U.K. wildlife officials are worried about one of the world’s rarest birds after a flock of light-bellied brent geese went missing during their annual migration out of the Arctic. According to the Independent, 2,000 of the 6,000 geese failed to arrive at their usual winter feeding ground of Lindisfarne National Nature Reserve (NNR).

During the summer, the birds breed on Svalbard and Franz Josef Islands in northeast Greenland, but they fly south as winter approaches to avoid the harsh Arctic winter. Most of the rare geese winter in Denmark but extreme winter weather (which could be the result of climate change) has caused the Danish wetlands to freeze over this year. This forced the geese to find new feeding grounds.

They were expected to join the rest of their species at Lindisfarne NNR but never arrived.

Natural England’s Lindisfarne NNR manager Andrew Craggs said, “It is a sign of just how widespread the big freeze has been that these geese are present at Lindisfarne in such large numbers. The arrival of the geese is a treat for wildlife watchers, but it is a sobering thought that virtually the entire world population of these birds rely on only a couple of locations in Europe for their survival in winter.”

Half of the light-bellied-brent geese usually winter at the Lindisfarne NNR and the rest in the Danish wetlands. Craggs said this year’s freeze resulted in the largest recorded number of birds to arrive at Lindisfarne in years.

Hopefully the rest found hospitable feeding grounds of their own and will join their kin back in the Arctic this summer as usual.