KBO tracks the first Oregon Vesper Sparrows!
Written by Dr. Sarah Rockwell
The unique Oregon subspecies of Vesper Sparrow, roughly estimated at just 2,000 birds, is of conservation concern. It is currently under review for listing under the Endangered Species Act because of its small population size and declining trend. One of the biggest challenges in identifying ways to help migratory species is the fact that we don’t know where they are for most of the year. Vesper Sparrows breeding in Oregon are only here for about half the year, from mid-April to early October. Because different subspecies of Vesper Sparrow mix on the wintering grounds in California and are not visually distinguishable, until now, we only had a rough idea of where Oregon Vesper Sparrows spend the non-breeding months. This study will help answer questions essential for future conservation efforts – where are these birds going during migration and winter, and what challenges might they face there?
To address this critical knowledge gap, we expanded KBO’s ongoing Oregon Vesper Sparrow research to include using miniaturized archival GPS tags to track the migration of sparrows breeding in the Rogue Basin. In 2020, we captured 10 males via target-netting at our Lily Glen study site, color-banded them, and deployed GPS tags using a leg-loop harness attachment (for more details and photos of this process, see here ). In 2021, we located and recaptured four of these birds to retrieve tags and stored data. Three of the tags successfully recorded these individuals’ fall migration and/or wintering locations; one also contained the spring migration track!
Non-breeding season movements have never been tracked in this subspecies before, and results from these first three birds are incredibly interesting in their variation. You may have already followed the adventures of Po, Gram, and Affy in our recent series of Facebook posts, where we learned where they traveled during migration, but we will recap the highlights here and below in a video. One male (Po; in green) departed Lily Glen on Sept 19 on what appears to be a “false start” migration attempt – he spent one night about 25 km southwest of Tule Lake and then headed right back to Lily Glen – a behavior that we hadn’t recorded before, and in fact, would have been nearly impossible to observe without the GPS tag data. He left Lily Glen again on Sept 24 and sped down to his wintering grounds in just two days. This was also the only individual for whom we also captured spring migration – Po left his overwintering area on the evening of Apr 9, made two short stopovers just east of Vina, CA, and Redding, CA, and was back setting up his territory at Lily Glen by Apr 15.
Another male (Gram, in blue) left Lily Glen on Sept 19 and spent two weeks on an extended fall stopover outside of Chico, CA, before arriving at his wintering grounds in October. A third male (Affy; in pink) chose a more westerly route and had multiple short fall stopovers, including at Sutter Butte, an interesting geological formation made of eroded volcanic lava domes outside of Yuba City that provides a habitat island in the highly developed Central Valley. Unfortunately, Affy’s GPS tag stopped functioning mid-October, so we do not know his final wintering location. The two birds we have wintering locations for (Po and Gram) spent the winter near Raymond, CA, and El Rancho, CA, in what appears to be oak savannah habitat in the western foothills of the Sierra Nevada.
This study is the first to identify precise migratory stopover sites and overwintering areas used by this imperiled subspecies, and it addresses a critical information gap for future conservation efforts. So far, it seems like the Oregon Vesper Sparrows are using grassland and oak savannah habitat in the foothills east and west of the Central Valley as a stopover and overwintering habitat and avoiding the heavily agricultural Central Valley. We retrieved additional GPS tags in 2023, and after analyzing the data, we will use this information to assess whether conservation actions are warranted at non-breeding sites.
The Bureau of Land Management, Carpenter Foundation, Oregon Conservation and Recreation Fund, and Oregon Wildlife Foundation supported this GPS-tracking work.
Video: https://youtu.be/wKNi96ffKAY
Cover photo: Oregon Vesper Sparrow (c) Frank Lospalluto
