This is the most marine of the tern species foraging in deeper waters. It feeds on shoals of sandeel and herring among others. Breeding sites are almost exclusively on predator-free islands and islets in association with colonies of other coastal birds, e.g. Black-headed gull (Chroicocephalus ridibundus). Its occurrence is unstable and it may move several 100 kilometers from year to year without any obvious reason. Breeding colonies are often larger than other tern species and may amount to more than 1000 pairs.
The Sandwich tern is listed on Annex I of the Birds Directive (Directive 2009/147/EC).