The first ever arrival of a Pacific seabird in Ireland thousands of miles off course from its destination is the latest in a series of bizarre appearances of Arctic birds on this side of the Atlantic.

The stripy-necked Pacific diver, commonly found in the icy reaches of Alaska and the northwest coast of America, wouldn't have rated a second glance from passers-by in Galway in recent weeks. But it has caused a sensation among Irish birdwatchers.

The first recording of the seabird on our coast coupled with an extremely rare sighting of another Pacific bird, the Thayer's gull, in Ireland a few weeks ago has prompted speculation about climate change.

It is thought the birds could be foraging a new migration path through the Northwest Passage used by explorers – the famous sea route linking the Pacific and Atlantic oceans. The ice-clogged route through the Arctic Ocean has opened up to shipping due to melting ice over the past five years, but it is now thought it has also opened up a new migration route for voyaging birds who need open water to feed along their journey south.

Ornithologist Eric Dempsey, the author of the Complete Guide to Ireland's Birds, said the recording of the Pacific diver in Ireland has led to theories about climate change.

"It's an extraordinarily rare thing and it has caused quite a stir. The sighting in Oranmore in Galway is the first record of a Pacific diver in Ireland and there have been a few seen in Britain in the last year or two.

"The arrival of the Thayer's gull, which is also a Pacific coastal bird, is also very rare.

"We're wondering what is happening. These birds breed in Alaska and winter down the Pacific coast of North America.

"A tufted puffin and a long-billed murrelet, which are also both Pacific species, have also been recorded in Britain in the last year or two. It is puzzling how birds from the Pacific coast who breed in Alaska can be getting into the Atlantic. Birds are great indicators of change. To see these species in Ireland and Britain means something has slightly changed... I'm not a climate expert but it is definitely a possibility," he says.

"These birds can be looked at as lost but I always believe we are in the presence of a great explorers like Scott pushing out the frontier for their species."