Does red enrage bulls?

There are those folks who still believe that a red rag literally drives a bull into a fury. Then there are those hip young things who read the internet and know that’s impossible because bulls are colour-blind. The truth lies somewhere in the middle: red doesn’t make bulls angry, but they are not colour-blind, either.

Mind you, they don’t see the world quite as we do. Colour vision relies on light-detecting cells in the back of the eye called cones, and the cones come in different flavours depending on which part of the visible spectrum they respond to most. Humans have three kinds which respond most strongly to yellow, green and blue light. We perceive other colours by comparing the signals from these detectors against one another. So if the yellow cones are strongly stimulated but the green ones are weakly stimulated, we perceive red.

Cattle have only two kinds of cones, sensitive to blue and green light. This doesn’t stop them perceiving red, though. Remember that we don’t have detectors for red either, the perception of red being inferred from the pattern of stimulation among the cones. Cattle can do something similar to tell red from other colours.

Okay, so bulls know red when they see it. But it doesn’t send them into a fury. It seems it can affect their behaviour, though, with at least one study showing that calves are more active in red light than blue light. Not angry, just active.

The bull-fighter’s red cape probably attracts the bull’s attention because it is moving, but the colour may contribute in some way to the bull’s behaviour. As for the anger — that probably has less to do with the colour or the movement and rather more to do with being taunted and provoked by the jumpy fellow in the wacky get-up.

Bulls can see red, even if they don’t necessarily see red when they see red — if you see what I mean. And that’s no bull.

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