Vultures on the rise: New study provides evidence of population increase and delayed migration in western North America

Turkey Vultures (Cathartes aura) may not be beautiful, but they are certainly adaptable. A new study published in the Journal of Raptor Research, titled “Turkey Vulture Aggregations at a Water Barrier Provide Evidence of Later Migration and Increasing Population Size over 25 Years” suggests that Turkey Vultures in western North America are increasing in number and delaying their migration departure date. Both findings could be correlated with climate change, although more investigation is needed to confirm. This study presents a new counting method that could prove useful for studying other soaring raptor species, especially at topographical “bottlenecks” like large water crossings.

Turkey Vultures are facultative migrants, meaning some individuals migrate and some do not. The western North American breeding population typically migrates south in the winter with some individuals journeying as far as Venezuela. Being relatively big-bodied, vultures utilize thermals and updrafts to travel efficiently, which funnels their movements along ridges and other landscape features that result in suitable air phenomena. At some junctures, however, they must traverse large bodies of water. At Rocky Point Bird Observatory, located on a military base on the southern tip of Vancouver Island, Canada, researchers recorded “Daily Estimated Totals” or DETs of vultures for 25 years as the birds congregated prior to crossing the 18-kilometer-wide Strait of Juan de Fuca. 

To obtain these DETs, the team paid close attention to what are called kettles — groups of vultures spiraling upwards inside a thermal, so named from a kettle-shaped land formation at one of the first established hawk watch sites. Author on the paper and a long-time volunteer at Rocky Point Bird Observatory, Dr. Daniel Dönnecke, and his team, looked at whether kettle size changed from 1999 through 2023. “Our study indicates that counting raptors in kettles can offer information on population trends, likely with less effort than at hawkwatches,” says Dönnecke, where many raptors are counted singly as they migrate through. “We anticipated that counting kettles would provide useful information on the timing of migration and abundance of the species, but we were surprised to see how strong and clear the pattern was.” 

They found that the annual maximum number of observed Turkey Vultures increased by almost 300% during those 25 years, and the timing of migration shifted to a later start date by 4 days. Population increases in Turkey Vultures have also been recorded through citizen science initiatives such as eBird, Breeding Bird Surveys, and at hawkwatches. “Before our study, there was little recent information for western populations of Turkey Vultures,” says Dönnecke. “To make decisions about conservation effort, it’s important to have up-to-date information about whether the population is increasing, decreasing, or stable.” Dönnecke and his coauthor Dr. Don Kramer hope this study will inspire more collaboration between different types of count sites with the shared goal of investigating shifts in migration timing for various species. They also hope to further investigate the potential correlation between climate change and the associated behavior of migratory birds departing from Vancouver Island. 

Vultures are a relatively understudied and underappreciated raptor, yet they provide a crucial ecosystem service by removing carcasses from the land. Noticing changes to vulture populations early can help ensure that these efficient scavengers remain in the skies. “When members of the public ask why we are counting Turkey Vultures, we find that if we explain their ecological role, their specialized adaptations for soaring, and the reason why kettles form on southern Vancouver Island, people respond with a much more positive view of the species,” says Dönnecke. This study offers a salient reminder that our most common species can act as telltales for environmental change, if we pay attention. 

###

Paper:

Dönnecke et al (2026). Turkey Vulture Aggregations at a Water Barrier Provide Evidence of Later Migration and Increasing Population Size Over 25 Years. Journal of Raptor Research, 60(2):1-11.
DOI: 10.3356/jrr2491

Notes to Editor:

1. The Journal of Raptor Research (JRR) is an international scientific journal dedicated entirely to the dissemination of information about birds of prey. Established in 1967, JRR has published peer-reviewed research on raptor ecology, behavior, life history, conservation, and techniques. JRR is available quarterly to members in electronic and paper format.

2. The Raptor Research Foundation (RRF) is the world’s largest professional society for raptor researchers and conservationists. Founded in 1966 as a non-profit organization, our primary goal is the accumulation and dissemination of scientific information about raptors. The Foundation organizes annual scientific conferences and provides competitive grants & awards for student researchers & conservationists. The Foundation also provides support & networking opportunities for students & early career raptor researchers.