The brent geese are now starting to return to Siberia for the summer
A decline in Hampshire's population of brent geese may be caused by climate change, the RSPB has warned.
The bird conservation charity said the wintering flock in Langstone Harbour nature reserve, near Portsmouth, was producing too few chicks.
It said last year's chicks made up only only 1% of the flock but the figure should be 15% for it to stay healthy.
The UK population of dark-bellied brent geese breed in Siberia, before wintering in the south coast harbours.
Chris Cockburn, RSPB Langstone Harbour warden, said: "It's been yet another poor breeding year for brent geese. When I was out the other day, I counted only seven youngsters in 800 birds.
"To keep population levels stable, around 15% of a wintering flock should be young. This year, it's less than 1%.
"What we are dealing with is an ageing population, and that's bad news."
The brent geese spend the winter in the tidal Langstone Harbour
He said the lack of young is thought to be caused by climate change and an increased number of young chicks and eggs being taken by Arctic foxes.
Mr Cockburn added: "These brent geese breed in one of the coldest places on earth.
"It's here, at the extreme end of the temperature spectrum, that any changes to climate will be first felt.
"A rise of less than one degree there will have a noticeable impact on the ecology of the area. These tremors can then be felt all the way here in Portsmouth.
"The flock is now beginning to return to Siberia, let's hope they bring more young back next year."
South east Hampshire, which includes the Chichester and Langstone Harbours Special Protection Area (SPA), is home to more than 10% of the world's brent goose population and up to 30% of that in the UK, the RSPB said.
Their habit of wintering in a relatively small number of UK sites has led brent geese to become amber listed as a "species of conservation concern".