Living in cities exposes people to all sorts of chemical pollutants. Many are harmful even at low concentrations. But it is hard to know what the risks and consequences might be.
The animals we share our cities with can indicate potential sources and effects of such pollution. In this way, they act as sentinels — just like the canary in the coalmine, used to alert underground miners to the presence of dangerous levels of toxic gases in the 19th century.
