Budapest Zoo's 18-year-old polar bear, Vitush, plays with a ball in his pool in Budapest, Hungary, Feb. 5, 2009.
Triton strikes a pose for visitors to the Roger Williams Park Zoo in Providence, R.I., in July 1999.
Melanie Stetson Freeman/Staff/FILE
Polar bear cub Wilbaer plays in the outdoor enclosure at the Stuttgart zoo in southern Germany, in April 2008.
A mother protects her cubs in Wapusk National Park on the shore of Hudson Bay near Churchill, Manitoba, Canada, in November 2007.
Jonathan Hayward/The Canadian Press/AP/FILE
Tourists crowd behind a glass wall to see a polar bear at a newly opened ocean park in Chengdu, China, on Aug. 26.
Vitus, an 18-year-old male polar bear, shakes off water on a sweltering day at the Budapest zoo on July 16.
Three-month-old Flocke plays at the Tiergarten Nurenberg zoo in Nuremberg, Germany, in April 2008.
Huggies carries one of her two newborn cubs at the Ouwehands Zoo in Rhenen, Netherlands, in March 2009.
Antonia swims in the Zoom Erlebniswelt amusement park in Gelsenkirchen, Germany, on July 20.
Zookeeper Thomas Doerflein shares a moment with polar bear cub, Knut, during Knut's first public appearance at the Berlin Zoo in March 2007.
A polar bear has a bucket on his head, while a cub swims nearby in the cooling waters of Moscow Zoo on July 21 as a heat wave hit central Russia breaking temperature records.
Kap relaxes in the Neumuenster Zoo in northern Germany on Jan. 6.
Zookeeper Harald Hager bottle-feeds polar bear cub Flocke at the Tiergarten Nuernberg Zoo in Germany in January 2008.
Flocke plays in her enclosure with her keeper as she experiences the open air for the first time in March 2008.
A polar bear is pictured underwater at the zoo in Gelsenkirchen, Germany, in December 2009.
Twin 6-month-old polar bear cubs play in the city zoo in St. Petersburg, Russia, on March 25.
A polar bear sprawls out in the snow, by a holiday-themed gift filled with bear treats, in December 2009 at the San Francisco Zoo in California.
A collared polar bear walks with her cub on the ice in Alaska in this undated photo from the US Geological Survey.
Steven Amstrup/US Geological Survey/AP
Charly, a 1,150-pound polar bear with a jack-o'-lantern, is seen at SeaWorld San Diego's Wild Arctic attraction.
Mike Aguilera/SeaWorld San Diego/AP
Charly sleeps in SeaWorld San Diego in California on Aug. 27.
Bob Couey/SeaWorld San Diego/AP
A polar bear rests at the zoo in Prague, Czech Republic, on Sept. 9.
Petr David Josek/AP
Knut plays in the water on Sept. 4 in the Berlin zoo in Germany
A polar bear is seen underwater at the zoo in Gelsenkirchen, Germany, in December 2009.