Brooks River Brown Bears: Inheritance and Variation of Traits

Introducing the Brown Bears

Students find out about the brown bears that fish for salmon along the Brooks River in Katmai National Park, Alaska, and are introduced to the Guiding Question. The class watches a video clip, views photographs, and observes the physical and behavioral differences between bears at different life stages. After learning definitions of traits, students work in pairs to categorize brown bears’ specific traits as being either inherited or acquired.


Why are there differences between the ways individual brown bears look and act?


Teacher Materials

Student Materials

Lesson Preparation


Introduce the Brooks River Brown Bear

  1. Capture student interest by asking what they know about bears, such as the different kinds (species), where they live, how they behave, what they eat, and so on.
  2. Let the class know they will be watching video of brown bears that have come to fish for migrating salmon along the Brooks River in Katmai National Park, Alaska.
  3. Display the Katmai National Park and Preserve Map.
    • Point to the inset that shows the State of Alaska, and explain the state’s location relative to the continental U.S.
    • Point to the inset that shows Brooks Camp Vicinity, and trace the short length of Brooks River.
  4. Explain to students:
    • During the summer, the bears are super hungry because they haven’t eaten during hibernation through the winter and spring. They must eat an entire year’s worth of food in six months or less!
    • Bears gather at Brooks River because it’s the first place salmon become available to bears in Katmai.
    • The waterfall on Brooks River makes a barrier the salmon have to jump over in order to continue swimming upriver to spawn. Brooks Falls is a kind of bottleneck where bears count on finding fish in the first half of the summer.
  5. Tell the class that many of the same bears return year after year, and wildlife biologists know how to recognize them. Ask:
    • Can you think of ways the biologists might do that?

Introduce the Guiding Question

  1. Write the Guiding Question on the board: Why are there differences between the ways individual brown bears look and act?
  2. Tell students that their goal is to observe bears’ physical characteristics and behaviors and try to tell individual bears apart. They will practice by watching some video highlights from past years.


Watch Brown Bears

  1. Give the class two questions to focus on as they observe the bears:
    • What differences in physical appearance do you notice between one bear and another?
    • What differences in behavior do you notice between one bear and another?
  2. Show the Brooks Falls Highlight 1 video clip.
  3. Have students turn and talk with a partner about their observations. Expect to hear students comment on the cubs’ small size and darker color as compared to their mother and the cubs copying their mother by standing on hind legs.

Observe Physical and Behavioral Traits

  1. Tell the class that wildlife biologists use a combination of physical and behavioral traits to identify individual bears. Traits are the thousands of characteristics that make someone an individual. For example, everyone in the class has the physical trait of eye color or hair color; part of what makes each person unique are the differences between their hair and eye color and someone else’s.
  2. Ask the class:
    • How could you tell which bear(s) in the video were adults and which bear(s) were younger?
    • Did you use their physical traits, their behavioral traits, or both?
  3. Show the four photographs of bears at different life stages (Spring Cubs, Older Cubs, Subadult, and Adults). Encourage students to describe the differences they see between them. As a result of discussion, work with students to recognize that:
    1. Cubs in their first summer (spring cubs) are very small compared to their mothers. They usually have dark fur, and can sometimes have a band of lighter fur around their neck.
    2. Cubs in their second and third summers are taller than spring cubs and usually have lighter fur than spring cubs do. They are still dependent on their mother and follow her where she goes.
    3. Subadult bears are generally small to medium-sized. They have lanky bodies, which can make them appear to have a big head and ears. A bear’s coat generally darkens as it grows from a cub into an adult bear.
    4. Adult male bears can grow twice (2 times) as large as adult females.
  4. Explain that for any living thing, some of its traits are inherited and some are acquired through its life stages.
    • Inherited traits are the characteristics passed from biological parents to their offspring.
      • Inherited physical traits include eye color, ear shape, the hump on the back.
      • Inherited behavioral traits include instincts (such as salmon migrating up Brooks River or bears’ eating food).
    • Acquired traits are the characteristics an individual develops during their life.
      • Acquired physical traits include things that happen to someone (such as getting a scar, gaining or losing weight).
      • Acquired behavioral traits include things someone learns (how the bears fish for food—diving in the water, catching salmon in the air).

Identify Inherited and Acquired Traits

  1. Give each student the Katmai Brown Bear Identification handout, which describes observable physical and behavioral traits.
  2. Have students work in pairs to read aloud and discuss each trait and mark the right-hand column with one of the following:
    • “I” if they think the trait was inherited
    • “A” if they think the trait was acquired
  3. Once a pair has completed the sheet, have them meet with another pair to compare and discuss their answers. Let them know that the class will review answers in the next lesson.


  1. Give the class a cloze activity to evaluate their understanding of the difference between acquired and inherited traits. Write on the board:
    • An inherited trait means it is ______. An example of an inherited trait is ______.
    • An acquired trait means it is______. An example of an acquired trait is ______.
  2. Have students write the sentences and fill them in.
  3. Read students’ written responses to help you decide how deep a review to give in the next lesson.


Bear Years

  1. Have students calculate their age in bear years.
    • Print a copy of the Katmai Junior Ranger Bear Years handout for each student and have them fill it in. Or, write this equation on the board: (student age) / 4 = Bear Years
  2. Have students decide what bear life stage they would be:
    • Cubs (younger than 2½ years old): They are still dependent on their mother.
    • Subadults (between 2½ and 6 years old): They stay with their mother, but are not fully dependent.
    • Adults (older than 6 years): They usually don’t reach full size until they are 10–12 years old, and usually live to be about 20 years old.

Stream the Live Cam

  1. If online streaming is available in your school (and the month is right), link to one of the live cams hosted by
  2. Allow it to play during the class's free time. Alternatively, give the link to students so they can watch from home.

Clues to a Bear’s Sex

  1. Determine which sex characteristics to share with your class.
  2. Identify the ways students might distinguish between male and female bears:
    • If it is an adult bear with cubs, it is a female.
    • If it has visible genitalia, it is a male.
    • If a stream of urine goes in back of its hind legs, it is a female.
    • If a stream of urine goes straight down between its hind legs, it is a male.