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The effect of fire, predation and vegetation quality on mule deer habitat use and fawn survival
Mule Deer BuckBackground:
Western states biologists have documented 2 declines in mule deer numbers since the 1960s. The reasons for decline are varied and often difficult to pinpoint. Because mule deer are so important to sportsman and the general public, the Arizona Game and Fish Department began to research desert mule deer decline by constructing the Walnut Canyon Enclosure at the Three Bar Wildlife Area in 1970. This predator proof enclosure allowed us to closely examine the effects of predation on fawn survival. In the initial study, we determined that fawn survival was approximately 30% greater in the absence of predators. In 1988 the gates to the enclosure were opened to allow animals to move in and out of the area until 1997. In early May 1996, the Lone Fire burned approximately half of the enclosure, so we once again used the enclosure and examined mule deer habitat use in predator-free, burned and unburned environments. In 2000, we introduced coyotes for 6 months to see if their presence changed deer habitat use. Even during our current drought, the predator free deer population continued to increase, prompting us to continue investigating the effects of different mule deer densities, vegetation quantity and quality, predation, drought, and deer nutritional condition in and outside of the enclosure have on mule deer fawn survival.

The 602-acre Walnut Canyon Enclosure (slightly smaller than a square mile) on the Three Bar Wildlife Area in the Tonto National Forest south of Roosevelt Lake in central Arizona.

Mule deer releaseVegetation data are collected each spring, summer, autumn, and winter, and deer density counts are taken each fall in a deer drive. We measure vegetation inside and outside the enclosure to look for differences among seasons and years at different deer densities (high inside, low outside). The deer drive is conducted using 60-100 employees and volunteers who form a line across the entire enclosure and walk from one end to the other. Each animal that passes through the line along the way is counted once, providing accurate information on the number deer and peccaries in the enclosure each year. Two graduate students from the University of Arizona completed the fire ecology portion of the study in December 2002, and 2 new graduate students (ASU East and Texas Tech Universities) will continue to work with research branch biologists over the next three years to look at habitat quality and deer nutritional condition.

The use of a large enclosure is similar to having an outdoor laboratory, and allows to control the predator component of population regulation. The original study that found fawn survival was greater inside the enclosure was during a six year wet period. However, since we closed the gates in 1997, Gila County, as well as much of the rest of the state, is in the worst drought that has occurred in the last 700 to 1,000 years. We did not expect the mule deer fawns within the enclosure to survive at as high of rates as they did in the wet period, but they have. Leaving us with the question, are predators more important than habitat in controlling deer numbers? That is why we have switched our emphasis to the habitat quality and deer nutritional condition. Certainly, there must be an interaction between habitat quality, deer nutritional condition, predation and fawn survival. Hopefully our large outdoor laboratory will help illuminate what conditions desert mule deer fawns need for optimal survival.

This project was conducted under the direction of
Stan Cunningham, Arizona Game and Fish Department, 5000 W. Carefree Highway Phoenix, AZ 85086-5000 .
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