by Dr. Louise Beyea, Lake Superior Zoo Veterinarian
Feeding zoo animals is full of challenges. In order to keep animals healthy, it’s important to
provide them food that is as close to what they would eat in the wild. From tiny hedgehogs that
eat primarily insects, to grizzly bears that can grow to 1,000-pound-plus giants, zookeepers are
called upon to be extraordinary chefs when designing menus for the animals under their care.
Lake Superior Zoo keeper Lizzy Larson found herself doing a lot of homework when the zoo
obtained two orphaned grizzly bear cubs last year. She gathered information from other
accredited zoos, wildlife research journals, the Association of Zoos and Aquariums Nutrition
Advisory Group and biologists who work with state fish and game departments to determine
how to feed growing bears.
Grizzly bears are omnivores - they eat plants and meat. In the wild, bears have been observed
grazing on new spring grass, feasting on spawning salmon, catching new moose calves, and
gobbling late summer berries. Their food intake varies widely based on the season of the year,
and what’s available in the local ecosystem.
Tundra and Banks, the orphaned grizzly bear brothers, came to Duluth from Valdez, AK, and are
know as costal bears. Costal grizzlies depend primarily on salmon for the meat portion of their
diet, while bears that live further inland get most of their meat from moose calves in the spring.
Lizzy said that she learned in her homework that the size of costal brown bears is highly
correlated to the amount of salmon in their diet. Researchers in Canada compared the size of
hunter-killed bears along the Canadian and Alaskan Pacific Coast, and found a steady increase
in the size of coastal bears from south to northwest. The change in bear size roughly correlated
with an increase in the proportion of salmon consumed by the bears. These researchers also
noted that plant quality affected body size in bears.
Since Tundra and Banks came to the Lake Superior Zoo at a young age, they’ve not had to
experience periods of extreme food shortage that bears in the wild can experience. This means
the brothers will likely grow to be very large bears. Just how big will they get? Ask Lizzy in about 2027. Skull measurements show male Grizzly bears continue to grow until they reach eight
years old, according to the Canadian research.
At a year and a half old, Tundra and Banks are consuming about 3,000 calories a day, Lizzy
said. She expects that when the boys are adults, they will be consuming about 10,000 calories a
day in the summer months.
The bears’ diets are varied from day to day for variety, and month to month based on their
growth rate. Seasonal variations are also made to the diet because grizzly bears adjust their
behavior and metabolism in response to the changing seasons. Just like wild bears, grizzlies
living in captive situations respond to changes in day length and temperature and put on fat in
the fall to prepare for hibernation. But unlike wild bears, captive bears don’t go through periods
of semi-starvation in hibernation and thus don’t lose up to one-third of their weight. That extra
winter weight tends to add up and obesity has been a common problem in bears that live in
zoos.
To help manage the seasonal changes in the bear’s dietary needs, Lizzy has relied on research
done at the San Diego Zoo. Animal care staff in San Diego found that by reducing calorie intake
in the winter in spring they were able to keep their bears from gaining an excessive amount of
weight. Calorie restriction was accomplished by eliminating bear chow from November through
May, and changing the types of meat and produce offered at different times of the year.
The diets for Tundra and Banks include blueberries and strawberries for the berry portion, whole
salmon, rabbit or chicken for the meat portion, and cow legs or deer legs for the bone portion.
They can also be fed a beef-based ground meat diet that includes supplements for carnivores.
Vegetables include sweet and white potatoes, summer and winter squash, carrots (fed six
pounds at a time!) and romaine lettuce. Fruits offered include oranges, apples, pears, grapes,
bananas, melons and mangos. Lizzy said the amount of food fed to the bears is calculated
based on calorie count, not based on the weight of the food and the vegetarian portion of the
bears’ diet is never more than 50% fruit.
Last year, the cubs were being fed four times a day and their diet included a milk replacer that is
made for dogs, and they each got a pound of meat a day. This year, they are getting seven to
eight pounds of meat a day, in addition to a 50/50 mix of fruit and vegetables and some bear
chow. The food is divided into a morning snack, mid-day main meal, and late day snack.
The bears are weighed monthly, and both currently weigh over 300 pounds. The bears’ monthly
weight gain has ranged from 10 to 25 pounds this year.
Grapes are the bears’ favorite food and Lizzy has found that the bears get so exited to eat
grapes that she can’t use them as a reward when doing the bears’ training. The bears become
laser-focused on eating the grapes, and don’t follow instructions. “They are very food
motivated,” she said. “They just get too crazy with grapes.”
The bears aren’t so crazy about their bear chow, a specially formulated diet that looks like big
pellets of dry dog food. They definitely don’t like winter squash, Lizzy said. She knows that if the
bears leave their squash for a day that they aren’t quite as hungry as she would like.