Extended Fallout, Climate Change

"Substantial open-water areas are now routinely encountered in May and the near shore seasonal ice environment upon which polar bears depend has been drastically altered."
Study team, Environment Canada/Carleton University Arctic research

"The polar bears just lumber around, press the eggs with their nose and lap up the contents."
"What we're seeing now is close to twelve days in a season where we might see bears on a colony."
"We re-surveyed the colony after the bear left of its own accord and counted 24 active nests."  (left intact out of 335)

Samuel Iverson, wildlife biologist, Carleton University

Postmedia News file    Northern common eiders are even more vulnerable because the large seaducks lay three to four plump eggs in nests on the ground.

 

The study of polar bear predation on Arctic bird egg colonies was recently published in the Proceedings of the Royal Society B, with Mr. Iverson its lead author. The study points to hungry polar bears exercising their option to devour whatever they can when their normal diet has been disrupted due to climate change, impacting heavily on seabirds in the Canadian Arctic; far more so than conventional nest robbers like foxes and gulls.

Far larger creatures as predators, polar bears' appetite far outstrips that of a smaller mammal or a bid. And the issue is being pointed out as a symptom of "cascading ecological impacts" evolving around climate change. In the Hudson Strait area between northern Quebec and Baffin Island, polar bears present seven times more frequently in bird colonies than they did in the 1980s.

PAUL J. RICHARDS/AFP/Getty Images   Hungry polar bears are becoming a bigger threat to seabirds in the Canadian Arctic than traditional nest robbers like foxes and gulls, researchers say in a study.

 

Fifteen to twenty years ago bears might wander into a colony for a mere day or two. Now, the sites that Environment Canada has been monitoring for 24 years, see polar bears remaining at bird colony sites to devour nested eggs for up to twelve days in a season. And the researchers attribute the increased predation rate to the shrinking Arctic ice season; close to two months shorter than it was thirty years earlier.

Polar bears make use of sea ice as a platform from which to hunt for their more traditional meals -- seals -- their favoured diet. When hunger pangs strike they will eat anything else they can muster up when the ice melts, leaving them stranded on land, unable to reach their usual seal food. Thick-billed murres, seabirds nesting on cliffs become a target, for their eggs. Not much a sitting bird can do to protect its nest against a ravaging, hungry bear.

Postmedia News file    Thick-billed murres, seabirds that nest on cliffs, are one target. 

 

Northern common eiders are vulnerable, laying three to four plump eggs in ground nests. The researchers found that bears; typically a single bear or a female with cubs, feasting on 34% of eider colonies. When bears feast so too do gulls, which the parent birds would normally fend against. The gulls become extremely attentive when the bears begin crushing eggs, and they rush to take advantage of whatever is left over from the ruined nests.

The field crew found 335 active nests at one Cape Dorset on Baffin Island eider colony. Returning several days afterward they discovered a polar bear eating eggs, accompanied by over 50 gulls delectating over the remains. "[It] was among the most definitive cases of near total nest destruction on a colony", the team reported. For when the bear had reached satiety there were only 24 nests left intact.

Scientists associated with the study state their opinion that this clearly points to the cascading downstream effects of widely acknowledged climate change. Hudson Strait and Northern Hudson Bay Narrows, representing the areas where the study took place, have experienced a two-month reduction in annual ice cover over the past thirty years.

This ecological alteration in nature's long-term pattern sees polar bears on land up to two months longer than they have been in the past, resulting in "unanticipated" effects on breeding sea birds, according to the study. Murres and eiders live long lives and reproductive failures can be ameliorated in succeeding years. "But if the frequency gets past certain tipping points, then you'd expect them to decline."

Though additional study is required to reach definitive conclusions, "...we definitely think that it is a concern", commented Professor Iverson.

Farzana Wahidy / Postmedia News file       Colonies of thick-billed murres and black-legged kittiwakes cover the rocky shores of Hantsch Island off eastern Baffin Island.