Bison of the Past, Present and Future

Kathleen H. Fitzgerald

Alford, John J. 1973. "The American Bison: An Ice Age Survivor." Proc. Ass. Am. Geog. 5:1-6.

Seventy-five percent of the megafauna disappeared from North American at the close of the last Ice Age. Bison are an exception. Evidence from radiocarbon dates show that bison numbers peaked between 6,000-9,000 years B.P., decreased drastically in the mid-Holocene, and increased again 3,000 years ago. From 9,000-12,000 B.P. the historic bison range was centered further west and they were not present on the tall grass prairies. Approximately 6,000 B.P. bison abandoned the west coast and expanded their range east into the mid-western grasslands. Between 3,000-6,000 B.P. bison were confined to the grasslands west of the Mississippi river. In the succeeding three thousand years, the bison range expanded to include its historical range. These fluctuations are due to environmental stresses that occurred during the mid-Holocene. The exact cause is unknown. Alford cites the combination of late-Holocene bison range expansion and population increase coinciding with the human population expansion as an argument against the notion that humans are responsible for the decrease in bison population. Change in climate linked to the Altithermal is a possible explanation, however challenges to the Altithermal weaken the "climate cause" argument.

This is a basic, broad overview of bison population and range patterns, and possible causes of these fluctuations. Alford provides a good introduction to the historical trends of bison populations, yet merely skims the surface of the issue.

Antevs, Ernst. 1962. "Late Quaternary climates in Arizona." American Antiquity. Vol. 28, No.2.

Martin and colleagues have concluded from plant pollen and radiocarbon dating that the time of the Altithermal was subpluvial due to heavy summer rainfall. Antevs cites evidence for the late Quaternary as a sub-humid time, with the Altithermal being an arid period. Martin and associates use findings from two beds to support their claims of a moist period. Because these two soil beds are their only source, Antevs argues their claims are unfounded. Arroyo erosion is used by Martin et al. as support for heavy rains during the Altithermal, whereas Antevs uses it as evidence for drought. Historical storm and weather patterns support Antev's claims. The pollen used by Martin and others, composites and chenopods-araranths, have little climatological worth. Narrow tree rings support the arid Altithermal theory.

Antevs is recognized as the one who formally proposed the regional, middle-Holocene drought for the Southern High Plains (Dillehay 1974). His 1962 paper reveals the lack of data supporting his theory, the main reasons for his proposal and the opposing viewpoints of those who suggest the Altithermal was a moist period of time, such as Martin and others. The paper mirrors a boxing match between Antevs and Martin et al..

Dillehay, Tom D. 1974 "Late Quaternary Bison Populations Changes on the Southern Plains." Plains Anthropologist. 19:180-196.

An analysis of faunal lists from 160 archaeological and paleontological sites in the Southern Plains reveals two Bison population absence periods from approximately 6000-5000 B.C. to 2500 B.C. and A.D. 500 to A.D. 1200-1300. Temporal and spatial contours are responsible for long-term fluctuations in bison population and range shifts. The absence periods correspond with the Altithermal period, which would support the idea of a desiccated period because of a decrease of food. However, the Altithermal dates are not necessarily representative of the entire Great Plains. Temporal and spacial evidence may account for the lack of bison bones found in the archaeological and paleontological sites. Small groups of bison may have survived in isolated ecological niches during the two absence periods.

This paper was useful in providing a detailed analysis of the temporal and spacial outline of the presence and absence of the genus Bison using 160 sites in the southern plains.

Dobson, Andrew and Meagher, Mary. 1966. "The population dynamics of brucellosis in the Yellowstone National Park." Ecology. 77 (4).

The presence of Brucella in bison in Yellowstone National Park has caused extensive slaughtering of bison and has drawn local and national legislative attention. Brucellosis is a disease of ungulates caused by bacteria in the genus Brucella. Seriological and culture tests have been conducted on bison and elk to determine the presence of Brucella abortus. Sero-prevalence and culture tests indicate 60-70% and 10% presence of Brucella abortus among bison, respectively. This suggests that the sero-prevalence tests give a significant overestimate of the true level of infection. Seriological and culture test data reveal conflicting data for trends in brucellosis presence in relation to age, herd size and sex. The authors' analysis suggest that one would need to almost eradicate all of the bison to eradicate Brucella or inoculate more than 50% of the population with a Brucella vaccine. They conclude that neither is an option. Ensuring the cattle in adjacent areas remain in brucellosis free areas is suggested as the best option.

