​London, March 19 (IANS) Researchers have found that the blue tit, collared flycatcher and pied flycatcher have the fastest eyesight in the animal kingdom, with their vision being more than twice as fast as humans.

Thought to be the fastest of any vertebrate animal, their remarkable vision system, allows them to see the world around them in slow motion.

“Bird species similar to the blue tit, collared flycatcher and pied flycatcher, both ecologically and physiologically, probably also share the faculty of superfast vision,” said lead researcher Anders Ödeen, lecturer at Uppsala University in Sweden.

The study, published in the journal PLOS ONE, showed that perching birds, or passerines, have eyes with a temporal visual resolution -- precision of a measurement with respect to time -- of up to 146Hz.

It is at least 50Hz faster than any other vertebrate, and well over twice as fast as the 60Hz a human eye can detect, the researchers pointed out adding that this indicates an evolutionary history of natural selection for fast vision in these bird species. 

That the small airborne birds need to detect and track objects whose image moves very swiftly across the retina to be able to see and avoid all branches when they take cover from predators by flying straight into bushes, gives an explanation for their fast vision. 

The findings raise concerns about the welfare of small caged birds, especially those kept in areas with modern low-energy or flickering lighting light, which can cause stress, behavioural disturbances and various forms of discomfort in humans and birds alike.

Yet it appears perching birds may have traded their ultra-sharp vision at the expense of sharpness.

While the record for the sharpest vision still rests with eagles, which can detect finer details than any other animal, perching birds can only see in low resolution.

For the study, the team trained wild-caught birds to receive a food reward by distinguishing between a pair of lamps, one flickering and one shining a constant light. 

Temporal resolution was then determined by increasing the flicker rate to a threshold at which the birds could no longer tell the lamps apart. 

These birds are increasingly often kept in rooms lit with low-energy light bulbs, fluorescent lamps or LED lighting. Many of these flicker at 100 Hz, which is invisible to humans but perhaps not to small birds in captivity.