ONE of the rarest birds in Scotland is producing chicks with “lethal blindness” as a result of inbreeding.
There are only 60 breeding pairs of red-billed choughs in Scotland – nesting on the remote Hebridean islands of Colonsay and Islay.
The birds are remarkable for their brightly coloured crimson bills and their mischievous acrobatic behaviour.
But new research by the University of Aberdeen – published in the Journal of Animal Ecology – has revealed that newly-hatched birds are being born blind due to inbreeding on the islands.
The study shows that 3% of chough chicks born in Scotland every year since 1998 are now born blind.
29 “nestlings” – young birds that have yet to leave the nest – have been hatched blind by nine pairs of parents since the first case was recorded in 1998.
The chicks are otherwise healthy and survive in the nest when they are fed by their parents.
But once they leave the nest they are unable to care for themselves and die.
As a result the paper refers to their impairment as “lethal blindness”.
And – according to the research – the parent pairs which are hatching blind chicks are even breeding more than their healthy counterparts.
This could mean that the problem increases in the coming years.
Previous research has suggested that the blindness is a result of changes in their environment.
But the new research has proven that the blindness is a result of a recessive gene spreading through the small inbred population of the iconic island birds.
Amanda Trask, a PHD student at the University of Aberdeen who undertook the study said: “Choughs are now very rare in the UK and there are just two populations remaining in Scotland, on the Islands of Islay and Colonsay.
“Our research shows that the blindness mutation is likely to persist in the population into the future despite being lethal in blind individuals.
“This is because non-blind individuals that carry the mutant gene produce large numbers of chicks per year, causing the mutation to be passed into the next generation.”
Red-billed Choughs are mainly native to North Africa, Central Asia and China, and are in the same family as the common crow.
According to folklore – recorded by Robinson Crusoe author Daniel Defoe – the birds enjoy stealing burning candles and firewood from homes to set alight to thatched houses and haybales.
It is also said that when he died King Arthur’s soul migrated into the body of a chough – whose bill and legs were red as a result of the blood he spilled in battle.