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Wales’ biggest Gannet colony suffers severe population crash

06 Sep 2023 4 minute read
Grassholm Gannets. Photo Mary Gillham Archive Project is licensed under CC BY 2.0.

The population of Wales’ largest gannet colony on Grassholm has halved, according to a recent survey by RSPB Cymru.

The small island, 11 miles off St Davids Head in Pembrokeshire, is normally home to up to 36,000 pairs of Northern Gannets.

It’s one of two gannet colonies found in Wales and is the third largest in the UK.

Prior to 2022, Grassholm used to hold just under 10% of the world population of Northern Gannets.

However, following the 2023 Grassholm Gannet Census in July, conducted by RSPB Cymru and funded by Natural Resources Wales (NRW), the number of gannets nesting on the island this year has plunged dramatically.

In 2022, 34,491 pairs were recorded on the island, but it is down to 16,482 this year – a 52% reduction. The last time the colony was at this level was in 1969, when a count of 16,128 was recorded.

By analysing aerial images taken by a drone, it has been possible to identify significant areas of empty nests and greatly reduced density of birds on the island.

In normal conditions, two thirds of the island should be taken up by gannets who nest cheek by jowl, but this year large gaps have appeared.

This population crash is down to deaths caused by the Highly Pathogenic Avian Influenza (bird flu) outbreak at the colony last year.

Large declines following avian flu have also been recorded at other colonies across the UK including Troup Head in Scotland, suggesting that large numbers of birds have died.

In 2022, the colony was hit by avian flu, with a conservative estimate around the number of birds lost.


However, this year’s drone count has shown this was clearly a significant underestimate and highlights the importance of good science to accurately monitor our seabird colonies.

Greg Morgan, RSPB Ramsey and Grassholm Island Site Manager, said: “Given the substantial gaps we were seeing in the colony this year, a significant decrease was expected, but we didn’t expect it to be this stark.

The gannet colony of Grassholm is one of Wales’ wildlife wonders, and it is extremely disheartening to see this magnificent location suffering a severe population decline. It will take years for the colony to recover, as gannets can be five years old before they start breeding.

“This sad news acts as yet another example of why we desperately need to prioritise reducing the threats that seabirds face, from deadly diseases to climate change.”

Matty Murphy, NRW’s Lead Specialist Advisor for Marine Species said: “The reduction in the number of gannets on Grassholm, in what was once the third biggest colony in the world, is very worrying news.

“However, there is hope, as the mortality of gannets this year was at a much lower level than last summer, which may be a sign of immunity in the population. Wales also has a new, burgeoning second gannet colony on Middle Mouse island, north Anglesey, which will hopefully make our Welsh gannet population more resilient into the future”.

Avian flu has been recorded on Grassholm again this year, with a group of eight birds found dead in July 2023.

So far this appears to be a localised, small outbreak. There may be immunity in the remaining population, but the level of this is unknown without testing healthy birds.

The dominant strain of avian flu in UK wild birds in 2023 is also genetically different to that of 2022 so it is a complicated picture with the virus continuing to evolve.

If members of the public find dead/dying birds on beaches and coastal areas, do not touch them and keep dogs away, they’re encouraged to use the online reporting system or call the Defra helpline (03459 33 55 77).

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