A weather surveillance radar view of Alaskan avian migration

Abstract

Monitoring avian migration within subarctic regions of the globe poses logistical challenges. Populations in these regions often encounter the most rapid effects of changing climates, and these seasonally productive areas are especially important in supporting bird populations—emphasizing the need for monitoring tools and strategies. To this end, we leverage the untapped potential of weather surveillance radar data to quantify active migration through the airspaces of Alaska. We use over 400 000 NEXRAD radar scans from seven stations across the state between 1995 and 2018 (86% of samples derived from 2013 to 2018) to measure spring and autumn migration intensity, phenology and directionality. A large bow-shaped terrestrial migratory system spanning the southern two-thirds of the state was identified, with birds generally moving along a northwest–southeast diagonal axis east of the 150th meridian, and along a northeast–southwest axis west of this meridian. Spring peak migration ranged from 3 May to 30 May and between, 18 August and 12 September during the autumn, with timing across stations predicted by longitude, rather than latitude. Across all stations, the intensity of migration was greatest during the autumn as compared to spring, highlighting the opportunity to measure seasonal indices of net breeding productivity for this important system as additional years of radar measurements are amassed.

The first documentation of the Nearctic–Paleotropical migratory route of the Arctic Warbler

“…Despite recent research detecting cryptic species in the clade (Alstrӧm et al, 2011 ), information on Arctic Warbler breeding and movement ecology in North America is scarce (Kessel, 1989 ; Lowther & Sharbough, 2020 ). Alaskan migratory strategies are bifurcated around the 150th meridian, with western Alaskan birds often taking western migratory routes (Sivakumar et al, 2021 ); Arctic Warblers fall into this group as they fly a southwestern route to wintering grounds in Southeast Asia. Little is known about their passage in either geography or timing (Alerstam et al, 2008 ; Kessel, 1989 ; Lowther & Sharbough, 2020 ), despite the route providing a mechanism for the transcontinental spread of avian influenza (Winker et al, 2007 ) and Arctic Warblers being a high‐priority study species (Pearce & Ramey, 2006 ).…”

“…Despite recent research detecting cryptic species in the clade (Alstrӧm et al, 2011), information on Arctic Warbler breeding and movement ecology in North America is scarce (Kessel, 1989;Lowther & Sharbough, 2020). Alaskan migratory strategies are bifurcated around the 150th meridian, with western Alaskan birds often taking western migratory routes (Sivakumar et al, 2021); Arctic Warblers fall into this group as they fly a southwestern route to wintering grounds in Southeast Asia.Little is known about their passage in either geography or timing…”

An ecological risk assessment for the impacts of offshore wind farms on birds in Australia

“…Observations of avoidance behaviour, using a combination of radar and camera observations, with consistent survey methods, can provide data to examine taxon‐specific changes at a site before and after construction, and allow comparisons with control sites (Skov et al, 2012). Weather radars have been used to track the departure of migratory shorebirds and the migration routes of land birds (Lane & Jessop, 1985; Sivakumar et al, 2021; Tulp et al, 1994; Walsh et al, 2017; Weisshaupt et al, 2018). The existing network of these weather radar stations around Australia provides a potential resource for tracking birds around Australia's coastline, including across Bass and Torres Straits.…”

Long-term changes in the timing of autumn migration in Alaska’s boreal songbirds

“…We used more than 20 years of autumn migration data from two passerine banding stations (Figure 1), located 277 km apart along the same major migratory flyway in eastern Interior Alaska, the Tanana River Valley (Cooper and Ritchie 1995, Sivakumar et al 2021). The valley is a well-documented bird migration corridor (Kessel 1984, McIntyre and Ambrose 1999, Benson and Winker 2001) and, for this reason, the Upper River Tanana Valley is recognized as a Global Important Bird Area (Smith et al 2014, BirdLife International 2023).…”