birds were friends and companions of the miners. Not only did they save their lives, but they, like Seymour from our vignette at the top of the show, were in fact the miners’ “little buddies.” Miners would whistle to the birds, or feed them little treats before their shift. I get it. As I write this episode, I’ve got a little parakeet in my office that I’m talking back and forth with. He’s a very “pretty bird.” *actually he’s like Groot. His name is Green Bean and he says Green Bean 1,000 times a day with different inflections.*

Marissa: Even after the birds were no longer in use, canaries held a special place in mining culture.  In his mining memoir, David Coleman, the ‘Eastwood Pitman’, mentions the tradition of keeping canaries at the pit in his book, ‘A Nottinghamshire Pitman’s Story’ writing:

“As a tribute to the canary, every pit top, near the Colliery Manager’s office usually, had an aviary full of canaries. Although they didn’t use them much, they still kept them as a tradition. There was always somebody nominated to look after them. They saved many, many lives.”[11]

Elizabeth: Judging from archival photos, most canaries were taken into coal mines in a simple, open-air cage. So if a canary was exposed to gasses and became unconscious, unless it could be gotten out of the mine super quick it was possible the bird would die. In 1914 a “Resuscitation cage for Mine Canaries,” was touted as a life-saving mechanism for mine canaries. The cage is made of solid metal, with a glass window on three sides so that the canary is visible. A hatch door is located on a fourth side that can be opened or closed. Mesh wire covers the opening of the hatch so that the canary cannot escape. At the top of the cage is a small oxygen tank with a hand pump. If the canary was exposed to a high concentration of toxins in the air and passed out, it could be revived by closing the hatch and pumping oxygen into the sealed cage.[12] This was probably pragmatic as much as it was about caring for the birds however. If you could resuscitate your animal, you wouldn’t have to head to the surface for another one. Nevertheless, miners certainly felt affinity for the animals underground with them.

Canary revival cage with oxygen cylinder as handle circa 1914. The World’s Work. 28. Public Domain.

Marissa: In his study of Colorado mining Killing for Coal, historian Thomas Andrews maintains that “the miner’s canary was usually a mouse” in Colorado mines.[13] According to oral histories, some Colorado mines were filled with small rodents who had at some point hitched a ride into the depths in the oats and hay that were taken down for the mules that would haul the loaded skips out of the mine. One miner fondly remembered his little mice friends saying, “Oh yeah, the little buggers knew their name… Little by little you could just about feed them by hand.”[14] But the mice weren’t just companions for miners, they functioned as sentinels for danger. Mice are also sensitive to carbon monoxide. If a miner noticed the mice acting weird, either scurrying at top speed because it detected a subtle vibration in the mine that humans can’t, or if it was acting lethargic, the miner knew it was time to get out of there.[15]

Elizabeth: The US Bureau of Mines used canaries to test other safety things. In 1923 the Bureau released a study entitled “Carbon Monoxide Hazards from House Heaters Burning Natural Gas.” They were testing a variety of house heaters and the amount of carbon monoxide they could emit in a family home. The study clearly used canaries as one part of the test. For example, one test result states, “No odor of aldehydes. Canary unaffected after 3 minutes exposure.” Another result states, “Strong odor of aldehydes. Canary unable to stand up after 3 minutes exposure.”[16]

Marissa: Now here’s a fun fact that might surprise you. Canaries were actually used in mines in the UK as late as 1996 when legislation officially ordered miners to replace canaries with electronic carbon monoxide sensors, known as “electronic canaries.” The process of phasing out mining canaries had begun in 1987. Miners lamented the replacement, with one saying “There is something about hearing them singing when you start work that lifts the spirits. There’s no doubt that collieries will be less colourful and quieter places without them.”[17] Others worried about the substitution in more practical terms, “batteries can fail – canaries don’t”.[18]

Elizabeth: But even if canaries aren’t keeping coal miners company these days, we still have the good ‘ol “canary in a coal mine” figure of speech. Writing in the Wall Street Journal in 2014, linguist Ben Zimmer caustically wrote that the canary-coal-mine metaphor has seen better days, its health imperiled by overuse. A once lively figure of speech has been deadened into a cliché for any early warning signal…Nowadays the idiom is so well-known that the “coal mine” part can safely be dropped. Environmentalists, for instance, speak of “climate canaries,” natural phenomena that could signal disastrous climate changes in the future. It may be time, however, to let the canary escape its metaphorical cage and fly free from the language.”

