Migratory and winter movements of Arctic Alaska breeding Sabine’s Gulls (Xema sabini)

The Sabine’s Gull (Xema sabini) is a pelagic, Arctic-breeding species with a circumpolar breeding distribution. Little is known about migration routes for Sabine’s Gulls breeding in the Alaskan Arctic. We tagged Sabine’s Gulls on their northern Alaska breeding grounds to identify migration routes and wintering areas and compare geolocators and GPS pinpoint tags for use on small-bodied gulls. Twelve geolocators were deployed in northern Alaska in 2011 (Colville River Delta) of which four were recovered, and five GPS pinpoint tags in 2021 (Qupaluk). Although the GPS pinpoint tags provided more accurate locations allowing for finer-scale habitat evaluation, and did not require recapture of birds, the overall coverage provided by geolocators was superior in this study given the constraints of the number of locations GPS pinpoint tags can record. Broadly, the four (one tag failed) tracked Sabine’s Gulls migrated away from the breeding grounds as expected, passing along the west coast of Alaska and south along the west coast of the Americas to winter in the Humboldt Current off the coast of Peru. Our tracked gulls used the same migratory staging and wintering areas as did Sabine’s Gulls breeding in the Canadian Arctic (Davis et al., 2016). Such reliance on specific marine areas presents risks from climate-related changes or ecological damage to those areas.

Methods
We deployed Mk12 (British Antarctic Survey) light-level geolocators (<1g) at two sites in northern Alaska; the Colville River Delta (Anachlik Island; 70°23’N, 151°29’W), and northeast of Teshekpuk Lake (Qupaluk; 70°40’N, 152°43’W). In the summer of 2011, we captured 12 adult Sabine’s Gulls on Anachlik Island (the site of a homestead), using either a whoosh net or cage trap placed at a feeding station, and tagged them with Mk12 (British Antarctic Survey) light-level geolocators (<1g). In the summer of 2021, we captured five adult Sabine’s Gulls on their nests with a bownet at Qupaluk (remote area with no permanent human presence) and equipped them with 4g Lotek Argos PinPoint 75 tags using leg-loop harnesses with 1.9mm Teflon ribbon, and copper crimps (< 0.03 % of total body weight). Tags were programmed to take a GPS point every two days from 15 August to 15 November, and then one point every five days until the batteries died.