Introduction
Description of broadscale migratory movements in songbirds has begun using individual tracking (McKinnon and Love 2018), but species with less common migration strategies lack representation in the current state of the science. The Arctic Warbler (Phylloscopus borealis ) is one of a handful of songbirds that make an annual journey from the Old World to the New World (Kessel 1989; Bairlein et al. 2012), and is the only species in the large genus Phylloscopus that breeds in North America (Bairlein et al. 2006). Information on Arctic Warbler breeding and movement ecology in North America is scarce (Kessel 1989; Lowther & Sharbough 2020); in part, because of a recent split from a clade of other similar Phylloscopus warblers that reduced their transcontinental breeding distribution to Alaska (AlstrÓ§met al. 2011). Contrary to most Alaskan birds, Arctic Warblers migrate west to Southeast Asia and back each year like due to their Old World lineage. Little is known about their passage in either geography or timing (Kessel 1989; Alerstam et al. 2008; Lowther & Sharbough 2020), despite the route providing a vector for the transcontinental spread of avian influenza (Winker et al. 2007).
The Arctic Warbler’s conservation status is currently unclear, although it is considered a species of continental stewardship in Alaska (Handelet al. 2021). Like nearly all other migratory songbirds that nest in Alaska, the Arctic Warbler spends only a small portion of its annual cycle at the breeding grounds (approximately June through August). Moreover, movements and connectivity across the full annual cycle can be a critical driver of speciation and further complicate conservation activities (Webster & Marra 2005). Thus, effective conservation efforts require knowledge of space and resource use during the non-breeding season and an understanding of migratory movement and connectivity (Runge et al. 2014). Using light-level geolocators to track individual movements (Jahn et al. 2013; Deluca et al.2015; Cooper et al. 2017; McKinnon & Love 2018; Tonra et al. 2019), we describe results from the first individual tracking study of Arctic Warblers, including migration behavior, migratory routes, and wintering locations of two individuals.