An aggressive elite of great skuas is increasingly ditching a diet of fish in favour of eating other seabirds. The dietary switch among a super-fit minority of the species is being blamed for a fall in numbers of some bird colonies in Shetland.
Experts are predicting that fishery regulations introduced this year could force even more great skuas to turn on their neighbours by reducing the amount of discarded fish that the species often feeds on.
Steve Votier, an expert from Glasgow University who has spent two years, with the support of the Royal Society for the Protection of Birds, studying the habits of great skuas in Shetland, said it was likely the incidence of predation would rise.
"Shortages in food supplies, namely discarded fish, may result in an increased number of skuas feeding on seabirds, though it is still a small number of individuals that are a cause for concern," he said.
The large gull-like species of seabird, whose numbers are growing in Scotland, is noted for its aggression.
Mr Votier, however, said that most of the great skua population was content to persist with a diet that mostly consisted of fish.
It was a small proportion of each colony, less than 10 per cent of the total, that was found to specialise in hunting other birds. These specialists appeared to have greater levels of fitness than their counterparts and tended to be found in the smaller colonies.
The great skua's ability to exploit a wide range of food sources, the key to its success, meant that many could be disuaded from pursuing other seabirds by man directly feeding specific pairs of birds. Mr Votier suggested this may be the only legal way to curb the growing onslaught.