Rarity finders: Bridled Tern in Gwynedd


By early August, the tern nesting season is nearly over and many birds have started to leave their breeding grounds. At this time of year, terns roost on beaches across North Wales, and if you're lucky, you can encounter all five British-breeding species in a single day, including Roseate Tern. This is an exciting prospect for any birder, but it was not why I was scanning through terns at Hafan-y-Môr on Sunday 6 August.

There are colour-ringing projects carried by dedicated BTO-licensed bird ringers for all tern species nesting in Britain. Tern colour rings have unique codes which are readable in the field, and these projects allow better monitoring of movements and survival than using metal rings alone. In 2021, a scientific paper was published demonstrating the interchange of individuals between Little Tern colonies across Britain, Ireland and Isle of Man. One fledgling, ringed as a chick on 27 June 2018 at Kilcoole, Co Wicklow, was seen nearly a month later on 24 July at Gronant beach, Clwyd. Five days later, it was back in Ireland at Portrane, Co Dublin, having carried out two crossings of the Irish Sea in quick succession. This bird would have made at least one more crossing on its migration south to Africa. Discovering these movements adds a new dimension to birding.

In recent years, some birders in North Wales have been encouraging each other to look more closely for colour rings on Sandwich Terns. On Sunday 30 July, local birder and ringer, Robin Sandham, had a very successful trip to Hafan-y-Môr on the Llŷn peninsula, re-sighting seven colour-ringed Sandwich Terns, one Common Tern, three Mediterranean Gulls and a Kittiwake. The Common Tern was colour ringed earlier this year by a Dutch ringing group in Senegal, but it had been metal ringed 24 years prior as a chick on the Anglesey coast. Having recently moved nearby, I decided to visit myself on Saturday 5 August. After a very late night ringing Sandwich Terns with Tony Cross at Ynyslas near Aberystwyth, I didn't arrive until mid-day, when it was already high tide. I waited patiently as the tide receded, and terns started landing on the rocks below Hafan-y-Môr caravan site. I only managed three colour-ring sightings before the birds moved out of range. These birds had been ringed in Mid Wales, Cumbria and Scotland respectively. Frustrated with my efforts, I decided to return early the next day.

On Sunday 6 August, I was on the beach at Afonwen by 8 am and Sandwich Terns were already waiting for me on the shoreline. I managed five colour-ring re-sightings before the birds moved off towards the rocks below Hafan-y-Môr. I walked up to the cliff-top and waited patiently for the Sandwich Terns to move closer. After an hour, the inscriptions on the colour rings were readable. I was just getting into the swing of it, carefully checking the legs of each bird through my scope, when a tern with a black head, white forehead and dark wings landed in front of me. I couldn't digiscope it because my phone had ran out of battery so I turned to a new page in my notebook and frantically started drawing. I noted a black eyestripe which extended past the eye, a grey-brown back and a black trailing edge to the wing. After less than a minute, the unexpected tern had taken off and disappeared. I wasn't 100% certain on the species so I decided to head back to the car, charge my phone and check the Collins Bird Guide app.

Jack didn't have a camera to hand when the Bridled Tern appeared, but it was well photographed by those who made the journey to see it (Alan Boddington).

It didn't take long for me to realise that I had most likely seen an adult Bridled Tern. I immediately phoned my friend Reg Thorpe, who confirmed my identification based on the features that I had described. Bridled Tern's mega-rarity status was unbeknown to me, but Reg's eagerness to tell his friends and get to Hafan-y-Môr should have been a sign. I put the news out on the local rare bird news WhatsApp Group, and understandably, my initial message was met with scepticism because I didn't have any photographic evidence. After a couple of hours, Reg and his friends, Simon Hugheston-Roberts, Eddie Urbanski and Rhys Jones had relocated the Bridled Tern and when their photos started to appear on WhatsApp group, the interest really took off. For the next three days, the tern would come and go from the rocks below Hafan-y-Môr, providing good views for those who had timed their visit correctly, often fishing and interacting with the Sandwich and Common Terns present. At one point, there were at least 40 birders looking for it along the Wales Coast Path.

Bridled Terns are found breeding in tropical oceans from the eastern Caribbean to the west coast of Africa. There have only been 25 previous records in Britain, of which two were in Wales. This would be the third for Wales, and the first for Gwynedd. The bird had disappeared by Thursday 10 August, hopefully on its way back to the tropics.

In all honesty, I would never have found this rare tern if I was not looking for colour rings. In addition to the Bridled Tern, I found 13 colour-ringed Sandwich Terns on the same day: seven ringed at breeding sites in Cumbria (one), Northumberland (one), Ireland (three) and Holland (two), as well as six ringed at a migration site in Mid Wales. One of these birds breeds at Cemlyn, but had also been re-sighted in winter at Swakpomund, Namibia, more than 8,500 km away. Colour-ring sightings provide a fascinating insight into the life of birds, and generates data which can be used for their conservation. You never know when a rarity might turn up as well. There may be a Sooty Tern out there next summer!

You can find contact details for reporting colour ring re-sightings at European Colour-Ring Birding.



Wilson, L, Rendell-Read, S, Brown, C, Candelin, G, Cook, H, Hales, S, Lock, L, Newon, S, Norman, D, Samson, L, Slattery, J, Williams, L, and Bolton, M. 2021. Insights from colour-ringing Little Terns across Britain, Ireland and Isle of Man. British Birds, 114(2): 97-116.

Written by: Jack Slattery

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