LTREB: TESTING FOR FACULTATIVE SWITCHING BETWEEN MIGRATORY STRATEGIES IN A PARTIALLY MIGRATORY, LONG-LIVED LARGE HERBIVORE POPULATION

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Animal migrations figure among the most spectacular natural phenomena, ranging from Monarch butterflies that migrate up to 3,000 miles to over-winter in warm climates to Arctic terns that travel each year between the Arctic and the Antarctic. Migratory species are declining worldwide due to human disturbance, habitat loss, and climate change. In the presence of these ongoing changes, the ecology of migration has become an important management issue. This research extends a 15-year study of elk to understand why, across migratory species, there are individuals that migrate and those that do not migrate within a single population. The project will help understand the causes of migratory decision-making among elk and the implications of altered migratory behavior for elk conservation and management. The researchers will engage graduate students in journalism, who will develop diverse media outlets to communicate results broadly, and in geography, who will develop web interfaces for the public to view elk migration virtually. The project will offer internships to Native American students through the Native American Natural Resource Program at the University of Montana. General fascination with migratory animals along with the broad appeal of elk to conservationists, hunters, and Native Americans alike promise effective citizen outreach and engagement. The researchers will use a partly-migratory population of elk as a model system to understand the context-dependent costs and benefits of partial migration. The project builds on long-term knowledge of the demography of more than 300 individually marked female elk of known age, individual reproductive rates, and juvenile survival rates, combined with spatial analyses of migratory behavior measured by Global Positioning System (GPS) collars. The researchers will monitor both intrinsic factors such as age and reproductive history and extrinsic factors such as forage and predation risk to test competing and interacting hypotheses to understand why a long-lived mammal switches between migratory strategies in the face of environmental change. They will next incorporate results on the causes of switching into a population model that explicitly tests for the effects of switching on population dynamics. A Bayesian state-space population model, Bayesian model selection, and cross-validation of competing models with and without different switching functions will test between two alternate hypotheses for the population dynamic effects of partial migration as well as the relative importance of bottom-up (forage) versus top-down (predation) forces on population growth rates.