Polar Bear Summer

Chinook enjoys a lettuce snack.

Chinook enjoys a lettuce snack.

Summer is finally here, and what does that mean for the San Diego Zoo’s polar bears? How do Chinook, Kalluk, and Tatqiq do in the warmer weather? First, you need to understand how polar bears in the wild do in the cold. Polar bears are specially evolved to survive in the Arctic cold primarily with their fat layer. Yes, they do have thick fur and hide, but it is the fat that provides the key to survival. Polar bears are efficient at digesting fat from the food they eat. The fat develops on their abdomen first, then over their rear ends, and then disperses over the entire body. They also get the majority of their fresh water from this metabolic process. There is little fresh water in the Arctic except if one eats snow or ice, and that burns up a lot of needed calories!

The fat layer provides great insulation against the Arctic winds. A polar bear must have a minimum of 4 inches (10 centimeters) of fat to survive the cold. It also provides buoyancy if the bear needs to swim. The layer of fat also provides energy storage when a meal is not around. This energy storage is especially critical for pregnant females that can go without eating for as long as eight months in some areas of the polar bear’s range. The wild diet of the polar bear is 90 to 95 percent fat to provide the fat layer.

In San Diego, Chinook, Kalluk, and Tatqiq have a diet that is only 5 to 10 percent fat. This gives them the right amount nutritionally for our climate but doesn’t give them the amount of fat to build a fat layer for warmth! But yes, they think they should get more. And that is where all the carrots come in to play. We give them as many carrots as they want all day, every day. They really do like them! The bears are never hungry since any time they want a snack they eat their carrots. And although no real study has been done on the ability of polar bears to absorb calories from carrots, from years of picking up the (ahem) piles after digestion, it would appear they go right through!

Another benefit of carrots: the crunching keeps their teeth beautifully clean. Zoo guests are always surprised to see all the carrots, thinking polar bears are carnivores. They ARE the most carnivorous of all the bear species, but in the wild they do eat kelp, grasses, leaves, and berries if they can find them. However, the nutrition they receive from any vegetation is not enough to live on for this specialized bear.

And you are now all asking, But what if Chinook is pregnant? Doesn’t she need more of a fat layer? YES. We have already begun to raise her weight up in the event she dens up and has cubs. She is currently almost 15 percent above her normal weight, and the plan is to continue to allow her to gradually gain weight. Remember: a newborn polar bear is only 1½ to 2 pounds (0.6 to 0.9 kilograms). We don’t want her to put on too much weight either, as she needs to remain comfortable in the den and not feel too warm. Hint: When looking at “who’s who” on Polar Cam, Chinook is the roundest!

There is another way our polar bears stay cool in the summer and even year round in San Diego: our 130,000-gallon (494,000-liter) pool is chilled. We typically keep it between 55 and 60 degrees Fahrenheit (13 and 15 degrees Celsius). We can chill it more, but our San Diego bears won’t go in then. Remember: They don’t have that extra insulation! You can expect to see them swimming more often in the summer and playing as well.

JoAnne Simerson is a senior keeper at the San Diego Zoo.

P.S. Still no word on Chinook. We are moving ahead as though she is pregnant, but we won’t know for sure until we see cubs sometime this fall.

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