KBO tracks the first Western Purple Martin with GPS tag technology
By Sarah Rockwell
Spoiler alert: Our first recaptured Martin flew almost 8,000 miles to southeastern Brazil and back again!
The unique western subspecies of Purple Martin is of conservation concern, roughly estimated at just 3,500 pairs. Relatively little is known about the Western Purple Martin compared to the more abundant eastern subspecies. One of the biggest challenges in identifying ways to help migratory species is that we simply don’t know where they are most of the year. Western Purple Martins breeding in Oregon are only here from about April to August, and until recently, we only had the slightest idea of where they spend the non-breeding months. From 2020-2023, a small team of researchers from KBO, USFS, USGS, and Cape Arago Audubon Society captured adult Western Purple Martins and outfitted them with lightweight archival GPS tags that fit like a backpack with two leg loops to track their movements. Our goal is to track martins that nest in Oregon to discover their migratory pathways and winter roost locations and assess whether conservation actions are needed at these non-breeding sites. This is the first study of its kind with the western subspecies and the first to track them with GPS technology throughout the year!
There is one important catch – to have a battery small and lightweight enough for a small songbird to carry safely, the tags cannot transmit GPS data, only store it on board. Returning tagged birds must be recaptured following a year-long round-trip migration to retrieve the tag and its precious geospatial data. It can be very challenging to find these birds again, not to mention recapture them! So, we were thrilled to recapture our first female, whom we nicknamed Roxa (‘purple’ in Brazilian Portuguese – pronounced more like “hosha”), in the summer of 2021.
Roxa returned with fascinating information, revealing new discoveries about her incredible 8,000-mile journey. After she left her nesting area in coastal Oregon in August, Roxa first headed south to Baja California, where she spent about a month from mid-Aug to mid-Sept on an extended fall stopover – although somewhat unusual for a songbird, this long pause was not totally unexpected, as it matched hints from earlier research using geolocators on a few martins from British Columbia (Fraser et al. 2017). She then continued south through western Mexico, with GPS points taken every 5 days, including stops in Nicaragua, Costa Rica, Colombia, and Venezuela before entering Brazil, where she passed over many of her Eastern Purple Martin cousins in their wintering area in the Amazon. She then spent another multi-week stopover in late November in northern Minas Gerais, near Parque Nacional do Peruaçu – which was unexpected! Roxa finally completed the last leg of her trip to the southeastern Brazilian coast, where she spent Christmas in Linhares in the state of Espírito Santo. She even made it to the beach city of Praia do Morro in time for Carnaval before winging her way back north and graciously returning her GPS tag to us.
We now have an amazing window into what Roxa and other Western Purple Martins are up to after they leave Oregon and the incredible voyages they undertake. These insights also lead us to more questions. Why does she stop for so long in Baja California Sur, Mexico, and Minas Gerais, Brazil? Could she be molting and regrowing feathers at one of these locations where the insect food resources are especially abundant? Does she use the same route every year, and do other Western Purple Martins use similar or different routes? What changes are occurring in the habitats she occupies along the way? Are any of these places threatened by deforestation, pesticide use, or other conservation challenges? We hope to apply what we have learned to help make sure the Western Purple Martin’s migratory journey, connecting people and places across continents, remains a phenomenon we can all marvel at well into the future.
In summer 2023, we recaptured two more returning Purple Martins with new data to add to our understanding of their migration routes and winter homes – we are so excited to process these data and see how they compare to our first recapture! We also deployed 8 more GPS tags on Purple Martins nesting at Fern Ridge Reservoir near Veneta, OR. Those individuals have finished their nests for this summer and will be leaving soon for parts unknown – but a little less unknown than before – so we will also have more chances to add data to this study next summer.
The USFS, USGS, Purple Martin Conservation Association, and the Greenfield Hartline Habitat Conservation Fund supported this work. The research team comprised Sarah Rockwell from KBO, DeAnna Williams of USFS, Joan Hagar of USGS, and Joe Metzler from Cape Arago Audubon Society. Watch the short video On the Wings of Roxa and join her 8,000-mile journey.
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.
The goal of the conservation assessment is to summarize existing information regarding the biology and ecology of the western Purple Martin (Progne subis arboricola), threats to the species, and management considerations, and to provide information to land managers to assist in the formulation of options for management activities. This species remains abundant in the eastern part of its range, but the western subspecies is of concern in Oregon and Washington due to its narrow range, small population size, reductions in available habitat and cavity nesting sites, competition for remaining cavities from non-native bird species (especially European Starlings [Sturnus vulgaris]), and possibly increases in habitat loss on Brazilian wintering grounds and agricultural insecticide use during all portions of the annual cycle. Federal management for this species follows Forest Service (FS) Region 6 Sensitive Species (SS) and/or Oregon/Washington (OR/WA) BLM Special Status Species (SSS) policies.