16.01.2025 - Indoor Meeting: Manx Shearwaters at Bardsey Observatory

​Speaker: Steve Stansfield
Reporter: Sue Gale

Steve Stansfield lives in Norfolk for the winter, but since 1998 he has lived and worked on Bardsey Island (Enlli) for the rest of each year. He is now Director of Operations and works closely with Bangor University to study the Manx Shearwaters. He started his talk with a recording of the wonderful cries of tens of thousands of Manxies, which happen all night every night from March to September. Such an evocative way to start a talk, even if it did leave us wondering how anyone got any sleep. On a clear night it would obviously be a pleasure to be awake – Bardsey is now an International Dark Sky Sanctuary, the only place in Europe to boast such a designation. It would be worth a visit just to see the Milky Way on all its glory.

When not stargazing, Steve’s main job is to monitor the wildlife of the island and keep track of migrants. Breeding birds survey include around 250 pairs of Puffins, 150-200 pairs of Storm Petrels, but, in particular, his favourite Manx Shearwaters. These are Procellariiformes, also known as tubenoses, from the same family as Storm Petrels and Albatrosses. The tubes help them to detect food, but also to expel excess salt from the body. The highly concentrated salt solution excreted from the tubes gives the appearance of a runny nose! The Manxies are currently classified as Puffinus puffinus, and they have a huge range of 120 million square kilometres out across the Atlantic. Their breeding range, by contrast, is tiny. 93% of the world population breeds on a group of four British islands, 95% of these in Wales and the remainder on Rum in Scotland.
Manxies are increasing rapidly on Bardsey, from the 30-40 pairs recorded in 1919 to the most recent count of 26,423 pairs. It is an enormous task to count all the burrows on the island and determine if they are occupied, so much so that the count is now split over 4 years. Then there are two years off before the next count is due. The parenting strategy of the Manxies is somewhat bizarre. The single white egg is incubated for 55 days by both parents, who then continue to feed the hatchling for another ten days, very intensively. So much so that the chick grows much larger than the parents, reaching on average 550-600g and the size of a small football. They are too large to exit the burrows, and at this stage the parents leave them to grow adult feathers and slim down, before fledging! Manxies migrate to South America, travelling down the coast of Africa and then across to Argentina and Brazil. Here they stay until maturity, at 4 years of age.
The return route follows the American coast, and then across to
Bardsey where adults return to the same nesting hole every year.
This makes it easy to record the age of ringed individuals, who may
need several replacement rings during their lifetime. The oldest
known are thought to be approaching 60.
Since 2016 tracking devices have provided more detailed information about the range and feeding areas, and as the birds return to the same burrow each year it is easy to recover devices that do not transmit data and have to be removed for analysis. It was soon established that for feeding, birds largely headed for the North Sea Front, where warm and cold-water mix and food is abundant, not the Bay of Biscay as tradition had it. Some however were found to have gone as far as the Scottish Islands. The field work was done on Bardsey but analysis took place at Bangor University, which has collaborated with Bardsey on Manx Shearwater research since 2019. Since 2022 the well-funded Shearwater Project has allowed use of improved tags that include solar panels so they last for longer, and accelerometers that allow speed, wingbeat and orientation to be studied. Pressure sensors have shown that Manxies can dive to depths of 50 meters, when previously it had been thought they were only shallow divers. Heart monitors have demonstrated heartbeats of about 260bpm.
A research project using DNA collected from inside the mouth can identify prey items. The results from one 6-day trip showed 99% of the prey was Sprats. Information about the area covered continues to increase, showing that many birds travelled to Iceland in 2023 on feeding trips. More information about migration will be gained from geolocators affixed to the legs that can be left on over winter. And Steve and his colleagues have sited 35 Manxie nestboxes on Bardsey. These will enable chicks to be examined and rings to be fitted with ease by merely lifting a lid.
It was really exciting to hear about all the research that continues with Bangor University. Steve’s own great enthusiasm was echoed by members who asked more questions at the end of the talk than I can remember hearing before. All were very grateful to Steve for allowing us to hear about such current work, and for taking the time to talk to us.