The discovery of 14 red kites and five buzzards dead in an area of two square miles south east of the village of Conon Bridge near Dingwall has outraged environmental opinion far and wide.
Later today, RSPB Scotland has organised a public demonstration in Inverness condemning those responsible, with life-size replicas of the birds to be carried through the Highland capital.
However, the man who heads the body which advises the Scottish Government on nature has issued a stark warning about the message the persecution is sending out.
Ian Ross, chairman of Scottish Natural Heritage (SNH), said the growing catalogue of the raptors' deaths was "shocking, grim and distressing" and SNH had put considerable resources into the reintroduction of red kites to the Black Isle.
He said: "Nature-based tourism is worth £1.4 billion a year to Scotland's economy.
"It's clear that acts like this detract from that value and diminish Scotland's appeal as a major wildlife tourism destination."
NFU Scotland and Scottish Land and Estates have both condemned the killings of the birds and their members have put up £12,000 to the reward for information, which now stands at around £27,000.