How birds are used to monitor pollution

From Nature:

Common nesting birds may provide a convenient way to track environmental clean-up efforts. 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. An example, says Custer, is the tree swallow (Tachycineta bicolor), which still showed “significant quantities” of toxic chemicals called polychlorinated biphenols in its eggs and chicks seven years after remediation efforts started at a former capacitor-manufacturing plant in Crab Orchard National Wildlife Refuge in southern Illinois¹. The findings “prompted further sediment removal”, he says.

…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. Plus, the lungs and livers from the birds from Beijing contained three or four times more polycyclic aromatic hydrocarbons, common by-products of fossil-fuel burning, than did those from areas with better air quality. “This suggests that other species, including humans, may also have adverse effects” from these environmental contaminants, he says.