This is an informative paper providing data on population and eradication numbers of bison and elk, the relationship between sero-prevalence of Brucella and herd size of bison, the relationship between age and sero-prevalence for male and female bison culled in winter 1988-1989, and the relationship between bison population density and culture prevalence and sero-prevelence. The paper outlines useful mathematical models that can be used to predict population numbers and rates of infections. This paper is an excellent example of how science can be manipulated to prove a point.

Geist, Valerius. 1996. Buffalo Nation: History and Legend of the North American Bison. Voyageur Press. Stillwater, MN. pp. 17-37.

The bison's earliest ancestors were tropical and subtropical species in the extreme south of Asia millions of years before the Ice Age. Bison priscus, the Eurasian steppe bison, Bison latifrons, the large bison, Bison antiquus, the small bison, and Bison bison, the modern form, adapted morphologically to varying climate, vegetation change, and predator and human presence. The dispersal form, maintenance form and efficiency selection theories of mammals are used to support the varying forms of the Bison species.

Geist provides an excellent overview of how the bison evolved before, during and after the Ice Age. In addition, his book covers the hunting and extermination of the bison in the 1800's, bison myths and legends and the movement to save the bison.

Holliday, Vance T. 1989. "Middle Holocene Drought on the Southern High Plains." Quaternary Research. 31, 74-82.

Holliday provides evidence that the Altithermal is a period of warm, dry climate in western US from 7500-5000 yr B.P. Martin and others have long been arguing against this idea. The strongest evidence used to characterize the mid-Holocene climate of the Southern High Plains, northwestern Texas and eastern New Mexico, is geomorphic. Stratigraphic data from various draws are reported where sandy eolian sediment dated 5000 yrs. old is found on top of fen and lake sediments. Stratigraphic data reveal that a significant portion of the dunes in the great plains were created between 7000-4000 yr B.P. Studies of invertebrate and vertebrate faunas suggest warming and drying in the region. Archaeological records reveal water wells dug during the Altithermal indicating a decline in water table. Lastly, isotopic data from bison bone yielding a lower 13C value suggest a decrease in certain grasses sensitive to summer drought. Geomorphological, paleontological, and archaeological data show that in the middle of the Holocene the Southern High Plains were subjected to warmer climate with reduced precipitation. The reduced vegetation most likely caused a decrease in bison population.

Holliday provides a base line summary of the arguments used to support the Altithermal as an arid period. However, his data is lacking to fully support his arguments, which he admits.

Keiter, Robert B. 1997. "Greater Yellowstone's Bison: Unraveling of an Early American Wildlife Conservation Achievement." Journal of Wildlife Management. 61(1):1-11.

The American bison were saved in the late 1800's when Yellowstone National Park officials initiated a campaign to protect the remaining bison. Bison are now at risk from Brucella abortus, a bacterium that can cause brucellosis. A recent final interim plan calls for the National Park Service (NPS) and Montana officials, in conjunction with the US Department of Agriculture's Animal, Plant and Health Inspection Service (APHIS), to either shoot or capture, test and slaughter most of the bison straying outside the Park. Senate bill 745 was recently introduced to implement this plan. Legislation and authority dealing with the bison crisis is complex. The state nor federal livestock disease law originally extended to wildlife, however in 1962 Congress extended the Secretary of Agriculture's authority over contagious diseases to include all members of the animal kingdom, including wild animals. Montana and Idaho recently vested state livestock and agriculture officials with authority over bison that pose a contagious disease risk. In Greater Yellowstone, wildlife management responsibilities are shared among the NPS, United States Fish and Wildlife Service (USFWS), United States Forest Service (USFS) and state wildlife departments. Federal and state officials have entered a Memorandum of Understanding establishing the Greater Yellowstone Interagency of Brucellosis Committee as a forum to address management differences and to formulate a coordinated policy. Given the uncertainties and minimal risks associated with brucellosis, a revised policy, rather than an uncompromising eradication, could solve the problem.

