The practice began in the late 19th century. Miners would bring caged canaries with them, as the birds' high metabolisms and small size made them far more sensitive to toxic, odorless gases like carbon monoxide. A distressed or dead bird was the only immediate warning to evacuate. Surprisingly, some miners tried to revive the birds using specially designed cages with self-contained oxygen supplies. This highlighted their dependence and often fondness for the small creatures that shared their per

Derek is at the Minera Lead Mines and Country Park, where lead was processed during the 18th and 19th century. 🚶 Weatherman Walking ▶️ Watch on BBC iPlayer | BBC Cymru Wales