Salvaged skulls of the endangered Chacoan peccary collected in Paraguay are now in the collection at the Field Museum of Natural History.
I am interested in questions that address both basic and applied biology. My first independent research project as an undergraduate at the University of Wisconsin-Milwaukee looked at the effects of migratory waterfowl on the chemistry and biology of an urban lagoon. I found that the lagoon was heavily impacted by road salt but little impacted by nitrogenous waste from the waterfowl. At the same time I collected data on gull predation by peregrine falcons released into downtown Milwaukee. This led to a seasonal job in the Green Mountains of Vermont with the U.S. Forest Service studying the impact of hikers on the nesting behavior of peregrine falcons. This exposure to research early in my career was vital to my success in the profession of biology, and I urge all undergraduate students to conduct independent study as an integral part of their college experience.
My graduate work focused on the systematics and ecology of neotropical mammals. I've utilized molecular techniques to extract and amplify DNA from museum specimens of rare and extinct foxes to better understand their systematic relationships. In the early 1990's there were only a few labs working on “ancient DNA” and I was fortunate to work in the lab of Dr. Robert Wayne, a leader in the molecular systematics of canids, at UCLA. We were able to clarify the taxonomic position of Darwin’s fox as a distinct species endemic to Chile. While living in the Paraguayan chaco, my wife and I also worked on a captive breeding project of chacoan peccaries for the Zoological Society of San Diego. Some of the animals we cared for, as well as their offspring, are now living at the Phoenix Zoo, the San Diego Zoo, and most recently the Saint Louis Zoo.
My dissertation research focused on how small mammal communities are structured in agricultural, successional, and natural habitats in the central Paraguayan chaco. I investigated the population ecology of the vesper mouse (Calomys laucha) and its associated hantavirus Laguna Negra Virus. My results show that populations of vesper mice grow throughout the dry season and that this is associated with higher incidence of viral infection. Further, seroprevelance is higher in agricultural and successional habitats. This has clear implications for the transmission of the virus to humans. I have also observed that seroprevelence increases as the relative frequency of the rodent reservoir increases in the community.
The Ecology of Hantavirus in Western Paraguay
My students and I at UWSP work on a variety or research questions. Most recently we have been collaborating with the Wisconsin DNR conducting bat censuses around Wisconsin.
Recent publications
Yahnke CJ, 2006. Habitat use and natural history of small mammals in the Paraguayan chaco. Mastozoologia Neotropical, 13(1);103-116. PDF
Yahnke CJ, 2006. Testing optimal foraging theory using bird predation on goldenrod galls. American Biology Teacher, 68(8):471-475. PDF
Yahnke CJ, PL Meserve, TG Ksiazek, and JN Mills. 2001. Patterns of infection with Laguna Negra virus in wild populations of Calomys laucha in the central Paraguayan chaco. American Journal of Tropical Medicine and Hygiene, 65(6):768-776. PDF
Yahnke CJ, I Gamarra de Fox, and F Colman. 1998. Mammalian species richness in Paraguay: the effectiveness of national parks in preserving biodiversity. Biological Conservation 84:263-268.
Yahnke, CJ, WE Johnson, E Geffen, D Smith, F Hertel, MS Roy, CF Bonacic, TK Fuller, B Van Valkenburgh, and RK Wayne. 1996. Darwin’s fox: a distinct endangered species in a vanishing habitat. Conservation Biology 10:366-375. PDF
Yahnke CJ. 1995. Metachromism and the insight of Wilfred Osgood: evidence of common ancestry for Darwin’s fox and the Sechura fox. Revista Chilena de Historia Natural 68:459-467.