Nowadays, we see canaries as colorful birds who sing beautiful songs and make a great pet. But for most of the 20th century, canaries were heroes responsible for saving the lives of coal miners. This is where the popular phrase “canary in the coal mine”, used to describe an indication of an upcoming danger, actually comes from.
Coal miners face a number of dangers when they enter a mine, ranging from explosions and cave-ins to being exposed to poisonous gases like carbon monoxide. The latter is especially dangerous as it is impossible to detect using human senses. Being odorless and colorless, the gas can cause poisoning and become fatal without coal miners even noticing something is wrong until it’s too late.
Canaries are even more susceptible to the effects of carbon monoxide than humans. Due to their rapid breathing, the gas spreads rapidly through their small bodies, and they show signs of poisoning fast. As a result, famous physician and psychologist John Scott Haldan recommended that coal miners carry canaries with them when they enter Earth.
If the canaries remain well and chirping, there is no carbon monoxide in the air. But if they faint, it is a sign coal miners are surrounded by poisonous gas, and they could evacuate to safety before the poisoning becomes fatal for them.
Canaries started being coal miners’ companions in 1896 in Great Britain before the coal miners in the United States and Canada followed the example. Many coal miners appreciated the canaries and treated them as pets. Special cages with oxygen tanks were developed so that canaries could be revived once they fainted.
The practice of using canaries in coal mines was kept until 1986 when the British government forced coal mines to retire canaries in favor of modern tools for detecting the presence of carbon monoxide.