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"With a budget of just $1500 (£990), Dr Anderson said the initial plan was to modify an existing motor from a remote-controlled aeroplane or car but they were all too large to fit inside the 18 gram bird, the size of an average house sparrow.

"Our engineer built a linear motor from first principles, and then re-miniaturised it until we got something to fit."

Once the motor was in place and the robot chip was programmed, the mounted bird was put in the wild along with a discreet sound system playing swamp sparrow calls to attract others.

The wing-waving robot lasted for two months but was regularly attacked, said Dr Anderson.

"We had no back up - every day was a wish and a prayer that he survived the sixty trials," she added.

"Eventually the head fell off and the wing stopped moving."
Male aggression

The living male birds were equally aggressive to Robosparrow whether its wing movements were activated or not, the researchers found.

"It confirmed our hypothesis that the wing-waving behaviour is functioning male aggressive communication," said Dr Anderson.

"It was a lot of work - the engineering students had never done it before, the taxidermist we used had never done it before.

"We really just scratched the surface of what this behaviour is.""