Raptor Research Foundation

New from the Journal of Raptor Research

Citizen Science Data Reveal that Nigerian Hooded Vulture Declines are Likely Driven by Climatic Factors Rather than Limited Habitat

https://bioone.org/journals/journal-of-raptor-research/volume-60/issue-3/jrr2541/Citizen-Science-Data-Reveal-That-Nigerian-Hooded-Vulture-Declines-are/10.3356/jrr2541.full

Caption for all three figures: Hooded Vultures (Necrosyrtes monachus) foraging close to a human settlement.
Photo credit: Joseph K. Afrifa.

Vultures on the Rise: New Study Provides Evidence of Population Increase and Delayed Migration in Western North America
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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.

Dönnecke et al. (2026)

Read full paper at https://rapt.kglmeridian.com/view/journals/rapt/60/2/article-p1_5.xml

Photo: Part of a kettle of Turkey Vultures soaring above Rocky Point, Vancouver Island, British Columbia Canada. Photo Daniel Dönnecke. Credit Daniel Dönnecke.

Batty Behavior: Falcon Seen Feasting on Atypical Prey Species in Greece
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Falcons are lauded for their speed and agility. The Eurasian Hobby (Falco subbuteo), skilled at snagging birds and insects out of the air, is no exception. However, during twilight on one fateful day in October, researcher Apostolos Christopoulos observed several hobbies feeding on something else in a protected wetland in Greece — bats from the genus Pipistrelus. Bat predation by Eurasian Hobbies has only been recorded a handful of times before and the species is relatively unstudied, making this discovery an illuminating one. Migration is an energetically demanding time of year for all raptors and understanding which prey items feature in a species’ refueling strategy can have strong conservation implications. This observation suggests that bats may offer critical caloric support for migrating hobbies, especially in wetland-urban habitats.

Eurasian Hobbies undertake impressive migrations each year, flying from Palearctic breeding grounds to Africa, the Indian Subcontinent, and Southeastern Asia. To complete these journeys, they must find places to refuel and rest, called “stopover sites.” Wetlands like the Messolonghi-Aitoliko lagoons of Southwestern Greece, where this predation event was observed, offer especially attractive stopover habitat for migrating raptors because they host a diversity of prey. These specific lagoons also offer a final opportunity for migratory birds to consume prey before flying across the Mediterranean Sea on their way to Africa.

Christopoulos, with the Department of Biology at the University of Athens, Greece, recently published his observation in the Journal of Raptor Research under the title “Bat Predation at Twilight by Migrating Eurasian Hobbies Falco subbuteo in a Major Mediterranean Lagoon.” Here he describes an observation of one particular hobby dispatching eight bats in a half hour on October 12th, 2025, identified by a distinctive protruding tail feather and confirmed as a juvenile. “This observation represents a predation event recorded at a scale that has never been documented before in Greece,” says Christopoulos. “Many people may not realize how strongly these birds depend on specific key locations and on the presence of stable local prey populations,” says Christopoulos. “By documenting this behavior, we demonstrate that conserving local prey populations, through the protection of the habitats in which they live, is essential for the survival of migratory raptors.”

Raptors are top predators. As such, they exert a notable influence on ecosystem dynamics and can serve as sentinels of environmental health, or lack thereof. Christopoulos hopes that his observation will inspire future focus on the relationship between environmental change and selection of stopover by migratory raptors of various age classes, as well as more detailed investigation into which prey items are favored at critical geographical junctures.

Christopoulos, Apostolos (2026).
Read full paper at https://rapt.kglmeridian.com/view/journals/rapt/60/2/article-p1_17.xml
Photo: A juvenile Eurasian Hobby
Credit Apostolos Christopoulos

Girl Power: Hawk Parents Invest More in Female Offspring
PRESS RELEASE

Few among us appreciate being called cheap, yet this term has a useful application in bird world. A new study published in the Journal of Raptor Research, “Factors Influencing Nestling S*x Ratios of Suburban and Rural Red-Shouldered Hawks, 2004-2016,” finds that male Red-shouldered Hawks (Buteo lineatus) are the cheaper of the s*xes, meaning hawk parents prioritize producing female offspring when conditions are optimal. This means that higher quality territories could result in more females, offering biologists clues about habitat health, which is important intel as the species adapts to urban environments with increasing frequency.

Red-shouldered Hawks are medium-sized generalist raptors inhabiting forested, suburban, and urban habitats. Females are roughly 25% heavier than males and can be s*xed in the nest after three weeks of age based on measurements of their legs and feet. Like other raptors, Red-shouldered Hawks can adjust the s*x ratios of their offspring prior to hatch which can lead to investment in the more “valuable” s*x during times of plenty. Raptor biologists theorize that since females can begin breeding earlier than males, it could be advantageous for parents to invest in female chicks because they will begin contributing genes to the population sooner than males. In other words, females get a head start. Additionally, producing the larger, more energetically demanding females may simply be too difficult when resources are scarce.

Lead author Cheryl Dykstra has been studying Red-shouldered Hawks in Ohio for 30 years. Her team has amassed a robust dataset on various realms of this species’ ecology, and they have worked with multiple stakeholders to gain research access to hawk populations in rural, suburban, and urban environments. Her team set out to determine whether there is a relationship between higher quality territories, meaning they contain more prey, and the proportion of female versus male nestlings. They found that higher quality territories indeed yielded more female nestlings, confirming previous research on other raptor species such as the Eleonora’s Falcon (Falco eleonorae), and Lesser Kestrels (Falco naumanni), among others. They also found a correlation between brood size, hatch date, and s*x ratio in the nest: Solitary young are more likely to be female than male, and the probability of an egg hatching into a male increased for eggs laid later in the season regardless of habitat quality.

The urban Red-shouldered Hawks featured in this study encounter different threats than their forest-dwelling counterparts, an important consideration when developing species-wide protection plans. In the future, the team hopes to investigate, for example, whether urban Red-shouldered Hawks are exposed to rodenticide since they occasionally feed on rats. “We also think it is likely that urban birds experience more collisions with vehicles than rural birds, with effects on mortality and turnover rates,” say Dykstra. Her team wants to continue involving the public in activities like banding nestlings to help increase public awareness of the importance of the hawks in their area. “The relationship between humans and urban-adapting birds is critical for conservation,” she says, “and few people can resist the appeal of an awkward, half-feathered nestling raptor.” Top predators are important members of any ecosystem, yet their contributions often fly under the radar. Projects like this not only answer pertinent questions about the species’ biology but also help increase collective appreciation of raptors.

Dykstra et al. (2026)
Read full paper at https://rapt.kglmeridian.com/view/journals/rapt/60/2/article-p1_7.xml

Photo: Nestling red-shouldered hawks in suburban Cincinnati, Ohio.
Credit Cheryl Dykstra.