I don't know if there is a collective noun for a gathering of scarecrows but if there isn't let me suggest a "fright". However, it's only farm scarecrows that seem designed to actually deter birds: most of the others are usually of a much friendlier demeanour, so perhaps that isn't an apt word. This collection of twenty four scarecrows on an allotment in Ross on Wye all looked pretty friendly and were, I think, made for fun rather than deterrence.
photo © T. Boughen Camera: Sony DSC-RX100
