Emperor penguins living in Antarctica are under threat from global warming, based on a new study. More than two-thirds of all colonies of the iconic birds could see population reductions of two-thirds before the end of the century, according to the investigation.

The new study used data from an investigation of one colony of the birds, in which researchers collected data for 50 years. That group makes their home in Terre Adelie, located in East Antarctica.

"Dynamics differ among colonies, but by 2100 all populations are projected to be declining. At least two-thirds are projected to have declined by [more than] 50 percent from their current size. The global population is projected to have declined by at least 19 percent," researchers wrote in an article announcing their findings.

An international team of researchers from the United States, the Netherlands and France are urging governments to list emperor penguins as endangered before population further decline.

"The role of sea ice is complicated. Too much ice requires longer trips for penguin parents to travel to the ocean to hunt and bring back food for their chicks. But too little ice reduces the habitat for krill, a critical food source for emperor penguins," Stephanie Jenouvrier, a biologist with the Woods Hole Oceanographic Institution (WHOI), said.

Leopard seals and killer whales hunt emperor penguins, but those animals are facing their own challenges in the warming environment of Antarctica.

Leopard seals are large marine mammals, with females growing to be over 12 feet long and weighing up to 1,100 pounds. Full-grown males are about two feet shorter than females, and weigh just 60 percent as much. They generally make their home on the ice floes of Antarctica, although they occasionally visit other nearby areas.

"Population size from the most recent circumpolar estimates, conducted in the summer of 1999/2000, indicates a total population size of 300,000... Within the last 30 years there has been no observed population reduction for the leopard seal, either observed, estimated, inferred, or suspected," researchers from the Society of Marine Mammalogy stated on their website.

Orcas, or killer whales, are sometimes known as the wolves of the sea for their habit of hunting marine mammals, including other whales. No attack on a human by an orca has ever been recorded in the wild. These animals live in colder waters around the world, so measuring populations is difficult. If populations of emperor penguins decline, this could make it more difficult for orcas around Antarctica to find food.

Investigation of emperor penguin populations and how they are affected by global warming was published in the journal Nature Climate Change.