Hen harriers have been virtually wiped out by sporting estates across northeast Scotland, according to a new scientific study.

The number of breeding pairs in the Cairngorms National Park, Aberdeenshire and East Moray has plummeted from 28 in the 1990s to just one in 2014 because of “illegal persecution and grouse management practices”, nine experts from the Northeast Scotland Raptor Study Group have concluded.

Their conclusions are backed by wildlife campaigners, who are demanding tougher action by Scottish ministers to crack down on offending landowners. But the study has been attacked by a landowning group as a selective attempt “to besmirch grouse moor management.”

The study, published in the journal British Birds, identified 118 possible breeding areas for hen harriers in northeast Scotland. “The vast majority were on moorland managed for red grouse sport shooting,” it said.

“Peak numbers of at least 28 breeding pairs in the 1990s declined steadily to just three pairs in 2010–12, five in 2013 and one in 2014. Illegal persecution and grouse-management practices are believed to be the main causes of that decline, which occurred despite ample suitable habitat and prey.”

The authors pointed out that two projects to help harriers recover had failed, and a proposed legal protection area had stalled. “Levels of trust and cooperation between most raptor enthusiasts and grouse moor estates in northeast Scotland are at an all-time low,” they said.

“This is one of the most controversial conservation issues in the UK, and we suggest that Scottish Natural Heritage and Police Scotland are best placed to lead on overseeing a recovery plan for northeast Scotland.”

The Royal Society for the Protection of Birds in Scotland highlighted five incidents since 2000 in which hen harriers in the northeast had been shot. “It is depressing that in 21st century Scotland, in areas where intensive management for driven grouse shooting is the main land use, there still seems to be a complete disregard for the laws protecting our birds of prey,” said the society’s head of investigations, Ian Thomson.

“It is disappointing that efforts to tackle raptor persecution are undermined by some representatives of the land management sector, with continued efforts made to downplay the scale of the problem.”

Thomson argued that self-regulation by landowners had failed. “We are calling for the Scottish Government to introduce a robust system of licensing of game bird hunting, similar to systems in place in other European countries,” he said.

But according to Tim Baynes, director of Scottish Land and Estates’ moorland group representing landowners, there were “serious problems” with the new study. “There has been very little harrier surveying conducted recently in the area, with only four per cent of harrier breeding areas covered in 2014,” he said.

Cameras installed at harrier nests on five grouse moors across Scotland in 2015 showed that breeding failures were caused by foxes or bad weather and were “nothing to do with human disturbance”, Baynes said.

“Sadly, this seems to be another instance where raptor study groups have made little or no attempt to engage with land managers who could have helped their research. Even once data is produced, it is often incomplete or only selectively shared in an attempt to besmirch grouse moor management.”

The Scottish Government said it was aware of the new study. “Hen harriers are doing well in the west of Scotland and in Orkney but their absence from some areas of Scotland is a cause for concern,” said a government spokeswoman.

“We have said that we will take further action to regulate game shooting if we judge that to be necessary. We have initiated a study to look at how game bird shooting and management is regulated in other European countries.”