An anonymous donor was so concerned by the news of one of the worst episodes of persecution in modern times, that they have matched the £5,000 being offered by RSPB Scotland.
The money will be paid for information which leads to the successful conviction of those who killed four buz-zards and 12 red kites.
The birds were found dead within two square miles south east of Conon Bridge near Dingwall. It is understood at least six have been confirmed poisoned, and further tests are continuing.
The poisoning of red kites has been associated with land managed for driven grouse shooting in the past, but there are no grouse moors in the immediate area of where the birds were. It is predominantly farm land with areas of woodland.
Douglas McAdam, chief executive of the landowners' organisation Scottish Land & Estates (SL&E), said: "We encourage our own members to respond to the police call for information.
"We do not yet know the exact circumstances of these incidents and should not speculate while the investigation continues. However, as the police have now confirmed that there is evidence of illegal poisoning in the deaths of these birds of prey, we condemn this illegal activity unreservedly.
"Wildlife crime of any kind will not be tolerated by the responsible majority of landowners."
As a member of the Partnership for Action Against Wildlife Crime Scotland, SL&E would continue to do whatever it could to help the police and the Scottish Government, working in partnership with agencies and organisations, to eradicate wildlife crime, he said.
Duncan Orr-Ewing, Head of Species and Land Management for RSPB Scotland, said: "This appalling incident highlights the very real threat illegal poisoning poses to fantastic species like red kites.
"An anonymous donor deeply concerned at the illegal killing of the red kites has come forward to increase our reward for information leading to a prosecution to £10,000."