The warning was made after Police Scotland announced it was investigating the suspected poisoned bait found on open ground in the Carmichael area of South Lanarkshire. The bait was recovered yesterday along with the carcass of a wild bird. It will now be sent for forensic analysis.
Ian Thomson, RSPB Scotland's head of investigations officer, said: "If people are leaving poison out in the countryside, which has been a crime for over a century, it could affect not just protected birds and animals but potentially pets and even humans. Some of the chemicals used are extremely toxic and can be fatal even if they just come into contact with the skin."
Mr Thomson said there had been a decline in detected poisoning in the past three or four years, which was to be welcomed.
"However 2013 seemed to suggest there had been a bit of a resurgence in poisoning activity," he said. "At the end of the year there was the well publicised case of a golden eagle being illegally poisoned up in Angus. The figures aren't out yet but from what I hear there has been a rise last year."
But he said people who were targeting birds of prey with poison were also using other methods such as shooting, trapping and destroying nests. "Certainly there has been no sign in a let-up in that, which is pretty depressing," he said.
The Partnership for Action Against Wildlife Crime said in September last year that other forms of persecutions of birds, such as egg theft, trapping and shooting remained high.
The landowners' organisation Scottish Land and Estates and the Scottish Gamekeepers Association have both been active in trying to stamp out the poisoning of birds of prey.