ROBINS are as festive as Santa and grace as many Christmas cards as baubles and bells, but beneath their jolly red breasts lurks an aggressive and murderous intent.
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For experts have discovered the festive songbirds think nothing of bumping off their rivals to ensure they can get their beaks into enough food to survive.
Footprints in the snow at a Scottish nature reserve alerted conservation workers to the robins' criminal underworld when clusters of feathers from one bird were found surrounded by tracks made by another.
Experts believe about one in ten robins is brutally murdered by another bird of the same species, as both males and females become embroiled in vicious battles over territory and food.
Other prints found in the snow in Fife gave workers clues to numerous other scuffles, where one bird which dared to venture on to another's feeding ground had been attacked and seen off by the incumbent.
"Traditional images of peaceful robins adorn our Christmas cards at this time of year, but this harmless looking bird is actually a territorial terror," said Tom Cunningham, reserve manager for Scottish Natural Heritage at Tentsmuir National Nature Reserve.
"As well as defending territory during mating, they will often fight other robins, sometimes to the death, over scarce food resources in winter."
Mr Cunningham believes the birds' most recent scraps have been sparked by hunger - as their usual food sources are buried beneath the heavy snow that has swept Scotland.
"A lot of birds and animals are starving this winter," he said. "It's not surprising that they're fighting each other for what they can get - it's survival of the fittest at the moment. They really are territorial creatures."
But Louise Smith, of RSPB Scotland, claimed the birds were using the food shortages as an excuse to start a brawl. "Many people will be surprised to learn that this sort of behaviour is fairly common for robins," she said.
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"Perhaps the lack of food around at the moment aggravates this behaviour, but the fact is that robins don't need this excuse to start brawling and it's possible that, even without the bad weather, we'd still be hearing similar stories."
She added that both male and female birds regularly got involved in violent fights over territory. "Robins are aggressively territorial - in fact, they are possibly the most territorial bird in the UK - and they don't just defend territories in the breeding season, like most other birds," Ms Smith said.
"Nor is it just the males that do this. Their famous plumage is what triggers this aggressive behaviour, with the sight of another red-breasted intruder enough to start a serious fight between the two birds.Mostly, the loser quickly flees and both birds go about their normal business again, but it is believed that about 10 per cent of robins die at the hands - or rather beaks - of another robin."
A robin can use up to 10 per cent of its body weight during one winter night, and unless it can find enough food daily to replenish these reserves, it will die.
l The birds are thought to have become associated with the festive period after Victorian postmen who delivered the first Christmas cards were dubbed "robins" due to their red tunics.