Author: Elva Manquera

A new research paper published in the journal Avian Conservation and Ecology by partners Bob Altman and Joel Geier and KBO scientist Sarah Rockwell presents the first estimates of post-fledging survival and site persistence of the Oregon Vesper Sparrow. The authors used mark-resight methodology, a method involving color-banding birds and observing them in the wild, to track the survival of fledglings in the weeks after they left their nests in the Willamette Valley of Oregon. The authors found that their survival estimates, derived from mark-resighting, were substantially higher than those found in previous studies using radio-tracking in other grassland songbirds. Post-fledging survival of Oregon Vesper Sparrows in the Willamette Valley was the highest ever reported for similarly sized grassland birds – 62.9% for the first nine weeks out of the nest, typically the most vulnerable time in a bird’s life. These differences may be due to either the naturally high survival of this subspecies in this region or a negative impact of radio-tracking on birds, particularly on fledglings, including entanglement and increased predation risk.

The paper concludes by acknowledging the greater effort needed for mark-resight methodology, but recommending it when possible as a less invasive and potentially more accurate alternative to radio-tracking for studying post-fledging survival in grassland birds, especially species of conservation concern. Post-fledging and juvenile survival are important pieces of information to estimate the population growth rate and extinction risk for this subspecies. The Oregon Vesper Sparrow is currently under review for listing as federally threatened or endangered, and the results presented in this paper will help the USFWS make this decision.

This study is a part of range-wide research on the imperiled Oregon Vesper Sparrow that KBO is conducting with the above-mentioned partners in the Willamette Valley, OR, and Ecostudies Institute in the Puget Lowlands, WA. Juvenile return rates at KBO’s field site on Howard Prairie are nowhere near as high as in the Willamette Valley – but this doesn’t necessarily mean that mortality is higher. It could mean that our young birds are more likely to disperse to other meadows than return to our study site. This is an important question in understanding the demography and possible causes of population decline in this subspecies and is an active area of research.

The study was funded primarily by the Oregon Department of Fish and Wildlife, with additional support from the American Bird Conservancy, U.S. Fish and Wildlife Service Multi-State State Wildlife Grant Program, U.S. Fish and Wildlife Service Migratory Birds Program, Oregon Wildlife Foundation, Wildlife Forever Fund, and Greenbelt Land Trust.

Citation:
Altman, B., J. Geier, and S. M. Rockwell. 2024. High post-fledging survival and site persistence using mark-resight methodology for Oregon Vesper Sparrows in the Willamette Valley, Oregon. Avian Conservation and Ecology 19(2):8. https://doi.org/10.5751/ACE-02706-190208

You can read the full article here: https://ace-eco.org/vol19/iss2/art8/