This week we welcome Grant Gilchrist.
How changing biodiversity in the Canadian Arctic is affecting seabirds: from pathogens to predators, bacteria to bears
We often view the Arctic as a pristine wilderness largely free of environmental threats. Times are changing. I’ll provide a few examples of changing conditions currently affecting eider duck populations in Arctic Canada: harvest, emerging diseases, and changing predatory regimes. Infectious disease is a potentially important driver of wildlife population dynamics although the demographic effects of disease in free-ranging hosts have proven difficult to quantify. Avian cholera is a highly virulent disease of birds that has circulated among common eider populations in Europe and North America for several decades. The disease has recently appeared in the Canadian Arctic where high annual mortality, coupled with near total reproductive failure on affected colonies, has raised fears over local extirpation and severe population decline. In this study, our group used data from a marked population of northern common eiders (S. m. borealis) to estimate vital rates before and during a multi-year cholera outbreak. Nesting success remains below replacement level and there has been no evidence for population recovery. Climate change can also influence species directly by modifying their physical environment or indirectly by altering interactions among organisms. Changes affecting the ecology of top predators are a particular concern because variation in predator behaviour has the potential to restructure food webs and lead to cascading ecological impacts on prey populations. Polar bears (Ursus maritimus) are a top predator in the circumpolar Arctic and are adapted to use sea ice as a platform to hunt seals. Advancement in the timing of sea ice break-up in the spring has recently reduced the access of seals to bears, and has been associated with increased bear predation of eider eggs on islands in summer. The proportion of days on which bears are present on eider duck colonies before their median annual laying date has more than doubled during the past two decades. Nest success has also declined raising concern about the long-term viability of ground-nesting bird populations such as eiders that are unaccustomed to such intensive depredation by bears.