[Photo] The red kites are under increased threat, the study revealed.

The illegal abuse of red kites is having a devastating impact on their population, according to new research.

RSPB Scotland said landowners were still laying poison baits and shooting the birds, which are often seen as a threat to game, poultry and livestock.

The charity's study found that an estimated 185 birds were killed between 1999 and 2006 - an average of 23 birds per year.

The RSPB said the figures may not indicate the full scale of the problem.

The organisation's scientists believe the corpses of birds killed deliberately were more likely to be hidden or disposed of than those that had died naturally.

They believed that the research could also indicate what is happening to other bird of prey populations.

The practice of laying poisoned baits, normally in the form of agricultural pesticides, has been illegal since the 1900s.

Red kites are rarely the intended victims as they are largely scavengers but their carrion feeding makes them likely to find any poisoned meat left lying around.

Duncan Orr Ewing, head of species and land management for RSPB Scotland, said: "It is time for the fine rhetoric about tackling illegal poisoning to be turned into action on the ground.

"Everybody seems to agree that this activity is reprehensible. However, cases involving the deliberate killing of some of our rarest birds of prey, like the red kite, occur year after year in Scotland.

"It may take a custodial sentence before people engaged with this activity begin to take the matters seriously."

Deputy Environment Minister Rhona Brankin said: "The continuing persecution of red kites in Scotland revealed in these figures is deplorable, irresponsible and criminal.

"The misuse of pesticides does not affect birds of prey in isolation but has potentially harmful consequences for all life in the countryside."