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Abstract: Yellowstone bison (Bison bison bison) are managed to reduce the risk of brucellosis (Brucella abortus) transmission to cattle while allowing some migration out of Yellowstone National Park to winter ranges in Montana. Intensive management near conservation area boundaries maintained separation between bison and cattle, with no transmission of brucellosis. However, brucellosis prevalence in the bison population was not reduced and the management plan underestimated bison abundance, distribution, and migration, which contributed to larger risk management culls (total >3000 bison) than anticipated. Culls differentially affected breeding herds and altered gender structure, created reduced female cohorts, and dampened productivity. The ecological future of plains bison could be significantly enhanced by resolving issues of disease and social tolerance for Yellowstone bison so that their unique wild state and adaptive capabilities can be used to synergize the restoration of the species. We recommend several adaptive management adjustments that could be implemented to enhance the conservation of plains bison and reduce brucellosis infection. These findings and recommendations are pertinent to wood bison (Bison bison athabascae), European bison (Bison bonasus), and other large ungulates worldwide that are managed using best practices within a risk framework. [Copyright &y& Elsevier]

Newly emerging plants provide the best forage for herbivores. To exploit this fleeting resource, migrating herbivores align their movements to surf the wave of spring green-up. With new technology to track migrating animals, the Green Wave Hypothesis has steadily gained empirical support across a diversity of migratory taxa. This hypothesis assumes the green wave is controlled by variation in climate, weather, and topography, and its progression dictates the timing, pace, and extent of migrations. However, aggregate grazers that are also capable of engineering grassland ecosystems make some of the world's most impressive migrations, and it is unclear how the green wave determines their movements. Here we show that Yellowstone's bison ( Bison bison ) do not choreograph their migratory movements to the wave of spring green-up. Instead, bison modify the green wave as they migrate and graze. While most bison surfed during early spring, they eventually slowed and let the green wave pass them by. However, small-scale experiments indicated that feedback from grazing sustained forage quality. Most importantly, a 6-fold decadal shift in bison density revealed that intense grazing caused grasslands to green up faster, more intensely, and for a longer duration. Our finding broadens our understanding of the ways in which animal movements underpin the foraging benefit of migration. The widely accepted Green Wave Hypothesis needs to be revised to include large aggregate grazers that not only move to find forage, but also engineer plant phenology through grazing, thereby shaping their own migratory movements., Competing Interests: The authors declare no competing interest., (Copyright © 2019 the Author(s). Published by PNAS.)

The wildlife of the Greater Yellowstone Ecosystem carries brucellosis, which was first introduced to the area by cattle in the 19th century. Brucellosis transmission between wildlife and livestock has been difficult to study due to challenges in culturing the causative agent, Brucella abortus . We examined B. abortus transmission between American bison ( Bison bison ), Rocky Mountain elk ( Cervus elaphus nelsoni), and cattle ( Bos taurus ) using variable number tandem repeat (VNTR) markers on DNA from 98 B. abortus isolates recovered from populations in Idaho, Montana, and Wyoming, US. Our analyses reveal interspecies transmission. Two outbreaks (2007, 2008) in Montana cattle had B. abortus genotypes similar to isolates from both bison and elk. Nevertheless, similarity in elk and cattle isolates from the 2008 outbreak suggest that elk are the likely source of brucellosis transmission to cattle in Montana and Wyoming. Brucella abortus isolates from sampling in Montana appear to be divided in two clusters: one found in local Montana elk, cattle, and bison; and another found mainly in elk and a bison from Wyoming, which is consistent with brucellosis having entered Montana via migration of infected elk from Wyoming. Our findings illustrate complex patterns of brucellosis transmission among elk, bison, and cattle as well as the utility of VNTRs to infer the wildlife species of origin for disease outbreaks in livestock.