It takes a lot of effort to fly, and bird lungs are therefore more efficient than the bellows arrangements that we share with other mammals and reptiles. The coalminer’s canary and the bird deaths in Rachel Carson’s Silent Spring show their vulnerability to pollution. In Spain, blood tests show that a poor urban diet is leaving house sparrows struggling to cope with modern air pollution, especially in the breeding season. Previously, pigeons in Milan displayed the effects of breathing exhaust from leaded petrol. Ominously, analysis of their droppings shows that Milan’s birds are still being affected by polluted air.