Unexpected sight

Recently with a few hours to fill I took the tube out from central London to Richmond Park which is turns out is the end of one branch of the District line tube. Walking around I thought there was a bright green notice pinned to a tree, as I got closer it moved off and that's when I realised the trees were full of these Ring-necked Parakeets. The estimate in numbers for the Parakeet population across London is near to 6,000 individuals.