A mystery surrounding the repeated appearance of road cones in the middle of the road at Homer Tunnel over the past several weeks as been solved by CCTV.

The location of the road cones had baffled the Milford Road Alliance for several weeks.

Workers kept arriving to find the road cones in "odd places", but once they reviewed the footage the culprits were caught.

Milford Road Alliance manager Kevin Thompson told Newshub he thought kea were using their keen ears and quick-thinking to their advantage.

"We think the kea listen for the cars in the tunnel and move the road cones between the streams of traffic."

He suggested it could even be an attempt to get cars to slow down or to stop and feed them.

In response to the inventive birds, the Milford Road Alliance - a partnership between NZTA and Downer NZ - was looking at heavier road cones.

It discourages people from feeding the birds.