Caldwell Hahn

USGS Patuxent Wildlife Research Center
12110 Beech Forest Road
Laurel, MD 20708-4015

Telephone: 301-497-5653

Fax: 301-497-5624

Email: chahn@usgs.gov 

Research Wildlife Biologist

Primary Responsibilities: 
We are working on studies at the interface of wildlife disease ecology and human health.  In particular, we are working on several aspects of West Nile Virus as well as theoretical questions of the evolution of immunity.          

The rapid geographic spread of West Nile Virus across the United States has stimulated a wide range of work on transmission and spread of this disease, which is highly pathogenic to both wildlife and people.  We have conducted comparative studies, identifying which avian species are competent reservoirs, maintaining the virus and facilitating its spread by mosquito vectors.  In owls, we also study disease resistance mechanisms by documenting maternal transfer of WNV antibodies in Eastern Screech Owls. Currently we are looking at within-clutch patterns of maternal allocation of WNV antibodies based on egg lay order, offspring gender, and plumage pattern. 

In songbirds, we use comparative studies to illuminate the principles of evolution of immunity and the immune system. We utilize the life history strategy of the Brown-headed Cowbird, the principal North American brood parasite, to compare life history parameters of cowbirds vs related non-parasitic species.  We predicted differences in disease resistance among the blackbird species based on differences in life history, because they differ in geographic range and life history traits of that include mating and breeding systems. In particular, based on our extensive earlier work on cowbirds, we predicted that the cowbirds would be significantly more disease-resistant than related non-parasitic species.  Higher exposure to parasites is the basis for parasite-mediated selection for increased diseased resistance.

Education/Training: 
Wellesley College, B.A.
Tufts University, M.S.
Rutgers University, Ph.D. 
Smithsonian Tropical Research Center, Post-doctoral Fellow
Harvard University, Museum of Comparative Zoology, Post-doctoral Fellow

Areas of Expertise/Interest:
Behavioral ecology
Ecological immunology
Life history
Evolution

Active Projects: 

Transmission and spread of infectious diseases: role of migratory songbirds

Immunological studies in the Screech Owl (Megascops asio): West Nile Virus Susceptibility

Evolution of immune systems: comparative studies of brood parasites and their relatives

Selected Publications/Products: 

Kozlowski, C. P., J. E. Bauman, and D. C. Hahn. 2009. A simplified method for extracting androgens from avian egg yolks. Zoo Biology 28(2):137-143. abstract

Reisen, W. K. and D. C. Hahn. 2007. Comparison of immune responses of brown-headed cowbird and related blackbirds to West Nile and other mosquito-borne encephalitis viruses. Journal of Wildlife Diseases 43(3):439-449. (PDF)

Hahn, D.C, N.M. Nemeth, E. Edwards, P.R. Bright, and N. Komar. 2006. Passive West Nile virus antibody transfer from maternal Eastern Screech-Owls (Megascops asio) to progeny, Avian Diseases 50(3):454-455. (PDF)

Nemeth, N.M., D.C. Hahn, D.H. Gould, and R.A. Bowen. 2006. Experimental West Nile virus infection in Eastern Screech Owls (Megascops asio), Avian Diseases 50(2):252–258. (PDF)

Hahn, D.C., J.S. Hatfield, M. Abdelnabi, J. Wu, L.D. Igl, and M.A. Ottinger. 2005.  Inter-species variation in yolk steroid levels and a cowbird-host comparison .  Journal of Avian Biology 36(1):1-7. (PDF)

Brittan-Powell, E., B. Lohr, D.C. Hahn, and R. Dooling. 2005. Auditory brainstem responses in the Eastern Screech Owl: an estimate of auditory thresholds. Journal of the Acoustical Society of America 118(1):314-321. abstract

Hahn, D.C, R.D. Price, and P.C. Osenton. 2000.  Use of lice to identify cowbird hosts.  Auk 117(4):943- 951. (PDF)