This is a fantastic article clearly describing the threat of brucellosis, how individual states have handled the issue, the legal complications in addressing the crisis and the greater ramifications of the bison case.

Martin, Paul S. 1958. "Pleistocene Ecology and Biogeography of North America." Zoogeography. American Association for the Advancement of Science. Washington, DC. pp. 375-421.

The foremost events in terrestrial ecology of North America during the Pleistocene appear to include the climatic sequence proper with its attendant displacement of biotic zones, the arrival of prehistoric man, and the extinction of late Pleistocene vertebrates. Extinction of large mammals was mainly a Postglacial event. Late Pleistocene extinction affected mostly large animals. Bison, along with moose, elk, and white-tailed deer, probably survived in temperate forests while the grasslands were stripped of large herbivores. Extinction in Mexico and Alaska preceded that in the Rocky Mountains. In Florida and South America, extinction postdated the Altithermal, thus eliminated climatic change as an extinction cause. A model designed to illustrate probability of extinction includes body size, habitat and total range of species and helps in deciphering extinction patterns.

Martin, known for his overkill hypothesis, provides a thorough description of the late Pleistocene environment and vegetation. He explores how the environmental changes link to the arrival of man and to the extinction of mammals.

McDonald, Jerry N. 1981. North American Bison: Their Classification and Evolution. University of California Press. Berkeley, CA. pp. 10-37.

Bison is among the most recently evolved genera of large mammals. The appearance, expansion and contraction of the bison range correspond with the environmentally dynamic Ice Age of the late Cenozoic. Exposure to different Cenozoic environments resulted in varying selection for certain adaptive characters, thus the development of different species of Bison. Bison migrated across the Bering land bridge, which existed during the Illinoian and Wisconsin glaciation. Vast grasslands opened up between the Wisconsin and Holocene periods. Bison evolved from four genus. The earliest dated Bison remains are from the late Pliocene found in Central Asia. Bison is the only genus of Bovini that became well established in North America. The end of the Pliocene and early Pleistocene witnessed the radiation of Bovini and appearance of four modern genera. During this time, competition among herbivores was increasing, foraging quality was decreasing and Bovini responded by increasing their body size. The bison that entered North America were B. Antiquus, the small horned form Bison, and B. latifrons, the larger bodied form of Bison. B. latifrons probably went extinct in the late Wisconsin.

This is an excellent summary of the relationship between glaciation, vegetation change and bison dispersal and radiation. The subsequent chapters cover the following: classification of bison, morphological variation and variability of bison, bison adaptation to different environments, bison hybridization and generic drift, and an extensive appendix of radiocarbon measurements and dates. The entire bok is a superb resource on bison.

Meagher, Mary. 1989. "Range expansion by bison of Yellowstone National Park." Journal of Mammalogy. 70(3): 670-675.

Since the establishment of Yellowstone National Park in 1872, Bison bison have lived as an isolated population within the park. Bison to the north of the Park were exterminated during the 1860's. During the past couple decades, the population expanded from the traditional northern core along the Lamar River to areas outside the Park boundaries. The winter of 1975-1976 was extremely severe, covering the historical bison winter range with a hard layer. Bison numbers increased three-fold in the northern range between 1976-1987 and herds migrated west of the traditional winter range between 1975-1976. Between 1984-1985, 88 bison were killed outside the Park. Winter conditions subsequent to 1975-1976 were not severe and did not appear to contribute to the continued movements and increase in numbers. The largest movements to date were from 1986-1987, a mild year. Movements of 1976-1987 were not significantly correlated with population increase on the northern range. Availability of adequate forage of increased numbers was not a factor. Use of a plowed road probably facilitated movement and an increase in numbers. The present movement pattern may represent an intermediate stage between a migratory and nomadic pattern of land use.

To understand the current eradication of bison in the Yellowstone region, this paper is useful in providing a background on the geography of the Yellowstone region and where the bison are migrating. It provides insight on why the bison are moving out of their historical ranges.