A third red kite has been poisoned with a banned pesticide in Perthshire, police have said.
The estate's owners said they were "appalled" by the killing
The dead bird was found on the edge of the Glenturret Estate near Crieff.
Two other red kites have also been killed this year and tests have shown all the birds had eaten bait laced with carbofuran, which was outlawed in 2001.
Tayside Police have appealed for information about the deaths, which have been called "sickening" and "an absolute disgrace".
The force's wildlife and environment officer said those involved in the deaths should "hang their head in shame."
Alan Stewart said: "It is an absolute disgrace that a method commonly employed to kill birds of prey two centuries ago is still in use in 2007.
"Pesticides can easily kill people as well as wildlife yet these deadly baits are still left out in the open.
"Last year saw the highest incidence of poisoning of birds of prey in more than a decade and this could well be equalled if not overtaken in 2007."
He added that it would be "naive" to think the three dead red kites found in Tayside were the only poisoning incidents this year, as most baits and victims were never reported to the police.
Glenturret Estate is home to a number of birds of prey, including golden eagles, hen harriers, red kites and buzzards.
The estate's owners said they were "appalled" by the deaths and were "fully supportive" of the police investigation.
Police said bird poisonings were difficult to solve because they took place in remote areas.
In addition, the birds sometimes managed to fly some distance away from the bait, although they were usually found close by.
The Royal Society for the Protection of Birds (RSPB) Scotland said red kites were scavengers and particularly vulnerable to poisoned baits.
Head of investigations, Bob Elliot, said: "Yet again, carbofuran, a substance banned since 2001, has been used to illegally kill one of our most magnificent birds of prey.
"It illustrates that there are still several people out there content to break the law and recklessly endanger the public.
"Those convicted of these sickening crimes must be punished accordingly, as the regularity with which we see them committed suggests that there just isn't a strong deterrent."
The red kite is one of the rarest bird species in the UK and is being reintroduced in Scotland.