Wildlife researchers are beginning to understand that a diversity of migratory tactics may sustain mule deer herd productivity, particularly when strategies are exposed to intermittently poor environmental conditions (i.e., severe winters, summer drought). Annual shifts in relative benefits of migration strategies—often described as the fitness-balancing hypothesis—may be key to minimizing dramatic population fluctuations that are challenging for managers and biologists to predict and adapt to.

Researchers at the University of Wyoming, Including PhD candidate Anna Ortega, are studying a diversity of migratory strategies in a partially migratory herd of mule deer sharing a common winter range in the Red Desert of south-central Wyoming.

The Project

University of Wyoming graduate student, Anna Ortega, is studying a diversity of migratory strategies in a herd of mule deer sharing a common winter range in the Red Desert of south-central Wyoming. The Sublette Mule Deer Herd exhibits three migratory tactics, including long-distance migrants that travel 150 miles to Hoback Basin for the summer (the world’s longest mule deer migration), medium-distance migrants that migrate 70 miles to the southern Wind River Range for the summer, and short-distance migrants that either travel less than 30 miles north or remain year-round as residents in the Red Desert. The primary objective of this research is to evaluate the costs and benefits associated with the different migratory strategies at an individual and herd level. This system is analogous to a diversified stock portfolio: weather and habitat conditions vary annually, and a diversity of migratory strategies ensures productivity and stability at the herd level, even in lean years.


Over the past eight years, Ortega and her colleagues have outfitted mule deer with GPS collars and have been able to track animals remotely over terrain that is often difficult to access.  Historical methods to track large ungulates used radio collars with very high frequency (VHF) radio signals that were manually tracked by wildlife biologists. The advanced GPS collars allow biologists to collect more precise data over larger areas—ideal for a migratory study where animals can move hundreds of miles.  Some mule deer monitored in this study travel over 150 miles between their winter ranges and summer ranges, making it one of the longest big game migrations in the lower 48 states.

The Need

Any contribution will go towards the cost of additional collars, captures, and fieldwork so that researchers can extend this important and timely research.  The Wyoming Migration Initiative and the Wyoming Cooperative Fish and Wildlife Research Unit will continue to monitor the movements and demography of the Sublette Mule Deer Herd for years to come. Maintaining a long-term research project, however, is dependent upon continuous funding.


Research on this portion of the Sublette Mule Deer Herd was initiated in 2011 by Hall Sawyer.  Dr. Matt Kauffman continued the project in 2014 and brought Anna on as a PhD student in 2017.   Anna has completed 3 summer field seasons and 4 fall seasons and expects to graduate in the fall of 2022.  Research will continue with another PhD student after Anna graduates so that long term trends in this mule deer population can be evaluated.


Anna Ortega is a PhD candidate at the Wyoming Cooperative Fish and Wildlife Research Unit at the University of Wyoming and is studying under the guidance and advising of Dr. Matthew Kauffman. Ortega is the recipient of the National Science Foundation Graduate Research Fellowship.

Dr. Matthew Kauffman serves as the Leader of the Wyoming Cooperative Fish and Wildlife Research Unit and the lead scientist at the Wyoming Migration Initiative.

Collaborators on this research include Dr. Kevin Monteith, Dr. Jerod Merkle, Dr. Ellen Aikens, and Dr. Hall Sawyer. This research would not be possible without the help and expertise of biologists at the Bureau of Land Management (BLM) and the Wyoming Game and Fish Department (WGFD), including D. Brimeyer (WGFD), P. Burke (WGFD), D. Clause (WGFD), S. Harter (WGFD), J. Kraft (WGFD), P. Lionberger (BLM), D. Lutz (WGFD), J. Randall (WGFD), A. Roosa (WGFD), B. Scurlock (WGFD), M. Synder (BLM), M. Thonhoff (BLM), M. Valdez (BLM), and B. Wise (WGFD).

Anna Ortega Biography

Anna Ortega

Anna Ortega graduated Summa Cum Laude from Fort Lewis College with a BS in Environmental and Organismic Biology and a GIS Certificate. She has twelve consecutive years of research experience in the fields of botany, pollination biology, ornithology, and ungulate ecology. Ortega has worked as a wildlife field technician studying piping plovers and red knots along the Chincoteague Bay of Virginia, as well as emperor geese and loons on the Yukon-Kuskokwim Delta of Alaska. She also worked as a botany intern in Nevada. In October 2015, Ortega began working for the Wyoming Cooperative Fish and Wildlife Research Unit as a wildlife field technician and GIS analyst. In January 2017, Ortega transitioned into a graduate program with an NSF Graduate Research Fellowship.

Images courtesy of: Benjamin Kraushaar


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