The common house sparrow, once seen everywhere in large numbers in Mumbai has become scarce in many areas, and this is causing concern not only to bird lovers but also to scientists.
Formerly, miners used to carry canaries down into the mines with them. If the canaries showed signs of distress it indicated that there were poisonous gases in the air, and the miners would immediately leave the mine. Today, if the sparrows of Mumbai are in distress it could be a warning to human residents. The declining bird population could mean that air pollution levels in the metropolis are rising dangerously; or, since sparrows are grain eaters, it could indicate that the grains that the people are consuming contain higher dosages of pesticides than before.