You occasionally see what look like large nests on Birch trees but on closer examination you discover that they are not in fact nests at all but bunches of stem,leaf or root material growing from one or more points on the tree.In the case of the Birch,the growth distortion is caused by a fungus.They don't harm the tree which continues to grow as normal.Some trees could have a dozen or more growths .The tree in the picture I found on the way up to climb Moylussa in the Slieve Bernagh mountains in east Clare.
