"Across a 10-day period of observation we documented between four and six individual polar bears successfully capture at least nine flightless lesser snow geese and engage in at least eight high-speed pursuits of geese," wrote researchers from the American Museum of Natural History and the Hudson Bay Project after they tracked the dietary habits of polar bears on the western Hudson Bay (surrounded by Quebec, Ontario, Manitoba, and Nunavut) during its increasingly longer ice-free period.
Previous theory dictated that pursuing snow geese was less than common practice for polar bear because it wasn't energy efficient -- as in, the chase wasn't worth the end result. Hunts spanning over 12 seconds were deemed categorized as such, according to models written in the 1970's and 80's, but still follwed today; yet, researchers in this study timed polar bears in chase mode for over 15 seconds.
Even though they net less energy and nutrients, more efficient food sources are grass, berries, and eggs during the months when the ice recedes and energy-rich seal pups aren't available. As the ice melts earlier in the year, however polar bears aren't able to rely as much on seals to carry them in the lean months. Likewise, grass, berries, and eggs aren't nutritious enough without the support of winter seals. Not only has that reality affected their health and reproductive success, but it's forced them to devote more time to terrestial hunting.
As a result, past models have been deemed insufficient because they fail to consider other incentives previously filled by seals, such as to "enhance digestion, satisfy vitamin/mineral requirements, allow sampling of available foods to assess quality for potential switching, and dilute toxins," according to the study. Those factors have become more important as seals have become less plentiful.
It isn't as if energy efficiency isn't still a dietary factor; it's just not the only one. Researchers surmised that the bears tended to improve their geese hunting as they got older (younger bears had the slowest times) and employed a variety of techniques to more quickly net their prey.
"All but one of the chases we observed occurred in shallow water, and in several cases, polar bears appeared to be intentionally chasing flightless geese into coastal lagoons. Since flightless geese move more slowly in water than on land, chasing them into water may reduce the chase duration for polar bears."
Using the lagoon was also an important cooling device for a species equipped to live in arctic temperatures - and another sign that the bears were attempting to maximize energy efficiency for a prey requiring more work than grass and berries, but also more reward.
