Subject

• Discuss the history of the pronghorn population of Yellowstone National Park.
• Translate raw data of pronghorn population numbers into a mathematical graph either by computer or by hand, per the instructor’s preference, with 100% accuracy.
• Cross reference at least 4 periods of significant pronghorn population fluctuation with corresponding historical occurrences, with 90% accuracy.

Materials
Computer and printer access or graph paper, pencil
Six fruits (banana, orange, watermelon, grape, kiwi, and pear)
Attachment A—Summary of Estimated Pronghorn Numbers in Yellowstone National Park, 1890-2005 (pdf)
Attachment B—Pronghorn History in Yellowstone National Park (pdf)

Background
When Yellowstone became a national park in 1872, the pronghorn population was reported to be in the thousands. However, the number of these animals declined as the Yellowstone area became settled. In addition, hunting continued in the park until 1883. By 1886, when the U.S. Cavalry arrived to administer the park, the pronghorn had been largely decimated. The Cavalry took measures to increase the number of these animals. Their tactics, controlling predators and providing supplemental feed, proved successful almost immediately.

Beginning in the summer of 1904, 50 acres of alfalfa inside the park were planted, irrigated, and subsequently harvested to yield about 100 tons of feed per year. As anticipated, the population of pronghorn increased when the animals were fed alfalfa. But beginning in 1907, a series of harsh winters, abruptly ended the population growth.

In 1918, the newly created National Park Service replaced the U.S. Cavalry’s management of Yellowstone National Park. Pronghorn numbers increased gradually, probably due to continued predator control, feeding programs, and natural recovery of the species. Beginning in 1925, feeding was expanded as important winter ranges were acquired from private landowners. This same area, now known as the Gardiner Addition, was annexed to the park in 1932.

In 1934, supplemental feeding was discontinued, and the predator control program was terminated in 1935. Prolonged drought, during the early to mid 1930s, dramatically affected the range condition. These factors affected the number of pronghorn, but the population appeared to recover between 1938 and 1945. Although limited personnel made reliable counts difficult to obtain during World War II, it is likely that the population during this time remained relatively stable at its pre-drought level.

In the summer of 1946, Yellowstone management approved a plan to reduce the pronghorn population to 400. Wildlife managers recommended further reductions because studies indicted that the range could not support more than 125 pronghorn. To keep the population at the targeted 125, at least 1,144 pronghorn were removed from the park between 1947 and 1967.

Following the end of the reduction program, pronghorn counts remained between 102-196 animals for the next 15 years. In the 1980s, the population began to increase, culminating with a high of 588 animals in 1991. During this period, the only major decline occurred in the winter of 1988-1989, following a summer of severe fires.

Since 1991, the Yellowstone pronghorn population has declined by approximately 50 percent and now hovers between 204 and 235 animals. Research is underway to determine possible causes. This decline is a concern because current research indicates that such a small, isolated population is susceptible to extinction from fairly common-place natural events such as a severe winter or disease outbreak.

Discussion Points for Students
What factors have led to decreases in the Yellowstone pronghorn population? What factors have led to increases in the Yellowstone pronghorn population? Why did park managers believe reducing the number of pronghorn was desirable at one time? What events could lead to the extinction of the Yellowstone pronghorn?

Procedure
The instructor will:

1. Lead a discussion about the information provided in the background section.
   
2. Provide the students with Attachments A and B.
   
3. Direct students to create a line graph (either by computer or by hand) of pronghorn population numbers in Yellowstone National Park, using the information on Attachment A. Pronghorn numbers should be on the “Y” axis and dates on the “X” axis.
   
4. Direct students to refer to Attachment B and cross reference major population fluctuations with Yellowstone pronghorn management events by drawing an arrow to indicate the area of fluctuation and describing the event.

Assessment
The Rise and Fall of the Yellowstone Pronghorn Rubric (pdf)