Southeast Volusia Audubon Society, P.O. Box 46, New Smyrna Beach, FL 32170;   president@SEVolusiaAudubon.org


March 2014 Guest Column


Knock-on Effects of Global Warming

A scientific paper by Samuel Iverson, a PhD candidate at Carlton University in Ottawa, Canada, describes a previously undocumented knock-on effect of global warming.


The number of days of ice cover in the Eastern Arctic area of Hudson Straits and Northern Hudson Bay has declined by sixty days – freezing thirty days later in the fall and melting thirty days earlier in the spring.  The effect of this on Polar Bears is well known.  The bears cannot get offshore to catch seals for an extra month in the fall, making them thinner, and hence weaker, when they do get out.  Secondly, the ice often melts from below them when they are far from land, making it necessary to swim longer distances to reach land and safety.  Not all of them make it!


What Mr. Iverson has documented is the bears’ ability to adapt.  Birds’ eggs are high in protein and it seems some of the bears have learned they can provide food and energy, during a season where they historically fast, as they unhurriedly make their way back to the nearest river mouth.  There the ocean freezes earlier as it is diluted with fresh water.  The egg diet helps tide them over until they are able to get back to seal country.


Birds in the area of Iverson’s study are mainly Common Eider, which are ground nesters, and Thick-billed Murre, which are cliff nesters.  They nest on islands along the north coast of Quebec and the south coast of Baffin Island.  Eider nests are easy prey as they are handily within reach and the bear just walks from nest to nest, downing the three to four eggs in each as he passes.  Iverson and his crew witnessed a bear arrive at an island, where they had recently counted three hundred nests.  In a period of forty-eight hours, the bear cleaned out all but twenty-four of the nests, a loss of a thousand potential hatchlings.  One island reportedly had eight thousand nesting pair at one time and are now down to three thousand.  There are apparently other contributing factors to the decline, but bears certainly helped.


The Murre nests are more of a challenge, but some bears have learned to ascend the back side of the cliffs which are generally gentle slopes.  They then climb down from the top, cleaning out the nests, ledge by ledge, as they descend.  Only nests on the narrowest ledges survive.


Neither species are acrobatic fliers so reportedly they just vacate their nests and let the bears gorge in peace.  Saving the iconic Polar Bear is important but it ought not to be at the expense of two of the planet’s bird species.  It also begs the question “How many more of these knock-on effects exist that have not yet been discovered.”