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Polar bears are raiding the nests of seabirds for eggs as the melting of the Arctic sea ice is forcing them to spend more time on land, according to a new study.

Biologists have found that polar bears are spending an increasing amount of time in bird colonies each year as they search for alternative source of food during the breeding season.

They say that the date the bears begin arriving to raid the bird nests is now almost a month earlier than it was 10 years ago when the behaviour was first seen.

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Polar bears, like the one above raiding barnacle geese nests on Svalbard, Norway are preying on sea bird eggs

Scientists say that 90 per cent of all nests in the bird colonies they observed were raided by the polar bears.

They warn that as melting of the Arctic sea ice makes it harder for the bears to reach their traditional prey - seals - then their impact on sea birds will increase.

Dr Jouke Prop, from the faculty of Arctic studies at the University of Groningen in the Netherlands, said: 'When a new predator enters the scene, the delicate balance between predators and their prey may be perturbed.

'Polar bears colonizing coastal areas, from which they have been absent for a long time, is an example of this situation.

'The east coast of Greenland hosts a polar bear population that used to roam the extensive drift ice offshore, only infrequently showing up at coastal tundra sites.

'The bears that we observed during the past years were either in transit or they were extensively feeding on eggs in bird colonies.

'Polar bear predation was particularly severe on offshore island colonies of barnacle geese, common eiders and glaucous gulls.

'Some polar bears also preyed on aggregations of pink-footed goose nests further inland.'

Dr Prop and his colleagues, whose research is published in the journal Frontiers in Ecology and Evolution, fount that levels of predation of seabird nests by polar bears correlated with diminishing sea ice coverage.

They combined Nasa satellite images of the extent of sea ice around Greenland and Spitsbergen, Svalbard in Norway with observations in seabird colonies there.

They found that as the length of the summer sea ice season has reduced by around 3.5 days a year, the number of days polar bears spent on land also increased by around three days.

The bears are now arriving at the bird colonies nearly 30 days earlier than they did ten years ago. 

The researchers saw bears preying on seabirds nests on Traill Island in east Greenland (A), and Svalbard (B)

The barnacle geese above look on helplessly as a polar bear eats the eggs in their nests on the ground

Dr Prop says that he first saw polar bears raid the nests of sea birds at Nordenskioldkysten in Svalbard in 2004.

He said that the bears were able to eat more than 200 eggs within two hours and last year no chicks of any species nesting there survived.

In other locations - such as Belsund, Kongsfjorden, and Hornsund on Svalbard and Traill Island in East Greenland - up to 90 per cent of the nests were raided by the bears.

Dr Prop, an ornithologist, believes that the polar bears have learned a new behaviour and return to the same sites each year to feed on the eggs.

Polar bear feeding in barnacle geese colony

Visualising melting Arctic ice over the past 27 years

He says he has also seen polar bear cubs learning the behaviour from adults by rolling eggs on the ground like balls before eating them.

Dr Prop and his colleagues warn that it is unlikely that the bird colonies will be able to support any more polar bears and the bird colonies may even leave the area in the face of further predation.

They said: 'The number of polar bears exploiting the coastal habitat was small, and we suspect that there is little scope for further increase in numbers.

'This underlines the importance of the sea ice habitrat to support current population levels of polar bears.'