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

SAGU_Argos_locations contains locations of the SAGU tagged with Lotek Argos PinPoint 75 tags. The locations were all PTT locations, no GPS locations were transmitted. Points generated with unsuccessful satellite fix were excluded. We only used PTT locations derived from > 4 satellite transmissions (i.e., location classes 0, 1, 2, and 3; Douglas *et al.* 2012).

## Description of the data and file structure

SAGU_Argos_locations.CSV: This the PTT data. Has 12 columns \"Platform ID No.\" = id of transmitter, \"Platform\" is blank, \"Prg No\" is just the project name, \"Pass dur. (s)\" = the seconds the satellite pass took, \"Msg date\" = date location was transmitted, \"Sat.\" =Satellite id, \"alarm\", \"Format name\". were included by ARGOS but are not useful, \"loc. date\" = date of the locations, \"Longitude\" and \"Latitude\" are longitude and latitude, \"Loc. quality\" is the location class.

SAGU_calibration_data...