As winter grips the Northern Hemisphere tightly, many of us are happy to retreat to the comfort of our warm homes. But for some animals, this season plays a vital role in the formation of something necessary for their survival, ice. There is one thing that we are becoming increasingly sure about: not all winters are created equal. In some years, ice and snow blanket the ground until mid-spring, and in others, light dustings of snow only last for a couple days. For animals that depend on ice for survival, varying winter conditions year to year may provide challenges to finding food, breeding, and making it from one day to the next.
PLOS ONE has recently published several studies that take a closer look at three different animals’ relationship with ice: penguins, polar bears, and ivory gulls.
Searching for Emperor Penguin Breeding Grounds
Emperor penguins rely on Antarctic sea ice for breeding and foraging, but a recent study published in PLOS ONE may have uncovered a new breeding behavior, where the penguins utilize a different type of ice.
Using satellite and aerial surveys to observe four emperor penguin breeding colonies, the authors of this study discovered something unusual. Two of the penguin colonies always appeared on the ice shelf rather than where we expected them to be—on sea ice—but the other two colonies were on both ice shelves and on sea ice in different breeding seasons. Researchers used synthetic aperture radar to assess how the largest of the four colonies may sometimes breed on the shelf and other times on the sea ice.
The authors found that in years where sea ice forms late in the season, the colony relocates onto the ice shelf. Three of the four breeding colonies were in the warmest northern conditions in Antarctica, where sea ice formation is less reliable. What may be a new breeding behavior at these warmer sites could provide clues for understanding how this near threatened penguin species may cope with future sea ice loss.
Polar Bears on the Move
On the other side of the globe, Arctic polar bears also rely heavily on ice for hunting and breeding, but sea ice has declined by over 9% in the Arctic over the past 20 years. The authors of a recent PLOS ONE study investigated how these changes may impact polar bear movement around the Arctic. The authors of this study analyzed genes from over 2,700 polar bears to evaluate whether polar bear genetic diversity and structure have changed in the past two decades. They then compared current polar bear genetic patterns with past patterns during ancient climate fluctuations.
Scientists identified four geographic polar bear populations: Eastern Polar Basin, Western Polar Basin, Canadian Archipelago, and Southern Canada (pictured above). They found evidence of gene flow within the past three generations, from Southern Canada and the Eastern Polar Basin toward the Canadian Archipelago, an area thought by scientists to be a possible future refuge for polar bears as climate-induced habitat decline continues.
They also found that the current population shift may differ from previous periods with respect to sea ice variation during the Holocene, where polar bears may have used both the Canadian Archipelago cluster and part of the Eastern Polar Basin cluster as an interglacial refuge. The scientists suggest more genetic samples are needed, but documenting population changes in the past and present may aid in conservation efforts as sea ice continues to decline.
Ivory Gulls on the Icy Edge
Living their entire lives in the Arctic, the near-threatened ivory gulls have scheduled their activities around ice. Foraging, migrating, and breeding are all dependent on ice, but little data exists on their year-round location and timing of these activities. In a recent PLOS ONE study, scientists interested in following the ivory gulls’ movement around their Arctic habitat attached satellite transmitters to 12 ivory gulls on Seymour Island, Canada in 2010, and tracked their migration over four breeding seasons.
Scientists have long thought the ivory gulls migrate along the Greenland coast, but the tracking data shows that individual birds varied the timing and their routes greatly. Ivory gulls avoid flying over open water, and scientists suggest birds may vary their migration route with the variations in sea ice formations. Further analysis of their movement revealed that the ivory gulls overwintered near the ice edge in Davis Strait and the Labrador Sea, which likely provided them with a consistent source of food, like fish, or scavenging opportunities, like polar bear remains.
Further research is needed to better understand these patterns, but may aid in predicting their ability to adapt to future sea ice changes.
While scientists are finding evidence that sea ice formation may be changing, they are also working to gain insight into animal behavior and develop conservation measures that might be designed around their current activities. While we humans in the Northern Hemisphere may be ready for winter to be over, animals at the Antarctic and Arctic poles may be hoping that more ice is on the way.
Citations: Fretwell PT, Trathan PN, Wienecke B, Kooyman GL (2014) Emperor Penguins Breeding on Iceshelves. PLoS ONE 9(1): e85285. doi:10.1371/journal.pone.0085285
Peacock E, Sonsthagen SA, Obbard ME, Boltunov A, Regehr EV, et al. (2015) Implications of the Circumpolar Genetic Structure of Polar Bears for Their Conservation in a Rapidly Warming Arctic. PLoS ONE 10(1): e112021. doi:10.1371/journal.pone.0112021
Spencer NC, Gilchrist HG, Mallory ML (2014) Annual Movement Patterns of Endangered Ivory Gulls: The Importance of Sea Ice. PLoS ONE 9(12): e115231. doi:10.1371/journal.pone.0115231
Image 1: Polar Bears by Ronald Kwok/NASA
Image 2: Figure 3 from 10.1371/journal.pone.0085285
Image 3: Figure 3 from doi:10.1371/journal.pone.0112021
Image 4: Figure 2 from doi:10.1371/journal.pone.0115231