Bardsey Island - Ynys Enlli - the island of 20,000 saints and home to razorbills and kittiwake amongst other amazing seabirds. From its ruined monastery, gnarled and twisted apple tree, growing by the side of Plas Bach, to the lighthouse standing on the southern tip of the island - Bardsey is an ideal (and picturesque) location for tracking UK seabirds. So throughout the summer nesting season of 2011 the RSPB undertook a range of tracking studies at Bardsey, focusing on razorbills and kittiwakes.
Field staff had the arduous task of scrambling across rocks and venturing round cliffs to tag both species with two different, and very clever tags. We used a mixture of GPS tags, which let us know how far and where the birds are travelling to feed, and TDR (Time, depth recorders) that give an amazing insight into the birds activity under the water. The GPS tracks show us where the birds went, but the critical question is why. By matching the habitat (i.e. seabed type, bathymetry, sea-surface temperature, tidal fronts etc.) to where the birds foraged important links can be made showing which at-sea habitats are most important for seabirds foraging from breeding colonies. The habitat often influences the type and reliability of prey, which are important when seabirds are under pressure to feed themselves and chicks.
For the razorbills, GPS tags and TDR were used, and care was taken to ensure very little disturbance was caused to the adults. Caught by hand and quickly released back into their burrows to be with their eggs and chicks, a total of 21 tags gave accurate data back.
The razorbills foraged to the west, within 40km of the island, although dive depths were typically less than 15 metres we recorded a maximum dive depth of 97m – quite a feat for a bird only 40cm! Many of the birds staying away overnight tended to rest on the water, drifting for many kilometres in the Irish Sea with the ebb and flow of the tides.
Being surface feeders , the kittiwakes were tagged with GPS only, and foraged in all directions within 40 kilometres of Bardsey Island. Typically they flew fairly direct from the colony, until spotting an area for likely prey, at which point where track became more sinuous as they searched for food. The tags also showed that at night, they would rest on the water drifting with the tides.
For both species the tags showed that the waters near to Bardsey were used for grooming, socialising and resting near the colony. It appears that the birds travel further from the colony to the areas where they are likely to forage.
The data from this study was compared with other UK colonies (FAME Project: RSPB unpublished data). It appears that the razorbills and kittiwakes from Bardsey forage relatively close to the colony and razorbills made fairly shallow dives which suggests that the conditions for Bardsey seabirds were favourable during the period of this study.
So what next and how are we using this information? For starters this helps show that birds from protected sites use the waters near to their roosts for a number of reasons, giving weight to our calls on Government to extend the protected areas around existing seabird sites. The range that the birds travel also helps to highlight that whilst we protect the roosting areas, we currently fail to protect where the birds feed - A lovely home, but no food in the cupboards!
This year we have expanded the studies across more Welsh Islands, including Grassholm, Puffin, Skomer and Ramsey. We hope to publish the results around December – check back then to see what effect this summers awful weather has had on Welsh Seabirds!
All images courtesy RSPB images