Use of sea ice by arctic terns Sterna paradisaea in Antarctica and impacts of climate change.

Arctic terns spend their breeding and non‐breeding seasons in polar environments at opposite ends of the world. The sensitivity of polar regions to climate change makes it essential to understand the ecology of arctic terns but the remoteness of the Antarctic presents a considerable challenge. One solution is to use 'biologgers' to monitor remotely their behaviour and distribution in the Antarctic. Data from birds tagged with light‐level global location sensors (geolocators) in 2015 and 2017 showed that a third of their annual cycle was spent amongst Antarctic sea ice. After reaching the East Antarctic in the austral spring, they gradually moved west, foraging in fragmented ice zones of the Antarctic coastline, leaving in the austral autumn for their return northward migration via the Atlantic. Changes in patterns of movement between phases of 24‐h daylight and diel day/night conditions were likely linked to the annual moult, and stable isotope analyses suggest that krill (Euphausia species) was an important component of their diet. There were marked differences in movement behaviour between arctic terns tagged in 2015 compared to 2017 that may relate to unusual changes in sea‐ice extent. The arctic tern may be unique amongst seabirds that utilise the Antarctic environment in summer in being able to move widely without nesting constraints, and may present a means of characterising the effects of climate change on species dependent for foraging on Antarctic sea‐ice and krill. [ABSTRACT FROM AUTHOR]