The unique western subspecies of Purple Martin is of conservation concern, roughly estimated at just 3,500 pairs. There is little known about the Western Purple Martins compared to the more abundant eastern subspecies (Rockwell 2019). Previous studies using light-level geolocators have revealed that Eastern Purple Martins largely overwinter in the heavily forested Brazilian Amazon. Still, Western Purple Martins appear to use a different overwintering area in southeastern Brazil, which may be more impacted by agriculture (Fraser et al. 2012). However, these data come from only a small number of individuals breeding in British Columbia that may not represent the entire subspecies. It is unknown whether other western populations, including martins that nest in Oregon, follow the same pattern.
Further, light-level geolocator data have a larger margin of error and are not precise enough to identify specific roosting sites that may need protection (McKinnon and Love 2018). Archival GPS tags provide unprecedented precision in determining these locations. We are using this technology to track migratory routes and overwintering sites used by Western Purple Martins and identify potential conservation opportunities in the non-breeding season. A better understanding of overwintering locations and migratory stopover sites used by Western Purple Martins, as potential threats originating on the non-breeding grounds have been identified in a recent ISSSSP Conservation Assessment as key information gaps needed to target conservation actions (Rockwell 2019).
From 2020-2022, a small team of researchers from KBO, USFS, and USGS captured adult Western Purple Martins breeding in coastal Oregon at night while they roost in their nestboxes. We have captured martins on the Siuslaw National Forest and McKenzie River Trust lands. We band the birds and outfit them with lightweight archival GPS tags that fit like a backpack with two leg loops to track their movements. There’s just one catch – to have a battery small and lightweight enough for a small songbird to carry, the tags cannot transmit data, only store it. Returning tagged birds must be recaptured following a year-long round-trip migration to retrieve the tag and its precious geospatial data. Due to these challenges, most tracking studies of this type have relatively small sample sizes; nevertheless, they have revolutionized our understanding of bird migration. Precise data on the winter whereabouts of a few Western Purple Martin individuals are enormously important compared to the absence of any precise data that we had before this study. Our objectives are to find locations of roost sites used during migration and winter and use this information to identify conservation partners and actions that can be taken during the non-breeding season.
Our first recaptured martin flew almost 7,000 miles to southeastern Brazil and then back again! KBO has joined the International Purple Martin Working Group, which focuses mostly on Eastern Purple Martins, to include our western subspecies in research and conservation activities with partners in more tropical locales. Stay tuned!
This work is supported by the U.S. Forest Service, Purple Martin Conservation Association, and U.S. Geological Survey. Photos provided by Lorelle Sherman.
Fraser, K. C., B. J. M. Stutchbury, C. Silverio, P. M. Kramer, J. Barrow, D. Newstead, N. Mickle, B. F. Cousens, J. C. Lee, D. M. Morrison, T. Shaheen, et al. 2012. Continent-wide tracking to determine migratory connectivity and tropical habitat associations of a declining aerial insectivore. Proceedings of the Royal Society B: Biological Sciences 279:4901–4906.
McKinnon, E. A. and O. P. Love. 2018. Ten years tracking the migrations of small landbirds: Lessons learned in the golden age of bio-logging. The Auk 135:834-856.
Rockwell, S. M. 2019. Conservation Assessment for Purple Martin (Progne subis). Interagency Special Status/Sensitive Species Program Conservation Assessments. USDA Forest Service Region 6 and USDI Bureau of Land Management, Oregon and Washington, 73 p.