Clipbirds Authors: Al Janulaw and Judy Scotchmoor

Overview: The classic bird beak activity usually involves having students attempt to pick up various objects with a wide variety of “beaks,” including scissors, spoons, etc. This traditional approach demonstrates competition in an ecological sense, but does not clearly demonstrate variation within a population, which is central to evolution. In the Clipbirds activity the “beaks” are all the same, except for size. The proportion of big-, medium-, and small-beaked birds changes in response to the available types of food.

Lesson Concepts:

• Evolution results from selection acting upon genetic variation within a population.
• Adaptations often persist in a population because they are in some way advantageous.
• Inherited characteristics affect the likelihood of an organism’s survival and reproduction.
• Evolution acts on what exists.
• The proportion of individuals with advantageous characteristics may increase due to their increased likelihood of surviving and reproducing.
• Speciation requires reproductive isolation.

Grade Span: 6–12

Materials: 1 1/2 lb unpopped popcorn 1 1/4 lb lima beans 255 marbles 20 large bulldog binder clips No. 3—2 5/8 inches 20 medium-sized bulldog binder clips No. 2—2 1/4 inches 20 small-sized bulldog binder clips No. 1—1 1/4 inches 30 plastic cups 1 Food Values transparency (pdf) 1 Clipbird Populations transparency (pdf) 1 Clipland Scene transparency (pdf) 1 overhead transparency projector

Advance Preparation: Gather materials.

Put the “food” in six bags, as below and label the bags according to the chart.

Time: One class period

Grouping: Initially, two groups of six, extending to most of the class

Teacher Background:

Evolution is the result of natural selection acting upon variation within a population. Organisms with favored traits within a given set of environmental circumstances have a selective advantage over individuals with different traits. It is this mechanism that leads to speciation. It is important to understand that favored traits are only advantageous within a particular situation and may not aid survival in another circumstance. A cat’s long tail may aid in balancing on a tree branch but be disadvantageous in a house with frequently closing doors. In the case of the fictitious Clipbirds, different types of food favor different beak sizes. One beak size is superior to another only in context.

Explore these links for additional information on the topics covered in this lesson:

• Adaptation
• Natural Selection

Vocabulary: evolution, variation, population, adaptation, advantage, characteristic, speciation, reproductive isolation

Procedure:

1. Display the Clipland Scene transparency and tell the class a fanciful but engaging story about a population of imaginary birds (Clipbirds) that lives happily in a faraway fictional place, known as Clipland. Point out to the class that somehow the large population became divided into two smaller populations, east and west. Perhaps a mountain range rose up in a big hurry, or a flock of the Clipbirds got lost and ended up on the opposite side of a preexisting range of mountains. (This is fictional, so have some fun with it.)
2. Ask the students to notice how the birds are alike and how they are different from each other. Help them to notice that the beaks of the birds vary in size. Big, medium and small.
3. Explain that birds of various beak sizes usually do just fine, but it takes more food energy to maintain the larger beak size than the smaller sizes.
4. Display the Food Values in Megacalories transparency. Allow students time to apprehend that the various foods have different food values and that birds of different beaks sizes have different needs.
5. Select six students to be east birds and six to be west birds. Within each group, give two students large clips, two students medium clips and two students small clips. Each student/bird also gets a plastic cup to serve as its stomach. Tell them that in order to eat, they must use the clips in the correct clip mode (demonstrate) and they must put all food that is successfully eaten into their stomachs.
6. Spread out the food for the 2nd Season in two places that represent East and West Clipland.
7. Give them 15 seconds to eat all they can. Make sure they do not scrape or shovel the food into their stomachs, as this will badly skew the results.
8. After the feeding frenzy, put up the Food Values transparency. Ask students to calculate the value of the food they ate. If a student doesn’t eat enough to survive then he turns in his beak and sits down. If a student ate enough to survive then she continues as part of the population. Each student who ate enough to reproduce gets another bill the same size as her own and selects a student from the audience to be her offspring.
9. Have a crew of students clean up all uneaten food from the floor.
10. Put up the Clipbird Populations transparency. Record 2 birds in each of the boxes labeled 1st Season because that was the initial number. Ask the now-living east and west birds to raise their beaks if they are now in the game. Include all surviving birds and their offspring. Record the numbers in the 2nd season boxes. (Note: these are the birds resulting from the 2nd Season of feeding.)
11. Repeat directions 6–9 with the food for the 3rd season.
12. Repeat directions 6–9 with the food for the 4th season.
13. Have all students turn in their beaks and clean up the mess.
14. Put up the Clipbird Populations transparency and ask students to write what they feel the numbers tell them.
15. Ask students to describe what happened to the Clipbird populations and what they think caused the changes.
16. Keep the discussion going so that students can assemble their understanding that selection can happen within a population that can favor one type over another.