Following a deadly explosion in a Welsh coal mine in 1896, an engineer called John Haldane invented a type of bird cage that allowed canaries to accompany miners into the depths. The small songbirds are much more sensitive than humans to the deadly carbon monoxide gas found underground.
A sudden halt to their singing would warn workers to evacuate the pit – and rescue the canary by closing its cage door and opening a valve to pump oxygen inside. Remarkably, it was only in 1986 that canaries were relieved of their duties detecting noxious gases in UK coal mines.
