As the vital hatching season begins, volunteers across the Highlands are keeping watch over nests 24 hours a day. RSPB officials fear the latest robberies could herald a spate of attacks by egg collectors.
Forty years after it returned to colonise Scotland, the fish-eating bird of prey has become a victim of its own success. There are now so many nests in Perthshire and Tayside, built after the birds return from Africa each summer, that the RSPB cannot monitor them all.
The latest attacks, which began last week, were on unprotected eyries. A gang of thieves used tree irons to climb 60ft Scots pine trees in Perthshire and Strathspey to reach the nests. Nine eggs were removed.
After the attacks, RSPB officials appealed to ornithologists to take to the hills to prevent further losses. Most sites are now guarded all day and volunteers have begun to cover tree trunks with razor wire and cut down branches to deter raiders. David Mitchell, the RSPB's Scottish representative, said: "The response has been terrific. Volunteers are out there giving up their time to help protect one of world's most magnificent hawks."
Egg collecting, which is illegal, has been fashionable since Victorian times. Today, most gangs are found in Yorkshire and the Midlands. Gang members steal eggs and inject solvents which "dissolve" the embryo before the egg is dried and polished.
As recently as 1991, up to half of all osprey eggs in Scotland were stolen. The number of attacks declined, however, after a series of high-profile prosecutions in which raiders were fined more than pounds 10,000. But in the past two years the number of attacks has begun to rise.
The trend worries and angers the RSPB. Mr Mitchell said: "Not only is it illegal, but it is immoral. The chicks die an agonising death - literally dissolving. It means there are fewer adults each year and people across Britain are denied the opportunity to see one of the most thrilling natural sights - an osprey swooping down on to a loch to seize a trout. These people must be stopped."
The latest raids have prompted some RSPB members to call for a change in the law to force persistent offenders to report to police stations during the osprey breeding season. Keith Brockie, a wildlife artist who helps to safeguard eyries in Perthshire, said: "Most of those who raid nests keep on doing so even if they are fined in the courts. Few collectors can kick their nasty habit. We have to protect the birds from these people and if they are, say, in England, they should be required to report to police each day in April and May to stop them heading north."
In recent years the successful reintroduction of the osprey north of the border has raised hopes that it will recolonise England, where it has been extinct for many years The RSPB insists that the latest attacks threaten the process.
Mr Mitchell said: "After the low point of 1991 we thought we had conquered the problem of egg thefts and the bird looked set to head south. It was wiped out in Britain in the early part of this century by hunters and egg collectors. We must not allow it to happen again."
Tayside Police are investigating last week's incidents.