The Sandwich tern is an eagerly awaited returning summer migrant as it is one of the earliest birds to arrive back to the UK after spending the winter in colonies along the west and South African coast.

The first sightings on the south coast of the UK are generally in mid-March, which is no mean feat given the journey they have to undertake.  As I write, the colony at Cemlyn is increasing in numbers daily and the terns are starting to settle on both of  the lagoon islands. There are regular updates on our Cemlyn wardens facebook page.  Our wardens provided an insight into their amazing journeys.

Sandwich terns have a relatively small breeding range in Europe as shown in yellow below. But their large winter range (in orange) is much more impressive and birds from across Europe will winter together along the coast of Africa.  Many Sandwich terns will make the entire journey from the south coast of Africa, stopping off at hotspots on route to return to UK breeding sites.

The Cape of Good Hope, a peninsular south of Cape town, is the starting point for many Sandwich terns. They will then mostly hug the coast as they travel through Namibia, Angola, Nigeria, and so on. Dakar in Senegal which juts out into the N Atlantic seems is another marked congregation point, which sees large swathes of migrating birds, with one report saying it’s possible to see thousands of terns passing through in one day.  In winter 2019 we had sightings of birds ringed at Cemlyn in June 2019 from this region.  The small orange flags used are visible with a telescope.

Sandwich terns tend to stay south for the first few years of their life until they are ready to breed, so it is unlikely that we will see the birds ringed at Cemlyn until 2021. We had one report of a sighting of these ringed birds as far south as South Africa which is a little unusual in their first year.

The re-tern (!!) journey continues onwards to Morocco, at which point some may head east to the Mediterranean and even cross land and travel to colonies in the Netherlands and Denmark. Some sightings in April 2020 have been of birds ringed here. Others will follow the line due to north to Portugal and then on up to colonies in the UK,

Even after that great journey, Sandwich terns may spend time prospecting different breeding sites, flying between colonies to check them out and see which is most suitable. This can sometimes involve relocating to a few hundred miles away. This may also happen if there is a disturbance such as predation once they’ve already settled. As a result of this, there can be large fluctuations between the breeding colonies during any year. We discovered evidence of such movements at the end of Summer 2019 as birds ringed at Cemlyn were seen along the North Wales coast and up the English coast to Cumbria and even to Scotland.

Although Sandwich tern colonies in the British Isles are few in number, they are densely populated with Sandwich terns. Now as April draws to an end, the Sandwich terns at Cemlyn have made themselves at home, hopefully for the rest of the Summer.  At Cemlyn they share the low lying islands with other terns and a sizeable colony of black headed gulls. We will look at this interesting relationship in a future blog.

Cemlyn is sometimes referred to as the jewel in the crown of Anglesey's Area of Outstanding Natural Beauty.  Its unique shingle ridge, re-sculpted each year by sea and storm, shelters a shallow, brackish lagoon and several islets.  In summer months, these host the only colony of Sandwich terns in Wales, breeding alongside their common and Arctic cousins.  Crucial to the tern colony’s success has been the employment of seasonal wardens.  This has previously been financed by a range of measures, including a very generous subscription from an individual supporter.  Sadly, in 2019, this come to an end – and Cemlyn’s terns now face a very uncertain future. We want to ensure that the terns have a future at Cemlyn.  You can help ensure this  - find out how here,

(This is an expanded version of a post from the Cemlyn wardens facebook page)