"Long before it's in the papers"
January 18, 2011

RETURN TO THE WORLD SCIENCE HOME PAGE

Goose eggs may help save warmth-battered polar bear

Nov. 4, 2010
Courtesy of the Amer­i­can Mu­se­um of Nat­u­ral His­to­ry
and World Science staff

As cold-adapted po­lar bears floun­der for sur­viv­al amid a warm­ing Arc­tic, sci­en­tists pre­dict a new re­source—snow goose eggs—may sus­tain some po­lar bears for the fore­see­a­ble fu­ture.

In a stu­dy, re­search­ers with the Amer­i­can Mu­se­um of Nat­u­ral His­to­ry in New York con­clud­ed that im­por­tant­ly, lo­cal goose popula­t­ions can with­stand even re­peat­ed nest-raiding by hun­gry po­lar bears.

Polar bears near Hud­son Bay. (Cred­it: R. F. Rock­well)
The re­search, pub­lished in an early on­line edi­tion of the re­search jour­nal Oikos, of­fers glim­mers of hope for a bear spe­cies whose prospects have had con­serva­t­ion­ists wring­ing their hands. The ice where po­lar bears live is grad­u­ally melt­ing due to glob­al warm­ing, forc­ing the an­i­mals in­to ever-longer, more dan­ger­ous swims to find food. Po­lar bears have been re­ported can­ni­bal­iz­ing each oth­er amid the dire cir­cum­stances.

A major po­lar bear popula­t­ion in the Hud­son Bay, Can­a­da, is among the most threat­ened be­cause its home range is rel­a­tively warm for po­lar bears to beg­in with. Eve­ry sum­mer, sea ice in the bay melts com­plete­ly, forc­ing the bears on­to shore.

But a new nu­tri­tional op­tion may be emerg­ing for the great white mam­mals be­cause, as sea ice breaks up ear­li­er in the spring, bears swim to shore ear­li­er al­so. There awaits a boun­ty of goose eggs that, in a past era, were noth­ing but bro­ken shells by the time bears showed up. Now, still un­hatched, they of­fer a nu­tri­ent-rich pack­age for early-worm bears.

One wor­ry, though has been that “po­lar bears can ex­tir­pate snow geese quickly once they start to eat eggs,” said Rob­ert Rock­well of the City Uni­vers­ity of New York, who is al­so a re­searcher at the mu­se­um.

But luckily for the bears, “there will al­ways be the oc­ca­sion­al mis­match in the over­lap be­tween the on­shore ar­ri­val of bears and the in­cuba­t­ion pe­ri­od of the geese. Even if the bears eat eve­ry egg dur­ing each year of com­plete ‘match,’ our mod­el shows that pe­ri­odic years of mis­match will pro­vide win­dows of suc­cess­ful goose re­pro­duc­tion that will par­tially off­set preda­t­ion ef­fects.”

Com­put­er mod­els used in the research in­di­cat­ed that the mis­match is some­thing both bears and geese can use to their ad­van­tage. The tim­ing of geese migra­t­ion is pri­marily based on the length of the day. This won’t change as quickly as bear move­ments, which are based on the melt­ing of sea ice. Re­sults in­di­cate the ad­vance in ave­rage over­lap of the two spe­cies gives an ad­van­tage to the be­lea­guered bears. But in­creased vari­abil­ity, al­so the re­sult of cli­mate change, leads to an in­creased mis­match that is good for snow geese, Rock­well ex­plained.

“Mis­match is of­ten thought to be bad, but in this case pe­ri­odic mis­match is good be­cause it keeps geese from go­ing ex­tinct and al­lows po­lar bears to eat,” said Rock­well. “Are po­lar bears adapt­a­ble? Of course. This could be a nice sta­ble sys­tem. The geese aren’t go­ing to go away.”

* * *

Send us a comment on this story, or send it to a friend

 

Sign up for
e-newsletter
    
 
subscribe
 cancel

On Home Page         

LATEST

  • B­irds may at­tract mates with “sca­ry mo­vie” ef­fect

  • W­hy do men use sil­ly pick­up lines?

EXCLUSIVES

  • From bra­in sci­ence, new ques­tions about fr­ee wi­ll

  • Scien­tists ex­plore whe­ther some ap­es shake he­ads for "no"

  • It se­ems we're all more hu­man than aver­age

  • Ba­by temper­ament found to pre­dict ad­ult bra­in struc­ture

MORE NEWS

  • What hit the Mo­on? New cra­ter makes a spl­ash

  • T­racks may tell tale of rep­tilian land con­quest

  • Plan­ets found shar­ing strange dan­ces

  • Newfound sta­rs seen sha­ttering known si­ze lim­its

As cold-adapted polar bears flounder for survival amid a warming Arctic, scientists predict a new resource—snow goose eggs—may sustain some polar bears for the foreseeable future. In a study, researchers with the American Museum of Natural History in New York concluded that importantly, goose populations can survive even repeated nest-raiding by hungry polar bears. The research, published in an early online edition of the research journal Oikos, offers glimmers of hope for a bear species whose prospects have had conservationists wringing their hands. The ice where polar bears live is gradually melting due to global warming, forcing the animals into ever-longer, more dangerous swims to find food. Polar bears have been reported cannibalizing each other amid the dire circumstances. A polar population in the Hudson Bay, Canada, is among the most threatened because its home range is relatively warm for polar bears to begin with. Every summer, sea ice in the bay melts completely, forcing the bears onto shore. But a new nutritional option may be emerging for the great white mammals because, as sea ice breaks up earlier in the spring, bears swim to shore earlier also. There awaits a bounty of goose eggs that, in a past era, were nothing but broken shells by the time bears showed up. Now, still unhatched, they offer a nutrient-rich package for early-worm bears. One worry, though has been that “polar bears can extirpate snow geese quickly once they start to eat eggs,” said Robert Rockwell of the City University of New York, who is also a researcher at the museum. But luckily for the bears, “there will always be the occasional mismatch in the overlap between the onshore arrival of bears and the incubation period of the geese. Even if the bears eat every egg during each year of complete ‘match,’ our model shows that periodic years of mismatch will provide windows of successful goose reproduction that will partially offset predation effects.” Computer models used in the new studies indicated that the mismatch is something that both the bears and geese can use to their advantage. The timing of geese migration is primarily based on the length of the day. This won’t change as quickly as bear movements, which are based on the melting of sea ice. Results indicate the advance in average overlap of the two species gives an advantage to the beleaguered bears. But increased variability, also the result of climate change, leads to an increased mismatch that is good news for snow geese, Rockwell explained. “Mismatch is often thought to be bad, but in this case periodic mismatch is good because it keeps geese from going extinct and allows polar bears to eat,” said Rockwell. “Are polar bears adaptable? Of course. This could be a nice stable system. The geese aren’t going to go away, and they are a nutrient resource for the bears.”