Two young kea have died after suspected car surfing at Deaths Corner in the Otira Gorge.
The Department of Conservation said both birds suffered head injuries from similar incidents in the past week.
Senior ranger Chris Stewart, from DoC's Arthur's Pass team, said the parrots were known for landing on cars and picking things off, but sometimes when the cars took off the birds stayed put.
"When the car gets going, they are really in trouble," Mr Stewart said.
It was not the first time kea had been seen car surfing in the area, however an unusually high number of birds had been congregating at the Otira Viaduct lookout this year, he said.
Members of the public had reported seeing the birds on moving cars, and then trying to fly away.
"They are 1-year-old, teenagers, still having fun."
They also seemed to copy each other.
"[Car surfing's] a bit of a problem."
There was little DoC could do about it, other than educate people to not encourage the birds around people and their cars, Mr Stewart said.
The Kea Conservation Trust said some of the inexperienced birds were not gaining height as they attempted to fly off the moving vehicles.
It asked motorists to slow down until they were sure kea were not attached to the car roof.
- The Greymouth Star