Six birds of prey have been found dead in the Highlands over the last week.
Police investigating the discovery of five red kites and a buzzard in Ross-shire suspect criminal behaviour.
The birds were found in the area around Conon Bridge and Muir of Ord over the period from March 17 to 24.
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Gamekeepers appealed for anyone with information to assist officers following the "disappointing" discovery.
Detective Inspector Scott McDonald, who is leading the investigation, said: "At this time we are unclear as to what has caused the death of these birds but given all the circumstances and the close proximity of them being found we must assume at this stage some form of criminality.
"I would ask anyone who has been working on the land or using the area for recreational purposes to contact us if they have seen anything suspicious that may be linked to this incident."
Police advised anyone who finds any further dead bird of prey to note its location and inform officers, without attempting to recover it.
Scottish Gamekeepers Association (SGA) chairman Alex Hogg said: "This is a hugely disappointing discovery and we would ask anyone who knows anything about this mindless act to contact Police Scotland and to assist with the investigation.
"Clearly, until the post-mortem and toxicology reports are known, there is little information to go on. However, the SGA condemns wildlife crime and advocates only legal means to solving conflicts."
Douglas McAdam, chief executive of Scottish Land & Estates, said: "Whilst it is still unclear how the birds died and important not to prejudge the outcome of the investigation, we support Police Scotland as they continue to gather evidence about these incidents. We would encourage our own members to respond to the police call for information.
"If there is found to be some form of criminality involved in the deaths of these birds of prey then this is something that we would wholeheartedly condemn. Wildlife crime of any kind will not be tolerated by the responsible majority."