When planting crops in rural areas, in order to prevent sparrows from hurting crops, many people will choose to hang some red cloth or tie some red ribbons on crops, which can protect crops well and sparrows will hide far away when they see them.
Because of the long-term physiological function, sparrows think red is poisonous or dangerous, so they are afraid of it and generally stay away.
Extended data
In order to know how weak or small the stimulus that animals can feel, we can first present a larger visual stimulus of movement: a line, a circle or a light spot for animals to track with their eyes or heads, and then the intensity of this stimulus will gradually decrease and weaken until animals no longer have visual tracking movement.
At this time, the minimum effective stimulus value is the visual threshold, which can be used as an index of animal sensory sensitivity.
For example, let the wolf listen to a high-frequency pure tone, and the wolf will erect its ears and swing towards the sound source. Then increase the pure tone frequency until the wolf's reaction disappears (inaudible). At this time, the frequency of pure tone is the upper limit of the wolf's hearing, which represents the audio limit it can hear. It is found that the pure tone frequency that wolves can hear is much higher than that of humans.
References:
Baidu encyclopedia-animal senses