Editor's choice: Where the buffalo roam – bison and brucellosis in Yellowstone

Abstract

Kilpatrick, A.M., Gillin, C.M. & Daszak, P. (2009) Wildlife–livestock conflict: the risk of pathogen transmission from bison to cattle outside Yellowstone National Park. Journal of Applied Ecology, 46, 476–485. An enduring symbol of the American West, great migratory herds of bison Bison bison once roamed the Great Plains in their millions (Berger & Cunningham 1994). Sadly, this wildlife spectacle is no more, as in parallel with population declines and extirpation in other migratory ungulates (Bolger et al. 2008; Harris et al. 2009), bison are now restricted to a number of small remnant populations. The causes of population decline in bison and other migrants are well known – hunting, habitat loss, fencing – and their need for space makes the conservation of these wide ranging species a major challenge (Berger 2004; Thirgood et al. 2004). The only free-ranging herd of bison remaining in the United States is found in the Greater Yellowstone Ecosystem of Montana, Wyoming and Idaho. At the start of the 20th century, this population had been reduced to 23 individuals, but with protection it has increased to nearly 5000. Bison spend most of the year at higher altitudes in the Yellowstone National Park but during severe winters they graze at lower elevations outside the park. Here they come into conflict with cattle ranching because of the risk of transmission of brucellosis from bison to cattle. Brucellosis is a bacterial disease that causes weight loss, abortion and reduced milk yields in cattle. The maintenance of brucellosis-free status in cattle is economically important to the livestock industry, and as a result, culling bison is part of the Government interagency disease control strategy (Clarke et al. 2005). The conservation success of Yellowstone's bison indirectly led to the culling of 1600 bison during the 2007/08 winter. For this issue's Editor's Choice selection, Kilpatrick et al. (2009) develop a quantitative risk assessment integrating both ecological and epidemiological data to assess the spatio-temporal risk of transmission of brucellosis from bison to cattle. The model demonstrates that the risk of transmission is highly variable in space, time and frequency and can be predicted by climatic conditions and the abundance of bison. Critically, the model suggests that the risk of brucellosis transmission is very low in most years and is periodically high only in certain localized areas around the park. The authors suggest alternative management strategies, such as financially compensating ranchers for grazing rights in localized areas, would be more cost-effective than the current policy of culling bison to control population size. Another management proposal is to the consider the section of the Greater Yellowstone Ecosystem which occurs in Montana as a separate zone from the rest of the state in terms of brucellosis infection status and provide yearly testing of cattle in that zone. This would cost a fraction of the $2.5 million that the current management strategies cost per year. Similarly, compensating ranchers for the financial value of all the cattle that graze in the affected areas around the park would cost about half the current yearly amount. The results of Kilpatrick et al.'s study have generated considerable interest from scientists, managers and the general public – particularly in the United States. In the month since the paper was published online it has been picked up in the mainstream media more than 100 times. Perhaps this is a reflection of the iconic status of the bison in American popular culture – but it does highlight the critical role of good ecological research in influencing natural resource management decisions. The primary role of the Editor's Choice initiative is to showcase papers that we believe best fulfil the journal's mission of publishing ecological studies with management relevance. Kilpatrick et al.'s study is a particularly good example of the connection between good science and real-world problem solving and we expect that the paper will be both widely cited and highly influential.