Five red kites and a buzzard were discovered in Ross-shire earlier this week, with police saying they suspect criminal behaviour.
Two further red kites and three more buzzards have now been found in the area around Conon Bridge and Muir of Ord.
Police have not established the cause of death but Detective Inspector Scott McDonald, who is leading the investigation, said earlier this week that "some form of criminality" is suspected due to the close proximity of the deaths.
A police spokesman said: "We are now investigating the deaths of seven red kites and four buzzards, all found around the Conon Bridge - Muir of Ord area.
"Inquiries are ongoing and we continue to appeal for any witnesses who have seen anything suspicious in the area.
"The remains have been taken away for post-mortems and we are awaiting the results of those."
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 chairman Alex Hogg said: "The number of birds being found is hugely worrying and suggests something is very much amiss here.
"We can only reiterate that people should contact Police Scotland if they know anything about what has happened."