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

Abstract

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.

Seasonally specific responses to wind patterns and ocean productivity facilitate the longest animal migration on Earth

“…Terns from our study site on average departed from Svalbard on 3 September, which is from 1 to 2 mo later than previously shown in studies from more southerly breeding areas (Table S1; Egevang et al 2010, Fijn et al 2013, Loring et al 2017, Volkov et al 2017, Alerstam et al 2019, Redfern & Bevan 2020a. The late departure date of our tracked individuals corresponds with later departure of other species from northern latitudes (Butler et al 1998, Gilg et al 2013, Davis et al 2016.…”

“…As a general pattern, migratory birds breeding at higher latitudes depart from their breeding areas later than their southern conspecifics, owing to the later onset of the breeding season at high latitudes (Conklin et al 2010, Briedis et al 2016. Similarly, our tracked terns arrived at the breeding sites later than their conspecifics breeding at more southern latitudes (Egevang et al 2010, Fijn et al 2013, Loring et al 2017, Volkov et al 2017, Alerstam et al 2019, Redfern & Bevan 2020a. Such population-level differences in migration timing can lead to significant variation in migration strategies, as different populations face different environmental conditions en route (González-Solís et al 2009, Sittler et al 2011, Hanssen et al 2016).…”

“…Breeding populations from lower latitudes arrive in Antarctica relatively earlier and often over-winter further east in the Indian Ocean (e.g. Alerstam et al 2019, Redfern & Bevan 2020b.…”

Global Connectivity of Southern Ocean Ecosystems

“…Short-tailed shearwaters Ardenna tenuirostris tracked from Tasmania moved into the Southern Ocean after breeding, before flying north across the western Pacific Ocean to waters near Japan or further north in the Bering Sea (Carey et al, 2014). The classic example of a long-distance seabird migrant is the Arctic tern Sterna paradisaea, which breeds in Europe and the Arctic, then migrates in its non-breeding season to the Antarctic where it feeds in sea ice environments, thereby experiencing an endless summer (Egevang et al, 2010;Redfern and Bevan, 2020).…”

Pair bonds during the annual cycle of a long-distance migrant, the Arctic Tern (Sterna paradisaea)

“…The question whether or not breeding partners stay together for part or all of the post-breeding migration and wintering period has also been raised for Arctic Terns (Busse 1983) which migrate from high northernlatitude breeding colonies to non-breeding areas in the Antarctic and have one of the longest migrations of any species (Egevang et al 2010;Fijn et al 2013;Redfern and Bevan 2020a). The geographic scale of this migration provides an opportunity for an unambiguous test of partner association for a colonial seabird throughout the annual cycle.…”