A miner holding a canary in a birdcage, 16th February 1970. Used to warn miners of dangerous gases, the birds are now kept in a perspex cage with an oxygen cylinder so they can be revived later. (Photo by David Cairns/Daily Express/Getty Images)
A miner holding a canary in a birdcage, 16th February 1970. Used to warn miners of dangerous gases, the birds are now kept in a perspex cage with an oxygen cylinder so they can be revived later. (Photo by David Cairns/Daily Express/Getty Images)