This police handout shows the offending speedster – a duck, and possibly a repeat offender – at 52km/h in a 30km/h zone. /Polizei Inspektorat, Council of Koniz handout/AFP

A radar image of a speed offender caught in central Switzerland revealed that the culprit was not only a duck, but likely a repeat offender, local authorities said.

Police in the town of Koniz, near the capital Bern, were astounded when they went through radar images to discover that a mallard was among those caught in the speed trap, the municipality said on its Facebook page.

The duck was caught going 52 kilometers per hour in a 30km/h zone, the post said. 

The story got even stranger when it turned out that a similar-looking duck was captured flying in the same spot at exactly the same speed, on exactly the same date seven years earlier, the Facebook post said.

The municipality said it had considered whether the whole thing might not be a belated April Fool's joke or a "fake" picture. But the police inspectorate said it was impossible to doctor images or manipulate the radar system.

The computers are calibrated and tested each year by Switzerland's Federal Institute of Metrology (METAS), and the photos taken are sealed, the municipality explained.