Marissa:In the same article, Zimmer gives the earliest instance that “canary in a coal mine” was used as a figure of speech. In 1915, the Herald and News of Newberry, S.C. ran a circular for the Chautauqua circuit. Based out of the Chautauqua Institute of Western New York, lecturers would travel the lyceum circuit across the country giving these talks to the public. This particular 1915 circular stated, “A Chautauqua is to a town what a canary is to a coal mine. If the intellectual and moral atmosphere of this is such that a Chautauqua can’t live in it, then we must change the atmosphere or get out.”[19]

Elizabeth: So there ya go. I did a Google search on “canary in a coal mine” to see how many hits would come up and it was 2,780,000. From a quick skim, it looks like most of those hits were using the phrase figuratively.

Thanks for listening!


[1] Barbara Freese, Coal: A Human History (Penguin Books, 2014) 13.

[2] C.G. Douglas, “John Scott Haldane, 1860-1936,” Obituary Notices of Fellows of the Royal Society, Vol. 2, No. 5 (Dec., 1936), pp. 114-139

[3] Douglas, “John Scott Haldane, 1860-1936.”

[4] “New Use for the Canary.” Nottingham Evening Post, 21 Dec. 1906, p. 4. British Library Newspapers


[5] Burreil G, Seibert F. “Experiments with small animals and carbon monoxide.” Journal Ind Eng Chem.

1914;6(3):24 1-244

[6] Christal Pollock, “The Canary in the Coal Mine,” Journal of Avian Medicine and Surgery,

Vol. 30, No. 4 (2016): 386-391.

[7] Dugald Macintyre, “Bird Life Savers out of Work,” Dundee Courier, Oct. 19, 1923; Amelie Bonney, “Canaries in the Coal Mine,” Gale Ambassadors https://review.gale.com/2020/09/08/canaries-in-the-coal-mine/

[8] Pollock, “The Canary in the Coal Mine.”

[9] George A. Burrell and Frank M. Seibert, “Experiments with Small Animals and Carbon Monoxide,”The Journal of Industrial and Engineering Chemistry, (March, 1914) :241–24.Experiments with Small Animals and Carbon Monoxide | Industrial & Engineering Chemistry (acs.org)

[10] Macintyre, “Bird Life Savers out of Work.”

[11] Coleman, D.   A Nottinghamshire Pitman’s Story, (2017) quoted on David Amos, Mines2Minds, https://miningheritage.co.uk/pit-canaries-end-of-an-era/

[12] “Resuscitation Cage for Mine Canaries,” The World’s Work, (September, 1914): 147. https://archive.org/details/worldswork28gard/page/474/mode/2up

[13] Thomas G. Andrews, Killing for Coal: America’s Deadliest Labor War (Harvard University Press, 2008), 129.

[14] Andrews, Killing for Coal, 130.

[15] Andrews, Killing for Coal, 130.

[16] G.W. Jones, L.B. Berger, and W.F. Holbrook, “Carbon monoxide hazards from house heaters burning natural gas,” Washington, D.C. : U.S. Dept. of the Interior, Bureau of Mines : 1923. https://babel.hathitrust.org/cgi/pt?id=mdp.39015077568106&view=1up&seq=15&skin=2021&q1=canary

[17] “Singing as they go, miners’ little friends head for retirement,” Daily Mail, 2 Jan. 1996, p. 26

Daily Mail Historical Archive https://link.gale.com/apps/doc/EE1860550990/GDCS?u=oxford&sid=GDCS&xid=1f1e2b3a

[18] “Singing as they go, miners’ little friends head for retirement.”

[19] Ben Zimmer, “A Canary, a Coal Mine and a Cliché,Wall Street Journal (Online); New York, N.Y. [New York, N.Y]. 14 Mar 2014.


Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.