Pigeons home faster through polluted air

Air pollution, especially haze pollution, has become a global environmental problem and the situation is much more serious in rapidly developing countries, such as China1,2, India3, Mexico4, etc. A large literature has documented deleterious effects of pollution on humans, such as increased incidences of heart disease, lung cancer, and high blood pressure5,6. Based on these risks, public health officials have suggested that people reduce or avoid outdoor activities to protect their health when the air is heavily polluted. However, much less is known about how non-human animals react to air pollution. Due to their higher metabolic rate and special respiratory system, birds should be particularly sensitive to air pollution7,8 and, like in humans, air pollution has been documented to cause serious health problems for birds7,9. For instance, the accumulation of heavy metals and fine particles results in liver and lung damage9,10,11 and may affect flying ability. Moreover, birds’ navigation, which relies in part on visual or olfactory cues12,13, might also be affected by air pollution, because of the reduced visibility or chemical interference under conditions of heavy haze pollution14,15. Homing pigeons are an ideal model system to study the effects of air pollution on bird behaviour. Pigeon navigation mechanisms are well-studied: pigeons use solar and geomagnetic cues as a compass to determine the direction to home, and they use olfactory and visual cues as a map to determine their position in space16,17. Thus, we might expect that pollution would negatively interfere with pigeon navigation and pigeons would both fly more slowly and be less successful at returning to their home roosts when flying through more polluted air. To test this hypothesis, we used a large data set generated by 415 pigeon races on the North China Plain, an area with China’s worst air pollution, to evaluate the effects of air pollution on pigeons’ homing performance.