Sandwich tern (Thalasseus sandvicensis)

Sandwich tern (Thalasseus sandvicensis) are a large tern, similar in size to black-headed gull (Chroicocephalus ridibundus) but slimmer. Adult breeding plumage consists of pale grey upperparts and white underparts with a black cap and crest on the head. They have short black legs and a narrow beak black beak with a yellow tip (fig. 1) (Svensson et al, 2020). Sandwich tern are colony nesters, typically on dry ground such as shingle or sandy beaches. Their diet consists of small fish such as sandeel, herring, and sprat. Sandwich tern typically live to around 12 years old, breeding at 3 years (Harris et al, 2024). 

Population & Distribution:
Sandwich terns are a common summer visitor to the East Grampian Coast, with large numbers breeding at Forvie National Nature Reserve (NNR). Around 9% of the global sandwich tern breeding population is hosted by Britain and Ireland, with around 7% of this population found in Scotland (fig. 2 ) (Burnell et al, 2023; Harris et al, 2024). Over the years sandwich tern have been recorded breeding in two key areas along the East Grampian Coast: Forvie NNR and RSPB Loch of Strathbeg (fig. 3 & 4). However, there have been no breeding records at Strathbeg since 2000 when the breeding colony area was flooded. Forvie NNR is a stronghold for the species along the East Grampian Coast (fig. 5), although numbers do fluctuate annually.

Conservation Status:
Sandwich tern are an Amber listed species due to a moderate breeding range decline over at least 25 years and their breeding localisation (Stanbury et al, 2024)

Factors Impacting Sandwich Tern:
As they nest on the ground, sandwich tern chicks and eggs are particularly vulnerable to predation from red fox (Vulpes vulpes), badger (Meles meles) and otter (Lutra lutra) (Harris et al, 2024). At Forvie NNR, electric fencing is erected every breeding season to protect the colony from predators such as these. 

Sandwich tern are vulnerable to climate change impacts, for example rising sea temperatures changing distribution and abundance of prey species. 

Highly Pathogenic Avian Influenza (HPAI) has impacted sandwich terns both locally and nationally, with high mortality rates recorded. Across the UK, a 35% decline in the sandwich tern population was found when compared to pre-HPAI baseline counts  (Harris et al, 2024; Tremlett et al, 2024).. HPAI impacted the Forvie NNR breeding population of sandwich tern, with over 200 dead fledglings in 2023. However, the adult mortality rates were low and so it is believed these birds will return to Forvie to breed in subsequent years (Short, 2023). 

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