Grassholm Update

As this blog is dedicated to both Ramsey and Grassholm we thought it was about time to share some up-to-date information on Grassholm and a summary of the work we have been conducting on the island this year.

Whole island shot of Grassholm on the 26^{th of} August 2022 © Will Richardson.

As many of you may be aware Grassholm was hit by High Pathogenicity Avian Influenza (HPAI) in July of 2022, resulting in large numbers of nesting Gannets dying. Although we knew the colony had been hit hard by the virus in 2022, we didn’t know how badly until we could census the colony again in 2023.

The black eye of a gannet which has contracted HPAI and recovered © Alys Perry.

Since the outbreak we have been limiting landing on Grassholm and instead conducting monthly drone surveillance flights over the island.  This has enabled us to see first-hand how the colony is progressing throughout the season and if there were any signs of HPAI resurfacing. In the spring of 2023, there were no signs of HPAI on Grassholm although the colony was looking very sparse.

During May this year Nia and Greg landed on Grassholm with Professor Steve Votier from Herriot Watt university and his team to deploy GPS tags on breeding adult gannets. This will provide data on their foraging movements and will help us to understand how these birds are responding following the HPAI outbreak the previous year. The positive news from this visit was that despite the low numbers, many birds were behaving normally and incubating eggs. Lots of the birds showed signs of having contracted HPAI in 2022 but survived with only the tell-tale black iris to show off their ordeal.

Throughout the season we landed on Grassholm to do colour ring re-sightings with West Coast Birdwatching in order to establish how many colour ringed adults were left within the population so that we could see how many individuals were surviving year on year. Whilst on these trips we also conducted the gannet productivity surveys to assess what number of adults were attempting to breed following the outbreak. In order to do this, we take a sample of 150 nests at each of the 4 main sections of the island and record whether the nests are empty, contain a small naked chick or large fluffy chick. These results are then added into a calculation that produces the proportion of adults that are successfully breeding each year across the colony. The results this year were at 44% which is a massive reduction from the 79% of the previous year (pre HPAI outbreak). A reason the productivity might have dropped so significantly is because many of the adult gannets present on the island were standing alone over empty nest. So, it’s possible that these birds may have lost their partners during the 2022 outbreak and have not re-paired yet and therefore not attempting to breed this year.

The 2023 Grassholm gannet census was conducted in July and revealed some shocking news. In 2022, before the outbreak 34,491 pairs were recorded on the island. This year only 16,482 pairs were recorded meaning a 52% reduction. The last time the colony was at this level was in 1969, when a count of 16,128 was recorded.

A drone being retrieved after surveying the island during a monthly surveillance trip © Alys Perry.

Unfortunately, shortly after censusing the colony, HPAI was reconfirmed in gannets on Grassholm after 9 dead adult gannets were seen along the edge of the colony.  Three of the dead birds were swabbed and sent off for testing and came back positive. However, the outbreak this year did not appear to be as severe, and we are hoping that there is some level of immunity in the colony.

An immature gannet being GPS tagged © Dave Astins.

No further signs of HPAI were seen in the colony, which meant that our research on the gannets could continue. As a result of the 2022 HPAI outbreak all RSPB and BTO necessary safety measure were put in place to ensure the safety and minimise the spread of HPAI to us and the gannets. This meant full PPE had to be worn when landing or carrying out any fieldwork on Grassholm this year.

Nia and I went out with Steve Votier and his team of researchers in August to collect back the GPS tags that were put out in the spring and deploy GSM GPS tags on both adult and immature gannets. The GSM tags use mobile phone networks to send the data immediately back so that the live movements of the gannets can be seen. Tagging immature birds should give us particularly interesting data on how gannets who are not breeding yet move between colonies. In addition to the tagging more adult gannets were colour ringed so we can continue to monitor adult survival rates and assess how these birds are responding to the HPAI outbreak in the future.

Nia & Steve GSM tagging an immature gannet © Ruth Dunn.

Lisa & I after just landing on Grassholm for a re-sightings trip © Alys Perry.

Looking for colour ringed gannets during a re-sightings trip © Dave Astins. 

Dale Sailing returning to the Dale Princess after dropping us onto the island with the whaley © Alys Perry.

A colour ringed adult and its chick © Alys Perry.

Despite some sad news from the island this year and last year, there is evidence that the gannets on Grassholm are still attempting to breed and have got some large chicks away. This is an ever-changing situation, and no one quite knows how the gannets will respond in the future, but we are hopeful that with time the colony will start to rebuild and thrive again. We will continue to monitor the situation closely over the next few seasons and hopefully we can start updating you with some more positive news.

We would like to say a special thanks to Dave & Lisa from West Coast Birdwatching for allowing us to jump on their trips out to Grassholm to carry out additional productivity and surveillance surveys. A big thank you to Steve Votier and his team from Herriot Watt University for continuing to monitor and research the effects of HPAI on the Grassholm gannets. To Pad at Thousand Islands & Gareth at Dale Sailing for landing us safely on Grassholm throughout the season. And to the drone flight crew Will and Ben for all their efforts on our monthly drone surveillance trips. 

A very large seaweed filled nest © Alys Perry.

Alys & Nia Warden and Assistant Warden of Ramsey & Grassholm Island.