Conservation Genetics

, 9:305 | Cite as

Population structure and genetic diversity in Swainson’s Hawks (Buteo swainsoni): implications for conservation

  • Joshua M. Hull
  • Richard Anderson
  • Michael Bradbury
  • James A. Estep
  • Holly B. Ernest
Research Article


Swainson’s Hawks (Buteo swainsoni) are large raptors with a breeding distribution extending across much of western North America where they were historically considered one of the most abundant raptors. Swainson’s Hawks have declined precipitously in many parts of their range during the 20th century, and the historical range in California has been much reduced. In the Central Valley of California (CV), Swainson’s Hawks exhibit behavioral and morphological characteristics apparently different from other regions. To describe the genetic diversity and population structure of Swainson’s Hawks throughout their range, 19 microsatellite loci and 416 base pairs of the mitochondrial control region were analyzed. Microsatellite diversity appears high throughout the contemporary range. A Bayesian model-based analysis of microsatellite genotypes revealed clusters associated with the CV and the Great Basin/Great Plains region of North America (GBGP) with overlap between regions. F ST estimates suggest limited differentiation among Swainson’s Hawks with isolation by distance. A heterozygote excess indicated a recent reduction in effective population size of Swainson’s Hawks across all regions. Control region data revealed no population structure and provided evidence of historic population expansion in the GBGP. In the CV a weaker signature of population expansion was detected, possibly altered by recent declines. While genetic data suggests recent gene-flow across regions, apparent differences between the CV and GBGP in traits with potential fitness consequences (migratory behavior and morphology) along with marked decline in numbers in California call for careful conservation, management, and monitoring of Swainson’s Hawks in the CV.


Swainson’s Hawk Buteo swainsoni Population genetics Mitochondrial DNA Microsatellite 



We would like to thank the Arizona Game and Fish Department, Calgary Wildlife Rehabilitation Society, California Department of Fish and Game, Cascades Raptor Center, Golden Gate Raptor Observatory, HawkWatch International, Laramie Raptor Refuge, Last Chance Forever, Lindsay Wildlife Hospital, Montana Raptor Center, Rocky Mountain Raptor Project, South Plains Refuge, Swainson’s Hawk Technical Advisory Committee, UC Davis Raptor Center, UC Davis Veterinary Teaching Hospital, C Boal, P Bloom, J Papp, B Mattox, J McKinley, J Mulholland, R Murphy, T Bollinger, P Parker, S Blackman, A Disbrow, D Racine, C Briggs, and M Dorin for assistance with sample collection. S Brown, J Eadie, A Hull, T Hull, J Keane, J Kurushima, B May, B Sacks, W Savage, B Stedman, L Tell, J Well, and many others for their technical assistance and advice. Financial support for this project was provided by the Swainson’s Hawk Technical Advisory Committee (via the California Department of Water Resources and the California Department of Fish and Game), the University of California Genetic Resources Conservation Program, the Veterinary Genetics Laboratory at UC Davis, and graduate student funding support through the UC Davis Graduate Group in Ecology. We thank associate editor Stuart Piertney and two anonymous reviewers for their comments on previous versions of this manuscript.


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Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  • Joshua M. Hull
    • 1
  • Richard Anderson
    • 2
  • Michael Bradbury
    • 3
  • James A. Estep
    • 4
  • Holly B. Ernest
    • 1
    • 5
  1. 1.Wildlife and Ecology Unit, Veterinary Genetics LaboratoryUniversity of CaliforniaDavisUSA
  2. 2.DavisUSA
  3. 3.Department of Water ResourcesSacramentoUSA
  4. 4.SacramentoUSA
  5. 5.Department of Population Health and Reproduction, School of Veterinary MedicineUniversity of CaliforniaDavisUSA

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