Near-absence of high pathogenicity avian influenza (HPAI) in Little Terns <i>Sternula albifrons</i> across 13 European countries

Capsule: Our survey of site managers or researchers for all Little Tern colonies in 13 European countries found only three cases of dead birds proven to have succumbed to high pathogenicity avian influenza (HPAI) in 2022–2023, amongst tens of thousands of breeding birds. Aims: In view of few reported cases of HPAI in Little Terns, despite the high prevalence among other seabirds, especially the four maritime terns (Common Tern Sterna hirundo, Arctic Tern S. paradiseaea, Roseate Tern S. dougallii and Sandwich Tern Thalasseus sandvicensis), we explored whether this was a genuine difference. Methods: We devised a brief survey asking simple questions about HPAI found in any dead adult Little Terns, and emailed it to every known site manager or colony recorder in Britain, the Isle of Man and Ireland. For countries in mainland Europe with significant populations of Little Terns, we sent the same survey to ornithologists identified through their involvement in monitoring the species, or leadership of their country's contribution to the recent Second European Breeding Bird Atlas. Results: For Ireland, Scotland, England, Wales and the Isle of Man, we achieved significant coverage; out of the nine Little Terns that were tested across Europe, only three dead individuals in England and Ireland were recorded as testing positive for HPAI. Across the coastal colonies in mainland Europe, none were recorded. Conclusions: HPAI was very scarce, or absent, in 2022 or 2023 in all observed colonies of Little Terns in Europe. There is no firm evidence for why most Little Terns, almost alone among above-ground nesting and colonial seabirds, avoided catching or succumbing to HPAI, but we discuss likely reasons and conclude that their spacing between nests and (unlike the other marine tern species) their tendency to avoid other terns and gulls, means there were few opportunities for spreading the virus.