Black-capped Vireo Post-delisting Monitoring Interim Report December 2024

The Endangered Species Act (ESA) requires the U.S. Fish and Wildlife Service (Service) to monitor the status of all species that are delisted due to recovery, in cooperation with the States, for no less than five years. This process, known as post-delisting monitoring, is meant to ensure the species continues its healthy status following the removal of ESA protections. The Post-delisting Monitoring Plan (PDMP) for the black-capped vireo (Vireo atricapilla) was developed by the Service along with our partners to provide a process to monitor the status of the species until the year 2030.

This interim report represents the halfway point of the PDMP and provides data and information collected by the Service and our partners to evaluate the species’ status. We are pleased to report that the black-capped vireo continues to thrive in greater numbers than was known at the time it was delisted in 2018. Of note in this interim report is the data from major populations, which continue to show strong abundance numbers and low brown-headed cowbird parasitism rates. Additionally, six large populations have been reported that were previously not included in the 2016 Species Status Assessment (Salt Canyon, Broadheart Preserve, Government Canyon State Natural Area, McGillivray and Leona McKie Muse Wildlife Management Area and two Texas Department of Transportation road transects) and three properties originally reported with small populations in the SSA, now show substantial numbers of vireos (Bandera Corridor Conservation Bank, Balcones Canyonlands Preserve, and Possum Kingdom State Park). Not all locations showed increases; a few properties reported fewer numbers than previously documented, for reasons not currently understood (South Llano River State Park and Devil’s Sinkhole State Natural Area). Residual threats to the species still exist; however, it appears that the magnitude of these threats continues to decline or is managed. Continuing to track these threats as well as employ management techniques for habitat and species management (e.g., cowbird control, prescribed fire) is still important for the black-capped vireo.

There are many factors that have led to the success story of the black-capped vireo. Of primary importance are the numerous research projects that resulted in practices to manage stressors on the species and its habitat. The Service’s first report on the status of the vireo was completed in 1985, which led to its listing as endangered in 1987. At that time, approximately 300 birds could be accounted for across the entire breeding range and the largest known population was about 50 pairs in the Austin, Texas area. Additionally, the population at Fort Cavazos (then named Fort Hood) was almost non-existent, with only a couple of males reportedly passing through. Today, the Austin area is estimated to have over 400 pairs and Fort Cavazos over 9,000. These large populations resulted from efforts to improve and expand available habitat and to increase reproductive success through the control of brown-headed cowbirds. Additionally, the creation of the Balcones Canyonlands National Wildlife Refuge and the Balcones Canyonlands Preserve greatly facilitated these efforts in the Austin area where habitat would otherwise have been permanently lost to development.

During the post-delisting monitoring period, our partners put forth an outstanding effort to ensure we continued to track the species’ status within the U.S. portion of the range. We employed the use of citizen science as a trial for small public lands populations; we conducted a pilot project using automated recording units to detect singing males, and we utilized rural highways as a means for conducting transect point counts in the heart of the range. These and other stories can be found in the annual post-delisting monitoring newsletters at: https://www.fws.gov/library/collections/black-capped-vireo-post-delisting-newsletters.

Based on the information we have received thus far, we believe the black-capped vireo is stable to increasing following its delisting, and no thresholds have been reached that need to be addressed through an active response. Our recommendation moving forward is to continue the strong effort of monitoring the species at the same or greater level in the second half of the postdelisting monitoring period. We are extremely grateful to all our partners who have greatly contributed to the effort of monitoring, management, and reporting information included in this interim report.