Quantifying the demographic and population impact of avian cholera on northern common eiders in the face of ancillary threats and changing environmental circumstances

Emerging infectious diseases are on the rise globally; however, determining demographic impacts and the influence of disease on wildlife population dynamics remains a significant challenge. A poleward expansion of disease-causing pathogens has been predicted in association with globalization and climate change and historically unaffected Arctic wildlife may be particularly vulnerable to epidemic disease. My research examines the influence of newly emerged avian cholera outbreaks on northern common eiders (Somateria mollissima borealis) in the Canadian Arctic. Avian cholera is a highly virulent disease of birds caused by the bacterium Pasteurella multocida. I take advantage of a unique opportunity to investigate transmission dynamics and the impact of this disease on eider survival and reproductive rates in a marked population at Mitivik Island, Nunavut (64.030 N, 81.789 W). I also test hypotheses on ecological factors influencing spatial occurrence of the disease with data gathered from extensive site investigations, undertaken with the assistance of Inuit harvesters throughout the Hudson Strait region. To date, mass-mortality events have been confined to northern Québec (Nunavik) and Mitivik Island with annual mortality rates of up to 43% of the female nesting population at affected colonies. Consistent with expectations for a novel pathogen, case incidence increased in an exponential fashion during the initial wave of invasion (R0 = 2.5). Recurrent outbreaks were documented during eight consecutive breeding seasons at Mitivik Island and prolonged low-frequency transmission (Rt < 1) was evident at the epidemic tail—a hallmark of disease persistence facilitated by environmental transmission. Harvest mortality appears to be additive to disease mortality in this population, which is relevant because adjustment of hunting regulations is among the few logistically feasible interventions to conserve abundance. Demographic recovery has so far been constrained by a climate-mediated increase in the frequency of polar bear (Ursus maritimus) incursions onto eider breeding colonies and associated declines in nesting success. The causes and effects of emerging infectious diseases rarely operate in isolation from other ecological stressors and the types of information that I gathered informs scientific understanding of the interacting processes regulating population dynamics in the face of rapid anthropogenically-driven environmental change.