The Avebury Hedgehogs

Yesterday, I went for a long walk around Avebury in Wiltshire, taking in the now legendary standing stones, the long barrow at West Kennett, and Silbury Hill. My friend promised me that we'd see hedgehogs. However, I didn't realise that he meant these:
To the northeast of the village of Avebury are a series of barrows or tumuli surmounted with beech trees. These are known locally as "hedgehogs".

You can appreciate that the shape isn't unlike that of our spiny little friends.