cluster of snails on tree

cluster of snails on tree

Observation - cluster of snails on tree. Description: A group of snails all clusted about 1.5m up a deciduous tree (sorry, picture is on it's side!). This tree was on the edge of little patch of woodland on a hill overlooking the coast at Brancaster, Norfolk. The hill sloping down was open arable farmland, i

A group of snails all clusted about 1.5m up a deciduous tree (sorry, picture is on it's side!). This tree was on the edge of little patch of woodland on a hill overlooking the coast at Brancaster, Norfolk. The hill sloping down was open arable farmland, it sloped down to the nearby village then the sea a few hundred metres away. The little copse of woodland looked to be old chalk pits or iron workings or something like that.

Why were all these snails clustered together up a tree? They were on the side facing out of the woodland so any birds flying past could see them, it doesn't seem like it would be a good place to hide from birds. Any ideas of what they are or why they do this?