Dean Barr had more than 10kg of carbofuran in his possession, enough 'to kill every bird of prey in Scotland six times over'

A gamekeeper at an exclusive Highland resort has admitted storing the largest amount seized to date of a banned pesticide widely used to kill birds of prey.

Dean Barr, the sporting manager at Skibo estate near Inverness, was fined £3,300 at Inverness sheriff court after he admitted possessing more than 10kg of the pesticide carbofuran: enough, said conservationists and the police, to kill six times Scotland's bird of prey population. The resort is known for having hosted the wedding reception of Madonna and Guy Ritchie.

Barr was arrested in a police raid in May last year after a group of hill walkers found a dead golden eagle on the Skibo estate, part of the Skibo Castle resort owned by the US investment banker Ellis Short, overlooking the Dornoch Firth.

Another dead golden eagle had been found several days earlier. Both incidents led to a police raid, when a third dead golden eagle, a dead buzzard and a dead sparrowhawk – all protected species – were found on the estate.

Laboratory tests confirmed three birds were killed by carbofuran, a pesticide banned in the UK in 2001 that attacks the nervous system, causing paralysis and seizures. A few granules can be lethal.

One of the three eagles was killed with another chemical, aldicarb. While no poison was found in the buzzard, the police also found a red grouse heavily dosed with carbofuran that appeared to have been staked out as bait.

It is one of the largest single incidents of bird of prey poisoning detected by the police in Scotland, but no one has been charged or convicted in connection with these alleged offences. Barr was charged with possessing the carbofuran, which was found locked in a store to which he had the key.

His defence lawyer, David McKie, told the court that Barr was guilty only of a "foolish omission". He had never used the chemical but had brought it to Skibo from his previous estate, where it was legally used on the farm, because he did not know how to dispose of it.

Sheriff Margaret Neilson said this explanation was "extraordinary" and that if Barr had been found guilty of poisoning the birds he would have been jailed.

Stuart Housden, the director of the Royal Society for the Protection of Birds Scotland, which took part in the police raids, said: "If ever there were a more compelling reason for an individual to feel the full weight of the law in a wildlife crime case, then the conviction of Dean Barr was it.

"Carbofuran is a deadly and illegal substance, regularly used as a poison by those who wish harm to birds of prey in Scotland. Barr, a man who is a professional sporting manager with years of experience, was found with an unprecedented amount of this banned chemical in his possession. We are pleased that the Sheriff has sent out a clear message that society will not tolerate such reckless and deplorable behaviour in the countryside."

Chief inspector Matthew Reiss, Northern Constabulary's wildlife crime co-ordinator, said: "Experts say that the amount of poison our officers uncovered would have been enough to kill every bird of prey in the UK.

"The poison was discovered within premises operated and solely accessed by Mr Barr on Skibo estate land. It was found in the course of an investigation launched after the discovery of dead birds of prey, believed to have been illegally killed on the estate, including three golden eagles and a sparrowhawk and a grouse laced with Carbofuran, which was pinned to the ground by a metal spike. Undoubtedly this was a prepared piece of bait.

"Our investigation into the deaths of these birds remains open. There is no excuse for the illegal killing of some of our most iconic species."

A spokesman for Skibo said the estate had no comment to make about Barr's conviction. After the discovery of the dead birds last May it had said: "The owners and management of Skibo Castle are committed conservationists and do everything they can to support the welfare of wildlife and birds. We will co-operate fully with the authorities in their investigation."

In an unrelated case, another gamekeeper in the Highlands pleaded guilty to having a dead red kite in his vehicle. James Rolfe, based on the Moy estate near Inverness, was fined £1,500.