Geolocator Deployment and Recovery
From 2016 to 2019, we captured adult male Arctic Warblers using mist nets with decoys and playback of conspecific songs and alarm calls. We banded each bird with a USGS aluminum leg band, sexed and aged them (Pyle 1997), measured their mass with a digital scale (±0.01g), and took standard morphological measurements. We also collected incidentally shed feathers in 2017 and feather and blood samples from 10 birds for contaminant analysis in 2018 (Stenhouse et al. 2019). In 2016, we attached 0.4 g archival light-level geolocators (Lotek ML6040; Wareham, UK) to 27 after-second-year (adult) males. In 2018, we attached 0.3 g geolocators (Intigeo tags, Migrate Tech, Cambridge, UK) to 15 adult males. In both years, we attached geolocators to birds using a modified Rappole-Tipton harness (Rappole & Tipton 1991; Streby et al.2015) constructed of 0.5 mm black stretch jewelry cord. We assessed and adjusted the harness fit before release. Geolocator mass was approximately 3–4% of the body mass of each bird. All geolocators were deployed on presumed breeding territories in Denali National Park and Preserve, Alaska (63.49° N, 150.07° W) from early June to early July, with most (33 of 42) deployed within a 101-ha study area.
Initially, we attempted to recapture tagged birds using the same capture methods at the initial capture sites from early June to early July in subsequent years (2017-2019). When tagged birds were not sighted or recaptured at these sites, we expanded our recapture efforts to suitable breeding habitat (i.e., tall shrubs in riparian zones) within 500 m of initial capture sites. Upon recapturing tagged birds, we recorded their band number, removed the geolocator, measured the bird, and released it. The data were then downloaded and readied for processing.