Pollution-tracking by bird.

Nature reveals the outdoor version of canaries in a coalmine – how researchers use swallows and homing pigeons to track pollution:

Nesting birds that feed on insects that hatch in lake or stream-bed sediments may make good biomonitors for pollution, says Thomas Custer of the US Geological Survey’s Upper Midwest Environmental Sciences Center in La Crosse, Wisconsin. That’s because any contamination in the sediment will make its way into the birds and into their eggs and young.

Swallows are not the only birds being used for such purposes. Richard Halbrook, a wildlife toxicologist at Southern Illinois University in Carbondale, uses homing pigeons to monitor air quality.

Homing pigeons — once used to carry messages over long distances — are still bred by hobbyists around the world, who use them for competitions. Many birds are kept in lofts, and often in cities, so breathe ambient air. Even better, their life histories are well known, which is not possible for wild birds. Pigeon hobbyists “keep pretty elaborate records”, Halbrook says.

In a pilot study involving birds purchased from hobbyists in China, the Philippines and the United States, Halbrook found stunning health-related differences that were apparently related to air quality. In Beijing and Manilla, for example, he found black lungs and enlarged testes. In one case, a testicle was so huge it was one-fifth the weight of the entire bird. But in less polluted cities elsewhere in China and in the United States, the birds’ organs were much healthier.

The thing with swallows and homing pigeons is that they keep coming back to the same nests. Think of them as occupying a specimen cage that’s as long as a continent….