Posted by David Gentry
It is well known that animals and other living things can be used to detect a problem before people become aware of it. These are called sentinel animals or indicator species. A dog barking at noises that people cannot hear is an obvious example. More interesting are certain species in a marine environment that are sensitive to low levels of pollution. For more than a century canaries were used in coal mines to detect toxic gases. They became sick before people became sick, and thus gave miners a chance to escape.
To be effective, indicator species must be sensitive to known dangers. They are used to easily, cheaply and accurately monitor the presence of that danger. It is plain to see if the canary is active and happily chirping or not. A reliable relationship must exist between the state of the canary and toxic gases.
But there are limits to what canaries can tell miners. Dead canaries won’t tell where the gas is coming from or even the specific toxic gas (canaries are sensitive to multiple gases injurious to humans, such as methane and carbon monoxide). Once the canary falls off its perch, the miners know they are facing a hazard but must investigate further to find the source, exact nature and severity of the problem, and then decide what to do about it.