Canaries have historically been used as an early warning system in coal mines to detect the presence of toxic gases, particularly carbon monoxide. Carbon monoxide is a dangerous gas because it is colorless, odorless, and highly toxic, making it difficult for miners to detect with their senses. Canaries, on the other hand, are much more sensitive to the presence of this gas than humans.
When carbon monoxide builds up in the mine, it affects the canary's ability to breathe, and the bird shows signs of distress, such as becoming lethargic or even dying, which serves as a clear signal to miners that the air quality is hazardous. The use of canaries in this way helped save many lives, as miners could evacuate before they were exposed to dangerous levels of the gas. Although the practice of using canaries has been replaced by modern detection equipment, it remains an important part of mining history.