Just outside Moana Pool there is a row of silver birch trees, some of which have extraordinary growths on them. As I was taking these photos some passers-by wondered if they were bird's nests, no I patiently explained they were not, they were growths called witches brooms - a type of gall.
It's the tree's response to infection by a fungus - in the UK the commonest species is Taphrina betulina - and it's possibly the same one here. Apparently the infection is passed from tree to tree by a gall-fly. The name stems from the superstition that they were caused when witches flew over the tree.
