Longer ice-free seasons increase the risk of nest depredation by polar bears for colonial breeding birds in the Canadian Arctic

Abstract

Northern polar regions have warmed more than other parts of the globe potentially amplifying the effects of climate change on biological communities. Ice-free seasons are becoming longer in many areas, which has reduced the time available to polar bears (Ursus maritimus) to hunt for seals and hampered bears’ ability to meet their energetic demands. In this study, we examined polar bears’ use of an ancillary prey resource, eggs of colonial nesting birds, in relation to diminishing sea ice coverage in a low latitude region of the Canadian Arctic. Long-term monitoring reveals that bear incursions onto common eider (Somateria mollissima) and thick-billed murre (Uria lomvia) nesting colonies have increased greater than sevenfold since the 1980s and that there is an inverse correlation between ice season length and bear presence. In surveys encompassing more than 1000 km of coastline during years of record low ice coverage (2010–2012), we encountered bears or bear sign on 34% of eider colonies and estimated greater egg loss as a consequence of depredation by bears than by more customary nest predators, such as foxes and gulls. Our findings demonstrate how changes in abiotic conditions caused by climate change have altered predator–prey dynamics and are leading to cascading ecological impacts in Arctic ecosystems.

Anthropogenic flank attack on polar bears: interacting consequences of climate warming and pollutant exposure

“…In some regions, decline of sea ice extension has resulted in changes in the presence of seal species that polar bears depredate, and this has been shown to cause increased bioaccumulation of certain POPs (Thiemann et al, 2008;McKinney et al, 2009McKinney et al, , 2013. Dietary shift toward feeding on plants, berries and caribou (Rangifer tarandus) and seabird eggs, respectively (Ramsay and Hobson, 1991;Gormezano and Rockwell, 2013a,b;Iles et al, 2013;Iverson et al, 2014), will most likely decrease and increase, respectively, the dietary uptake of POPs. Furthermore, climate warming induced immigrating warm-adapted fish species (Valdimarsson et al, 2012;Mackenzie et al, 2014) may act as biovectors that increases contaminant levels in marine arctic ecosystems (Macdonald et al, 2005;Carrie et al, 2010), ultimately causing increased bioaccumulation of these compounds in polar bears.…”

Can polar bears use terrestrial foods to offset lost ice‐based hunting opportunities?

“…For instance, in western Hudson Bay, polar bears increasingly have been reported preying on birds and their eggs. Farther north, in Foxe Basin and Hudson Strait, documented increases in polar bear predation led to catastrophic effects on seabird reproduction (Iverson et al . 2014).…”

How Arctic Marine Birds Help Researchers Study a Changing North

“…As the extent of summer sea ice declines in some areas (e.g., the Hudson Bay/Strait region), the ice-free season becomes longer and so does the time that polar bears are forced to inhabit land. This decline in sea ice cover in the low Arctic has coincided with increased bear activity along coastlines and depredation of nests on marine bird colonies (Smith et al, 2010;Iverson et al, 2014). Such changes in ecosystem dynamics may have consequences for both the prey and the predator.…”

“…Declining levels of sea ice also affect the rate at which polar bears (Ursus maritimus) depredate nests of marine birds (Iverson et al, 2014). Polar bears typically use the sea ice as a hunting platform and move onto land only when the sea ice disappears with warming summer temperatures.…”

“…Collaborative community research efforts and education opportunities related to marine bird research continue to provide insight and capacity building with our northern partners (Mallory et al, 2006a;Provencher et al, 2013). Marine birds also offer long-term data sets that are helping us to understand how changing conditions may be affecting wildlife throughout the region (Provencher et al, 2012;Iverson et al, 2014). Through my own PhD research and as a member of the northern marine bird research team, I strive to carry on this collaborative approach to northern research, always keeping in mind that those who study birds in the North are more than just bird biologists.…”