The Department of Conservation (Doc) has picked up the carcasses of 10 morepork and two kea which had been killed by vehicles on the Milford Highway.
Doc scientist Moira Pryde, of Christchurch, said morepork were particularly vulnerable to traffic, as they perched near the road at night, seeking potential prey and often flew up into the headlights of cars.
"This is the highest number of morepork deaths caused by vehicles in Fiordland National Park since I started work here 15 years ago," Ms Pryde said.
Research into morepork breeding, which began in 2008, showed breeding could be erratic.
This season had been identified as the best in four years.
Most monitored female morepork had raised two chicks.
In the previous three breeding seasons no chicks were known to have survived.
"The 13 chicks produced this year will be a boost to the population who have suffered poor breeding years and road-related deaths."
The increase in breeding had been put down to a good food source in the form of mice, due to last year's heavy beech tree mast. Morepork can eat as many as five mice a night.
Kea were also falling victim to vehicles. Two juveniles were killed by vehicles near Monkey Creek in December.
"Kea are most vulnerable near car parking areas along the alpine section of the road, where some tourists, including tour buses, feed the kea, encouraging them to hang around on the roadside, in the way of traffic."
Doc reminded visitors that kea must not be fed and drivers need to take extra care around the Monkey Creek.
"Speed is definitely a factor contributing to the deaths of native birds along the Milford Road and staff based in the area say there have been several reported near-misses."
The public are asked to report any dead native birds to the Doc Te Anau Area Office.
