When methane built up, or carbon dioxide built up, or oxygen was diminished, the birds would swoon before people would -- so it acted as an early warning system: Hey, get out of the mine. Things aren't going so well.
Când creştea concentraţia de metan sau CO2, când scadea cantitatea de oxigen, păsările începeau să se agite, înainte de oameni -- ca un sistem de avertizare: „Afară din mină! Nu-i a bună!”