 However, the first mentions of the phenomenon came in 1940 by the two Dutch researchers Nikolaas Tinbergen and Adriaan Kortlandt.Tinbergen in 1952 noted, for example, that 'two skylarks engaged in furious combat [may] suddenly peck at the ground as if they were feeding', or birds on the point of mating may suddenly begin to preen themselves.Tinbergen adopted the term 'displacement activities' because the behaviour appeared to be displaced from one behavioural system into another.