An infectious disease outbreak and increased mortality in wild alpine reindeer

Abstract

Climate changes may lead to tipping points where the epidemiologicalcharacteristics of infectious wildlife diseases suddenly change, leading tooutbreaks. However, empirically documented cases of the extent to whichemerging infectious diseases (EIDs) affect populations of large vertebrates arefew, partly because of the limited surveillance of remote wildlife populations.EIDs may potentially lead to higher mortality than mean mortality levels. Here,we quantified the likely impact of digital necrobacillosis on the survivaland population dynamics of wild alpine reindeer (Rangifer tarandus)inHardangervidda National Park (NP), Norway. The outbreak of digitalnecrobacillosis in 2019 contributed to a decrease in the summer survival rate ofjuveniles to 51% compared to an average of 88% in 2005–2018 and 77% in 2020.However, since the outbreak mainly reduced juvenile survival, the impact onshort-term population dynamics was moderate, lowering the population growthrate (λ) before harvest from an average value of 1.18 (2005–2018) to 1.08 (2019)before harvest. In 2019, anomalous climate conditions with a high daily meantemperature combined with the highest recorded daily precipitation in late sum-mer were observed. Further studies are required to document the pathologicaldevelopment of digital necrobacillosis across demographic groups and proximateand ultimate causes of mortality. demography, digital necrobacillosis, disease ecology, National Park, population dynamics,reindeer, surviva