Animal lovers are being asked to spot tagged hedgehogs to help experts learn more about the prickly friends.
Hogs which have been rescued by the RSPCA in East Winch, Norfolk, and released into the wild have been tagged so their progress can be monitored.
They've had numbers glued onto their backs which can be seen when the hogs are curled up.
The RSPCA is asking people in East Winch to send details of which hog they spot and where it was.
"It is vital that East Winch Wildlife Centre can find out whether these re-released hedgehogs can survive in the wild and how they learn to fend for themselves after spending time in the centre," an RSPCA spokesman said.
"Staff can then monitor how effective the re-release programme is and make sure that hedgehogs have the ability to look after themselves in the wild."
The hedgehogs are not hurt at all when they are tagged, the spokesman stressed.