Canaries were once regularly used in coal mining as an early warning system. Toxic gases such as carbon monoxide and methane in the mine would kill the bird before affecting the miners. Because canaries tend to sing much of the time, they provided both a visual and audible cue in this respect. The use of so called miner's canaries in British mines was phased out in 1987.
Matt: CORRECT
Record: 241-194
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