And what they found was parrots messing with the cones in an attempt to cause traffic accidents and kill humans. Okay, maybe that last part is just my take on the situation, but they definitely did see birds moving the cones around.
The answer? The Transport Agency is going with heavier cones. Killing the birds in an effort to keep them from killing off humanity is not an issue as this species of parrots, called Kea, are endangered.
Only around 5,000 of them remain.