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

Samuel A Iverson,Mark R Forbes,Anthony J Gaston,Paul A Smith,H Grant Gilchrist

doi:10.1098/rspb.2013.3128

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.

Highlights

Climate change can influence species directly by modifying their physical environment or indirectly by altering interactions among organisms [1]
The progressively earlier break-up of annual sea ice in low latitude regions of the Arctic has reduced the amount of time available to bears to hunt for seals and amass the fat reserves they require to sustain themselves on shore during the ice-free season [11,12,13,14]
We investigate whether the frequency of bear incursions onto bird colonies is correlated with sea ice conditions and ask whether nest depredation has increased as a result

Summary

Introduction

Climate change can influence species directly by modifying their physical environment or indirectly by altering interactions among organisms [1]. The polar bear (Ursus maritimus) is an apex predator in the circumpolar Arctic that relies on sea ice as a platform to hunt seals and other marine mammals. The progressively earlier break-up of annual sea ice in low latitude regions of the Arctic has reduced the amount of time available to bears to hunt for seals and amass the fat reserves they require to sustain themselves on shore during the ice-free season [11,12,13,14]. Earlier sea ice clearance is a major conservation concern for polar bears because it has been associated with deteriorating body condition, reduced demographic performance and population decline [15,16,17].

C Frobisher Bay

Results

Discussion

Findings

41. Thomas CD et al 2004 Extinction risk from climate