Changes in the marine environment have been blamed for the decline in the numbers of kittiwake over the past three decades.
Numbers of the cliff-nesting gull have more than halved since the mid-1980s across the UK, and populations in Scotland have crashed by almost two thirds, according to the RSPB.
But a cliff-top colony in Splash Point, Seaford, East Sussex, has bucked the trend by adding another 300 pairs to its numbers, a spokeswoman for RSPB South East said. The colony is made up of about 1,100 pairs this year, up from 800 pairs in 2011, which is increasingly significant as kittiwakes struggle to breed in strongholds along the coast of northern England, Scotland and Wales, she said.
Splash point, which is one of the South East's last remaining kittiwake colonies, saw chicks hatching at the beginning of June, which should indicate another successful year for the seabird colony, according to the charity.
In July, the RSPB ran a Date with Nature project at Splash Point where visitors were able to view the kittiwakes as they raised their young.
Kate Whitton, Date with Nature project officer at RSPB South East, said: "Sussex's kittiwake colony seems to be doing well, which is welcome news, especially as another local colony at Newhaven, which has been steadily decreasing over the last few years, had no nesting kittiwakes at all this year."
Early reports of seabird nesting performance from across the UK this summer indicate continuing problems for the kittiwake population, with one breeding colony now extinct and others predicted to disappear within three years, the RSPB said.
Counts of the average number of chicks per nest also seem to be reducing.
Dave Burges, conservation officer for the RSPB in the South East, said: "It now seems beyond doubt that the decline of the kittiwake is being driven by a slump in the availability of sandeels - a staple food for these and many other seabirds.
"It is almost certain that the crash of sandeels is linked to the warming of the sea and subsequent changes in plankton availability.
"In other words, changes at the microscopic level are wreaking havoc at the other end of the food chain."
Although kittiwakes are one of the world's most abundant seabirds, they are declining at an alarming rate, particularly in Orkney and Shetland where around one fifth of the UK population return to breed each year, according to the RSPB.
Mr Burges said: "Seabirds remain largely unprotected at sea and have been marginalised in the identification of new Marine Protected Areas - this obvious gap needs to be filled if we're going to prove we're serious about protecting threatened marine wildlife.
"It is vital to maintain the current tight restrictions on the North Sea's industrial fishery for sandeels to ensure it doesn't add to the wider pressures on sandeel stocks."
The RSPB spokeswoman said there is also evidence from Iceland, Greenland and Norway that the kittiwake population in those places is in decline.
In 2008, the kittiwake was added to an international watch list of threatened species, under the Ospar - Oslo-Paris - Convention, set up to protect the marine environment of the north-east Atlantic, she said.