A rubber band has been seen around the head of a duck and RSPCA inspectors are trying to find the bird to free it.
They also want to discover if the band was dropped by a postman. The mallard duck was discovered next to a stream in King's Lynn, Norfolk.
Inspectors fear the problem might stop the duck eating and will try to catch it and remove the band.
"Bands, of the type used for bundles of mail, were discovered near where the duck was found," said a spokeswoman.
"We have spoken to the Post Office about it. But we can't be sure whether it was dropped by a postman.
"We will be monitoring the situation as her condition may deteriorate with the rubber band in her beak.
"People really need to be more careful about picking up their litter as it can pose a danger to all sorts of wild and domestic animals."
The Royal Mail switched to red rubber for the bands it uses around post bundles 18 months ago to make them easier for postmen to spot and pick up when dropped.