Data from: Elk migration influences the risk of disease spillover in the Greater Yellowstone Ecosystem

Wildlife migrations provide important ecosystem services, but they are
declining. Within the Greater Yellowstone Ecosystem (GYE) some elk (Cervus
canadensis) herds are losing migratory tendencies, which may increase
spatiotemporal overlap between elk and livestock (domestic bison [Bison
bison] and cattle [Bos taurus]), potentially exacerbating pathogen
transmission risk. We combined disease, movement, demographic, and
environmental data from eight elk herds in the GYE to examine the
differential risk of brucellosis transmission (through aborted fetuses)
from migrant and resident elk to livestock. For both migrants and
residents, we found that transmission risk from elk to livestock occurred
almost exclusively on private ranchlands as opposed to state or federal
grazing allotments. Weather variability affected the estimated
distribution of spillover risk from migrant elk to livestock, with a 7-12%
increase in migrant abortions on private ranchlands during years with
heavier snowfall. In contrast, weather variability did not affect
spillover risk from resident elk. Migrant elk were responsible for the
majority (68%) of disease spillover risk to livestock because they
occurred in greater numbers than resident elk. On a per-capita basis,
however, our analyses suggested that resident elk disproportionately
contributed to spillover risk. In five of seven herds, we estimated that
the per-capita spillover risk was greater from residents than from
migrants. Averaged across herds, an individual resident elk was 23% more
likely than an individual migrant elk to abort on private ranchlands. Our
results demonstrate links between migration behavior, spillover risk, and
environmental variability, and highlight the utility of integrating models
of pathogen transmission and host movement to generate new insights about
the role of migration in disease spillover risk. Further, they add to the
accumulating body of evidence across taxa that suggests that migrants and
residents should be considered separately during investigations of
wildlife disease ecology. Finally, our findings have applied implications
for elk and brucellosis in the GYE, and suggest that managers should
prioritize actions that maintain spatial separation of elk and livestock
on private ranchlands during years when snowpack persists into the risk
period.