Police are investigating a spate of poisonings at neighbouring Highland Perthshire estates.
Three working dogs and two birds of prey died in what could be malicious attacks in the Edradynate and Pitnacree areas, near Pitlochry.
One theory being explored by wildlife officers is that someone with a grudge against estate owners has been dropping bait laced with illegal substances. The killings have been ongoing for seven months.
In September 2017, Scottish National Heritage imposed strict sanctions on the 4,000-acre Edradynate site, near Aberfeldy, claiming crimes against wildlife were being committed on the land following the discovery of two poisoned buzzards.
The estate’s general licences to control wild birds, by shooting or trapping, were effectively revoked for three years.
A Police Scotland Wildlife Crime Liaison Officer said: “The owners are understandably extremely upset at the loss of their dogs.
“Once again, we also find ourselves investigating the illegal killing of raptors and this is extremely disappointing.”
He said: “The poisons which have been used in both cases are illegal poisons and have been banned from use in the UK for many years.
“We have searched the areas and our investigations to date would suggest that there is not a wider threat to public safety.
“However, all members of the public in the area are asked to remain vigilant and report any suspicious behaviour, especially during the hours of darkness.”
A spokesman for the Edradynate estate said: “These are appalling incidents that have affected local estates and farms.
“We reported a number of these incidents to Police Scotland and have been working closely with them to provide help to the investigation but in spite of this, we have most recently seen the terrible death by poisoning of a sheepdog when it was most needed during the lambing period.”
He added: “We would urge anyone with information, especially if they see anything suspicious late at night, to contact Police Scotland as soon as possible.”
Environment Secretary Roseanna Cunningham said she was appalled to hear about the killings.
“It is particularly disturbing that they have been poisoned,” she said. “As we have seen a sharp reduction in this type of wildlife crime in recent years.
“The use of poison is not only illegal, it is cruel and barbaric and threatens all kinds of wildlife and domestic animals which come into contact with it. There is absolutely no excuse for this kind of criminal behaviour.”