Hawk/goose effect

In ethology and cognitive ethology, the hawk/goose effect refers to a behavior observed in some young birds when another bird flies above them: if the flying bird is a goose, the young birds show no reaction, but if the flying bird is a hawk, the young birds either become more agitated or cower to reduce the danger. The observation that short-necked and long-tailed birds flying overhead caused alarm was noted by Oskar Heinroth. Friedrich Goethe conducted experiments with silhouettes to examine alarm reactions in 1937 and a more systematic study was conducted in the same year by Konrad Lorenz and Nikolaas Tinbergen which is considered one of the classic experiments of ethology.

As part of their introducing experimentalism into animal behavior research they performed experiments in which they made 2-dimensional silhouettes of various bird-like shapes and moved them across the young birds' line of vision. Goose-like shapes were ignored while hawk-like shapes produced the response. Later Tinbergen reported that a single shape that was sort of an abstract composite of the hawk and goose silhouettes could produce the effect if moved in one direction but not the other. A study later confirmed that perception of an object was influenced by the direction of motion because the object in question was considered to be moving forwards in that direction. Initially thought to be an inborn instinct developed from natural selection, it was subsequently shown by others to be socially reinforced by other birds.