Snakes on the brain: songbirds imagine sticks are serpents
A bird with a hatred of snakes has an over-active imagination that can turn a harmless stick into a deadly serpent.
When the Japanese tit hears a rattling alarm call, it cannot help but think of snakes, a study has found.
In just the same way, a snake-phobic human will have only one thing in mind if he or she hears someone shout: “Snake!”
The ability to visualise a specific mental image in response to a vocal sound was once thought to be unique to humans.
Scientists used an inanimate wooden stick to demonstrate the same talent in the Japanese tit, a songbird that produces particular alarm calls only when it encounters dangerous snakes.
In a series of experiments, recordings of snake-specific calls were played while the birds approached a stick being moved in a serpentine fashion up a tree trunk or along the ground.
The birds responded as if threatened, but ignored the stick if other calls were played or the stick’s movement was not snake-like enough.
Lead scientist Dr Toshitaka Suzuki, from the Centre for Ecological Research at Kyoto University, Japan, said: “These birds do not respond to the calls in a uniform way, but appear to retrieve a snake image and then decide how to deal with the predator according to the circumstance.
“With a snake’s image in mind, tits can efficiently search out a snake regardless of its spatial position.”
When they meet a real snake, Japanese tits typically go on the offensive, hovering over the reptile while spreading their wings and tail to deter it from attacking.
Faced with a snake-like moving stick, the birds reacted in the same way but their distraction behaviour was more limited.
“They may have realised that the stick was not a real snake once they got close enough,” said Dr Suzuki.
Many animals, including monkeys and meerkats, have been shown to produce calls that warn of specific predators or share the discovery of particular kinds of food.
Dr Suzuki added: “Retrieval of mental images may also be involved in other animal communication systems.
“Uncovering cognitive mechanisms for communication in wild animals can give insights into the origins and evolution of human speech.”
The research appears in the journal Proceedings of the National Academy of Sciences.