Old, small nest

Old, small nest

Observation - Old, small nest - UK and Ireland. Description: Found this nest at eye level next to Plym Estuary and main road. Tree was on an embankment so was clearly visible at eye level. Obviously an old nest and was very small. Any idea what bird would have constructed this?

Found this nest at eye level next to Plym Estuary and main road. Tree was on an embankment so was clearly visible at eye level. Obviously an old nest and was very small. Any idea what bird would have constructed this?