China’s air pollution can be so dense that grey plumes are visible from space.
But while smog can cause heart disease, lung cancer and high blood pressure in humans, it seems to make homing pigeons fly faster in one of China’s most hazy regions.
The researchers think the unexpected phenomenon may be down to a scent the birds can use to find their way home.
While smog can cause heart disease, lung cancer and high blood pressure in humans, it seems to make homing pigeons fly faster in one of China’s most hazy regions. A stock image of smog in Shanghai is pictured
Researchers from Nanjing University in China and the University of California, Los Angeles, analysed the performance of racing or ‘homing’ pigeons taking part in races on the North China Plain.
The birds are known for their ability to find their way back home at speeds of around 37mph (60km/h) and were famously used in both World Wars because of their reliability.
The researchers used publicly available data gathered from pigeon racing agencies as well as environmental organisations in the autumns of 2013 and 14 to analyse the speed of the birds in the region, where smog is usually thicker than in other parts of the vast country.
When looking for correlations between the birds’ times and pollution levels, they expected to see a drop in performance.
The researchers used publicly available data from pigeon racing agencies as well as environmental organisations to analyse the speed of the birds. Contrary to their expectations, pigeons homed significantly faster in polluted conditions. These charts show the varying correlations depending on other conditions
WHY DO THE PIGEONS FLY FASTER?
Navigational advantage:
The smell of smog, which is composed of organic particles in China, may help the birds navigate.
‘While air pollution cannot enhance vision, it might enhance olfactory navigation efficiency by providing supplemental olfactory cues to home,’ the study says.
Motivation:
Alternatively, the researchers think the birds dislike the smog and are simply upping their speed to fly out of it as soon as possible.
‘Decreased homing time under air pollution could be explained by an enhanced motivation to home; a possibility proposed several years ago that remains untested,’ they write.
‘Air pollution might be an indication of poor environmental quality, which might trigger rapid escape.’
The birds many want to get out of the smog to avoid predators surprising them in poor visibility too.
‘By homing faster when flying through haze pollution, pigeons reduce the relative amount of time they are exposed to harmful or dangerous situations while away from the safety of their home roosts,’ the study said.
‘We might expect 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,’ the researchers wrote in the study, published in Nature’s Scientific Reports.
They considered variables including race distance, wind direction, speed, weather conditions and air quality.
Temperature was found to have no ‘significant’ effects on homing time, whereas the others either slowed the birds down or helped them get to their destination more swiftly.
The researchers added: ‘Contrary to our expectations, pigeons homed significantly faster when flying through more polluted conditions.’
Using a model, they estimated that pigeons increase their homing speed from 35 mph (55.6km/h) when flying in unpolluted conditions, to 42 mph (68.2km/h) when the pollution index hit a high score of 500.
While they are not exactly sure why smog is responsible for the performance boost, they have a couple of ideas to do with navigation and motivation.
It is generally accepted that pigeons use the sun and geomagnetic field as a compass, and visual and olfactory cues to create a map.
‘Could air pollution enhance pigeon visual and/or olfactory abilities, and by doing so explain the reduced homing time?’ the experts asked in their paper.
Because smog usually reduces visibility, particularly in North China where smoggy particles are the main pollutants, the study suggests that visual cues aren’t as important to the birds’ navigational techniques as expected, so poor visibility didn’t affect their speed.
While the experts are not exactly sure why smog is responsible for the performance boost, they suggest that the birds may fly faster than usual – and not just as efficiently – because of the smell of smog. A stock image of racing pigeons being released is shown
‘This finding is consistent with previous studies that have shown that pigeons are able to home perfectly well from unknown sites where landmarks are unfamiliar, even when flying with frosted lenses that impede vision,’ they write.
To explain why the birds may fly faster than usual – and not just as efficiently – they suggested the racing pigeons may be stimulated by the smell of smog.
‘Olfactory cues have been shown to play an important role in avian navigation, and in pigeons it is probably a fundamental homing mechanism,’ they write.
They think the organic particles that make up the smog – from burning coal and waste – may help the birds navigate by providing stronger markers for the birds to use when finding their way home.
Racing pigeons are known for their ability to find their way back home at speeds of around 37mph (60km/h) and were famously used in both World Wars because of their reliability (pictured)
‘While air pollution cannot enhance vision, it might enhance olfactory navigation efficiency by providing supplemental olfactory cues to home,’ the study continued.
Alternatively, they suggested the birds might dislike the smog and are simply upping their speed to fly out of it and get back home as soon as possible.
‘Decreased homing time under air pollution could be explained by an enhanced motivation to home; a possibility proposed several years ago that remains untested,’ they write.
‘Air pollution might be an indication of poor environmental quality, which might trigger rapid escape.’
The birds many want to get out of the smog to avoid predators surprising them in poor visibility too.
‘By homing faster when flying through haze pollution, pigeons reduce the relative amount of time they are exposed to harmful or dangerous situations while away from the safety of their home roosts,’ the study said.
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