By Martin Cassidy
Rural Affairs Correspondent
Strangford Lough is home to Brent Geese from Canada
The world's biggest population of Brent geese on Strangford Lough has fallen sharply this year.
Scientists report that few juvenile birds have managed to make the gruelling journey from their breeding grounds in the high Arctic.
A record 35,000 geese returned to winter on Strangford Lough last year but numbers have fallen to 28,000 and significantly the flock contains few juvenile birds.
So what's gone wrong?
No one knows for sure but James Orr of the Wildfowl and Wetlands Trust believes a number of factors may be involved.
"There are reports that it was a late spring in the Arctic that would reduce the narrow window in which the geese have to rear their young," he said.
Brent geese travel an exhausting 2,900 miles from Northern Ireland, stopping off in Iceland and Greenland before arriving at their summer breeding grounds in Canada's high Arctic.
A late spring would mean that food would be in short supply when the goslings hatched out and if foxes were short of food they may have preyed heavily on the flightless young geese.
James Orr says its also possible that the geese may not have been in good enough condition when leaving Strangford and simply were not carrying enough fat reserves to rear young.
"We know that they don't necessarily breed every summer and last year there was a record population," he said.
While the reduction in geese numbers is being studied closely, so far the Wildfowl and Wetland Trust says its not unduly concerned.
"We know that most geese live for between eight and 12 years and some birds are up into their 20s," says James Orr.
The WWT says that 28,000 birds is still a very healthy population.
The hope is that the birds will winter well on the eel grass which grows on the muddy flats of Strangford and fly off in good condition next spring.
The loss of the juvenile section of the flock though underlines just how sensitive Brent geese are to even small environmental changes.