Friday, 2 December 2011

Part 5: Down the mines

Border canary
The canary in the coal mine is a familiar expression today, generally used either for some environmental change or for some ominous economic event, but how did it originate? And for that matter, what were canaries doing down the mines in the first place?

The story starts a long, in fact very long, time ago, with the evolution of the first dinosaurian ancestors of birds during the Triassic. Life on earth was still recovering from the greatest mass extinction event ever, the end-Permian event, when perhaps 95% of all the species of living things on earth died out. The survivors at first had little competition, but as new species evolved the evolutionary arms race intensified.

One of the areas of competition was in physiology. Active animals with a high metabolic rate could be up and about, finding food and catching prey, while less energetic animals were unable to escape or compete. To run an active metabolism however, an animal needs to be able to absorb oxygen efficiently from the air, and two methods eventually dominated.

The mammals evolved a muscular sheet, the diaphragm, inside their body cavities. This worked with the muscles of the thorax to improve the pumping of air in and out of the lungs, which themselves became more complex. The ancestors of dinosaurs used a different method. Air sacs extended from the lungs, at first only a few, but eventually more and more. These air sacs received air on inhalation, and on exhalation the air passed through thin tubes, the parabronchi, on its way out of the body.

Bird lungs - inhalation above, exhalation below
By the time birds evolved the system had become complex and highly efficient, with the air in the exchange surfaces being almost completely changed with each breathing cycle, while mammals changed only a small percentage. The result was that birds are far more efficient at absorbing oxygen from the air than mammals are. This is why geese for example can fly right over the top of Mount Everest, while the mountain climbers far below have to use supplementary oxygen tanks to survive.

The efficient avian lungs however have one drawback. They do not just absorb oxygen from the air, but inevitable accelerate the absorption of other gases. As a result, birds are highly susceptible to toxic gases. In many cases of the unexplained death of a pet bird, toxic fumes, often from an overheated non-stick pan, are the actual cause.

How birds came to be used as living gas detectors is down to one of the most famous scientists of the 19th Century, JS Haldane. A brilliant investigator, and dedicated Socialist, he devoted a great deal of time to the benefit of working men, especially miners. As part of his investigations of mining disasters and their causes, he analysed the various gases (mainly methane and carbon monoxide) which were so lethal , especially in coal mines. After experimenting on mice and birds, he suggested that each mine should have some canaries on hand in case of trouble. A canary could be taken down to the suspected trouble spot and if it showed signs of distress the miners would know to get out and improve the ventilation in a hurry. The scheme caught on, and even after mechanical devices began to take over, canaries were still kept on hand in case of emergencies.

With their lives depending on their birds, it is unsurprising that even today mining areas are strongholds of canary keeping g in the UK. For a round up of some of the clubs, shows, and other features of modern canary keeping, I will finish of this series of posts next week.

(images from wikipedia, sciencephoto, petinfospot)

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