Phenology Tracking by Migratory Mule Deer

At the largest spatial scale, migration is recognized as a strategy that allows migrants to exploit high-quality resources available on one seasonal range, while avoiding resource deficiencies on the other. However, much less is known about the fine scale movement behaviors that animals make during migration. This project aims to understand the importance of forage quality experienced during migration, and how the habitat quality of migratory routes influences survival and reproduction of migratory mule deer in the Wyoming Range. Spring migration is a critical time for migrants, in which they must recover from harsh winter conditions and prepare for upcoming reproductive costs. It is hypothesized that movement from low elevation winter ranges to high elevation summer ranges, allows migrants to extend the amount of time they are exposed to young, highly palatable forage. Following a wave of newly emergent, high-quality forage along elevational gradients, is known as surfing the green wave (or phenology tracking). We will evaluate if individuals that accurately surf the green wave benefit from enhanced nutritional condition and reproductive success. An additional objective of this study is to understand how changing climatic conditions, such as increased incidents of drought, may alter habitat quality along migratory routes.

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The video above shows mule deer surfing the green wave, as they move from low elevation winter ranges to high elevation summer ranges, during the spring 2013 migration. This video illustrates how plant growth changes across the landscape, and how deer move in response to these changes in plant growth and forage quality. Dark green pixels represent the highest quality forage, while light tan pixels represent the poorest quality forage. Each color represents a different deer, and each dot represents a GPS location from that individual. Large dots show movements from the current day, while smaller dots represent movements from previous days. At the end of the video, a legend displays, showing the surfing score for each deer’s migration. Deer with a score close to one efficiently tracked the green wave, while deer with lower scores were not able to track the green wave efficiently.

Gallery

Mule deer move from low elevation winter range to high elevation summer range. We monitor deer movements with GPS telemetry. This information helps us determine how deer move in response to changes in forage quality.

During migration deer spend a large amount of time foraging a stopover sites. Here is a map of the Wyoming Range mule deer's migratory routes and stopover sites. We monitor stopover sites during spring and summer to measure changes in forage quality.

Migratory routes of 70 migratory mule deer and the 15 stopover sites where field work for this project takes place.

The view from a typical, high elevation summer range. During summer, mule deer enjoy abundant forage at high elevations, but move to lower elevations during winter to avoid deep snow.

The view from a typical summer range, of a migratory Wyoming Range mule deer

What a typical low elevation winter range looks like for mule deer living in the Wyoming Range

Ellen records the percent cover and height of plants at a stopover site. This is component of our field research occurs on a weekly basis during spring and summer, in order to measure changes in forage species available to mule deer.

During spring and summer field work, we collect weekly plant clippings to measure changes in digestibility and nutrient content of key forage species.

Fecal samples are collected on a weekly basis during spring and summer, to measure changes in diet selection.

Each March and December, we recapture a total of 70 mule deer to assess pre- and post-winter nutritional condition. This information will be used to link the condition of the animal to its movement decisions during migration.

Contact

Ellen Aikens

PhD Student

Wyoming Cooperative Fish and Wildlife Research Unit
University of Wyoming, Dept 3166
1000 E. University Ave.
Laramie, WY 82071

Email: [email protected]

Gary Fralick

Wildlife Biologist

Wyoming Game and Fish Dept.

P.O. Box 1022

Thayne, WY 83127

Email: [email protected]

Project Lead

Ellen Aikens

Ellen is fascinated by animal movement strategies. For her PhD research, she studied the environmental drivers of migration using the Wyoming Range mule deer population as a case study.

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Funding & Partners

United States Geological Survey • National Science Foundation