Unravelling the foraging behaviour of the world's longest migrant

Abstract

**Abstract:** Arctic terns undertake the longest migration on earth, travelling from their breeding grounds in high latitudes of the northern hemisphere, to the overwintering grounds in Antarctica. This declining species covers distances greater than 90,000 km per year, travels across the planet's vast oceans and encounters more daylight than any other animal. Iceland provides important breeding grounds for arctic terns with 20-30% of the global population returning here annually; during four breeding seasons from 2018 to 2021 we deployed more than 100 biologgers at a large colony. These accelerometers, activity loggers and GPS tracking devices will reveal, with unprecedented accuracy, the flyways used by migrating arctic terns, the locations of key stopover sites, and activities in the Southern Ocean. We will identify the conservation landscape over this epic migration: highlighting areas where human conflict may occur, areas that are protected, and highlight locations that may need protection. The wind conditions that arctic terns encounter will be modelled, and we will determine whether they are using trade winds to aid the migratory flights. Activity loggers will identify how long they spend on the wing, and whether they are foraging on route or flying continuously to known foraging locations. We hypothesise that the migratory routes will be a mixture of those followed by tracked birds from The Netherlands and Greenland. How the routes and behaviours relate to morphology and sex will also be discussed. **Authors:** Joanne Morten¹, Julian Burgos², Lee Collins³, Sara Maxwell⁴, Eliza-Jane Morin⁵, Nicole Parr¹, William Thurston⁶, Freydís Vigfúsdóttir⁷, Matthew Witt¹, Lucy Hawkes¹ ¹University of Exeter, ²Marine and Freshwater Research Institute, ³N/A, ⁴University of Washington, ⁵University of Westfjords, ⁶Met Office, ⁷University of Iceland