CRACKING THE CURIOUS CASE OF THE GROLAR BEAR Overview Welcome to the Grolar Bear Challenge created by the Discovery Educator Network and Polar Bears ​ ​ International. Take part in this challenge before watching our webcast to better understand how bears size ​ ​ up to other creatures, compare grizzly and polar bears, learn about the rare grolar bear, and use your own creativity to help us problem solve. Then join us on Tuesday, November 10 at 1 p.m. (ET) for a live webcast from the tundra where PBI’s panel ​ of Arctic experts, plus the Discovery Educator Network’s Lance Rougeux, will discuss grizzly, polar, and grolar bears and how we use technology to understand the world around us. The questions in this challenge range from basic math to high-level creativity. Some questions have no right answer, but are designed to get students thinking outside of the box. Practicing problem solving gives students the tools and determination to figure out real-world problems they might encounter. You can view the answer key here. ​ ​ Discovery Education Resources From video segments to boards to interactive glossary terms, there are hundreds of resources in Discovery Education about polar and grizzly bears to help you in this challenge. A few of our favorites include: ​ ​ Also, search “polar bear” within Discovery Education and explore our brand new content collection. 1. Animal Birth Weights Every species must reproduce to keep surviving; it’s a fact of life! Because this is such a basic part of the life cycle, it may seem like it should be pretty simple and safe for the mother. However, giving birth can be dangerous for many animals, especially if the baby is large compared to the mother. Mothers who have very large babies compared to their own bodies are at greater risk for complications, whereas moms that have very small babies compared to their own bodies may face fewer risks during birth. We can use birth weight ratios between mothers and babies to tell us how big the baby is compared to its mother. A high ratio means the baby is large compared to its mother, while a low ratio means the baby is small compared to its mother. For example, we know that humans have large babies compared to the mother’s size, what we call a high birth weight ratio. Luckily, medical science has helped humans give birth more safely in the last century. To give an example, a 120 lb. woman can give birth to an 8 lb. baby. To find the baby:mother ratio, we take 8:120. Simplified that means 1:15 is the birth ​ ratio. The baby is 1/15th the size of mom, or the mom is 15 times bigger than the baby. Another example: The Kandula Asian elephant mom is 10,000 lbs. and her baby at birth is 324 lbs. That means the baby:mother ratio is 324:10,000 or 1:31. So the baby is ​ ​ 1/31 the size of mom. a. Just based on birth ratios, who might have the easier time giving birth? Elephants or humans? b. Bears have the smallest baby:mother ratio of any placental mammal. Baby bears are very tiny, pink, and helpless when they are born, helping to ensure the mother has an easy birth. They are nursed for months by their mothers before emerging into the world. Mei Xiang, the giant panda mom, weighed 238 lbs. when she gave birth to her two cubs. Her first cub was only 0.19 lb. So, 0.19:238 or 1:1256. This mom was 1256 times larger than her first cub. Mei Xiang’s second cub was 0.30 lb. How many times larger was Mei Xiang compared her second cub? c. For grizzly, or brown, bears, the mom has one to four cubs (usually two) every two years. Cubs are small and weigh only about 1 lb. at birth. If a mother grizzly bear weighs 300 lbs. when she gives birth to a 1 lb. cub, what is the baby:mother birth weight ratio? d. Polar bears are very similar to grizzly bears in their birth weight ratios, but slightly different in the number of cubs they produce. A polar bear female may start giving birth after 5 years of age and has between 1 and 3 cubs each cycle. If a polar bear female starts reproducing at 5 years old, gives birth to an average of 2 cubs every 3 years, and lives until she is 24, how many cubs will she have produced in her lifetime? 2. Adaptations Polar bears and grizzly bears are closely related; in fact, polar bears evolved from a grizzly bear ancestor. These bears have similar DNA and anatomy and can interbreed to produce hybrid offspring. Though they are genetically similar, each species has special adaptations that allow them to exploit different resources. Adaptations can change the way an animal or plant looks or the way it behaves, help it to survive the cold, the heat, to camouflage, and much more. Adaptations make different species unique and able to survive and thrive in their own habitat. For example, hibernation is a behavioral adaptation that grizzly bears have. In the winter, when the grizzly bear's food is covered by snow or unavailable, grizzlies enter their dens and hibernate throughout the winter. Hibernating lowers the grizzly bears’ body temperatures, heart rate, and need for energy. The need for food and water is eliminated and the bears are able to live off fat they stored on their body in the summer and fall. Male polar bears do not hibernate or slow their metabolism down at any point during their lives, even when there is little to no food available. Pregnant polar bear females enter dens in the fall, give birth in the winter, and emerge with their cubs in the spring to hunt seals. Though they are in dens and slowing down, even female polar bears don’t exhibit true hibernation but can go up to 8 months without eating. Grizzly bears have many other adaptations that help them find food and survive. For example, they have a distinguishing shoulder hump that is actually a mass of muscle, which enables brown bears strength to dig. Also, their claws are long, making them useful in digging for roots or digging out burrows of small mammals. Grizzly bears also have a range of teeth that have evolved to manage the variety of foods these bears eat. They have some sharp canine teeth but also flat molars that are well suited to eating and grinding vegetation. Polar bears’ heads are longer and narrower than grizzly bears’ allowing them easier access into seal holes. Their noses are very large to smell well, and their small, round ears are fur-covered, inside and out to prevent heat loss. Polar bear claws are shorter and more strongly curved than grizzly bears’, and larger and heavier than black bears’ claws, used for hooking seals in the water and dragging them onto sea ice. Polar bear teeth are sharp, and have evolved for grabbing prey and shearing meat. Unlike grizzly bear teeth, polar bear teeth are not well equipped for chewing vegetation. a. Thinking of adaptations, what advantage do grizzly bears have in being brown, and polar bears have in being white? b. Polar bears live in much colder conditions than grizzly bears. Can you think of at least two other adaptations that help polar bears survive in their icy home? c. From what you know so far, if you put a grizzly into polar bear habitat, how well do you think the grizzly would do at hunting seals? What advantages or disadvantages might a grizzly have in this icy habitat? 3. Diet The size of a grizzly or polar bear depends on gender, age, region, season, and diet. ​ ​ Grizzly bears are omnivores, which means they will eat almost any kind of food. Their diet includes mostly plants such as wild berries, grasses, flowers, tubers, wild vegetables, etc. They also eat bugs, rodents, and can attack larger animals, like elk or deer, for food. Grizzlies that live near coastal regions tend to be much larger as they have access to more calorie-rich food like salmon. They are one of the most adaptable bear species in the world because they can adjust to almost any kind of diet, therefore we can consider them generalists. Adult male grizzlies weigh on average ​ ​ 400–790 lbs., while most adult females weigh 290–400 lbs. The largest grizzly bear on record was found in Alaska and weighed in at about 1500 lbs. Polar bears are the most carnivorous of all bears and considered specialists due to their specific dietary and ​ habitat needs. Polar bears have evolved to use sea ice to find and feed on ice seals, specifically seal fat which is the highest calorie food source possible. Polar bears prey on both ringed and bearded seals across ​ their range, but will take other prey like beluga whales when available. When an adult bear is in good shape, polar bears will eat only the seal’s blubber, not its meat, in order to build up the fat reserves they need to sustain themselves between meals. In many populations, polar bears come onto land when the ice melts during the summer. On land they live off their own body fat because there are no seals, but will still eat whatever they can find. Unfortunately, terrestrial foods that polar bears eat (like snow goose eggs, berries, kelp, carrion) are less predictable and don’t provide enough calories or fat to sustain the polar bear's massive body size, let alone to add to its body fat.