The puffin population on the Farne Islands off the Northumberland coast has been declared “stable” after a devastating bird flu outbreak, the National Trust said.

The charity’s team of rangers this year carried out the first full count of the seabird species since 2019 on the remote national nature reserve, finding populations flourishing and avian influenza absent.

The Farnes are an internationally important home to approximately 200,000 seabirds, including puffins, Arctic terns and kittiwakes, all three of which are on the UK’s “red list” of greatest conservation concern.

National Trust rangers had been unable to make a full count of puffins in the last few years due to coronavirus restrictions and then to dealing with devastating waves of avian influenza that spread among seabirds on the islands in 2022 and 2023.

This year, they have finally been able to count the population of puffins – affectionately known as the “clowns of the sea” – across eight of the 28 islands that make up the Farnes.

The National Trust estimates the number of puffins breeding on the islands this summer was around 50,000 pairs, compared to nearly 44,000 in 2019, suggesting a 15% increase in numbers.

Finding bird flu to be absent among the species, the charity said this could mean the seabirds have built a natural resilience to the disease.

The rangers will therefore be able to return to perform their full range of duties daily including bird counts, conservation work and welcoming visitors back to the islands.

Sophia Jackson, a National Trust area ranger on the Farne Islands, said: “We just didn’t know what to expect with this year’s count.

“Annual monitoring is so important in our care of all the birds that live and breed on the islands as it allows us to understand the impacts of climate change, particular weather patterns as well as disease.

“We feared the worse after we sadly collected 938 dead puffins in 2022 and 2023 which had died due to bird flu – but it’s been amazing to get this positive news – and it seems due to the species’ own ‘self-isolating’ behaviours that they have weathered this particular storm.”

Puffins are the only seabirds that lay their eggs in burrows on the vegetated areas of the islands, and typically return to the same burrow each year to breed, the National Trust said.

To conduct the count, the rangers monitor the birds by observing burrows for signs of activity, which includes birds returning to nests with fish in their beaks to feed hungry pufflings.

Occasionally, they will put on gloves and put their arm down into a burrow to gently feel for any pufflings if they are unsure whether it is occupied or not.

Dr Chris Redfern, emeritus professor in the School of Natural and Environmental Sciences at Newcastle University who helped to verify this year’s results, said: “It is very good news that puffin numbers for the Farnes overall are holding up.

“The possible displacement or decline of puffins breeding on the Outer Group of islands is worrying though. It will be important to try and work out why, and whether or not anything can be done to ensure the long-term stability of puffin and other seabird colonies throughout the archipelago.”

The National Trust also shared preliminary results on other counts for cliff-nesting birds, which have yet to be fully collated and verified.

Initial figures show that some species appear to be struggling, particularly shags whose numbers were down by 75% on the inner group of islands while guillemot numbers are 37% lower.

Thomas Hendry, an area ranger for the Farne Islands, called the initial numbers “concerning”.

“Although we didn’t pick up a particularly large number of shags during the two seasons where we experienced bird flu (172 in total), we fear that the more extreme weather and frequent storms during the winter really disrupted their ability to feed,” he said.

“In comparison, guillemots were hit hard by bird flu – with over 3,500 picked up in the two years the islands had to close, and no way of knowing how many more died at sea.

“This is likely due to them being cliff-nesting birds – packing themselves in tightly with the other species that breed in this manner.

“Our aim therefore next year will be to keep a close watch on the seabirds to see if we can see any sign of a recovery pattern, and contribute towards the national seabird monitoring programme so we can better understand the long-term impact of bird flu.”