8. Bird Beak Buffet

Inspired by observations of finches on the Galapagos Islands, Charles Darwin came up with an idea that is perhaps the most influential idea in all of science - natural selection. In this classic activity, students learn about natural selection by becoming birds foraging for food on an island (a large area of the schoolyard or classroom). The prey (beans) vary in their coloration such that some blend into the environment better than others. The birds vary in the type of beak they have (plastic forks, spoons and knives). Each season, any prey that survives has a baby bean the same color as the parent. In addition, the most successful birds has a baby with the same beak trait while the least successful birds die (and are reincarnated as the babies of the successful birds). Over several generations, the bird and bean populations shift depending on the environment. Well camouflaged beans survive and reproduce. Birds with beaks that can easily capture beans survive and reproduce. In this way, students model natural selection in 2 species and get a very good idea of how natural selection works.

Can explain what natural selection is and the conditions necessary for it to occur.
Can discuss changes in a population in the context of natural selection.
Can use terms such as natural selection, evolution, and adaptation scientifically.
Can organize data in a table and graph.
Can graph changes in a population over time.

Natural selection
Charles Darwin

Attachment Size
8bird_beak.doc 69 KB
bird_beak_student.doc 60 KB
bird_beak_data.doc 67.5 KB

8. Bird Beak Buffet - Logistics

15-20 minutes introduction
45-50 minutes activity (The lesson plan is written so that the activity is introduced on one day and actually done the following day. It is also possible to introduce the activity and go through one or two years on the first day and complete the activity on the following day.)
15-20 minutes organize and summarize data
30+ minutes discussion

Each student is a bird foraging in the same feeding ground. At the end of each year, students gather in a group of similar-beaked birds to enter their foraging results on a clipboard. The introduction and final discussion occurs as a whole class in a classroom.

** If working as a whole class in a single feeding ground is too chaotic for your students, then this activity may be done in smaller groups of 3 or 6. Each group will get their own 1 meter square plot of ground or even a cafeteria tray on a table in the classroom to forage in. Each group starts with 1 or 2 representatives of each of the 3 beak types in the group and 100 beans of each color in the feeding ground. After each season, they should summarize their data and add new beans to their feeding ground. The bird that eats the most will reproduce and the bird that eats the least will die and get reincarnated.**


  • 1 pound of red beans
  • 1 pound of black beans (of a similar size and shape as the other beans)
  • 1 pound of white beans (of a similar size and shape as the other beans)
  • 25 plastic forks
  • 25 plastic spoons
  • 25 plastic knives
  • 30 paper cups
  • 1 stopwatch
  • 1 whistle
  • broom and dustpan for cleanup
  • 1 copy of the Bird Beak student handout for each student
  • 3 copies of the Bird Beak data tables
  • 4 clipboards with a pencil/pen tied to each
  • Optional: masking tape or string to designate the borders of the feeding ground

The activity takes place in an 80 square foot (9x9 foot square) feeding ground located in the classroom, on a concrete school yard or in a grassy field. The introduction and post-activity discussion takes place in the classroom.

8. Bird Beak Buffet - Background

Teacher Background
Perhaps the most important idea in all of biology, or perhaps all of science, is the idea of evolution through natural selection. This idea by Charles Darwin provides the foundation of all of current scientific thinking in life science.

What is evolution? Quite simply, evolution is descent with modification. This includes both the idea that the frequency of a gene will change in a population over time as environmental conditions change and also the idea that new species descend from common ancestors over many generations. Ultimately, evolution can explain the vast diversity of life on this planet and the idea that all life on Earth shares a common ancestor.

Although there are many mechanisms for organisms to change over time, the most important of these is natural selection. It works in this way:

  • There is variation in a population. Different individuals have different traits.
  • There is heredity. Traits can be passed on from parent to offspring through our genes.
  • There is competition (sometime referred to as differential survival and reproduction) so that some individuals survive and reproduce more than others.
  • The end result is natural selection – the individuals with the traits that best fit the environment are most likely to survive, reproduce, and pass on their traits to the next generation. In this way, future generations, when viewed at the level of an entire population, will have more advantageous traits and fewer disadvantageous traits compared to their parents.

There are many other mechanisms for evolutionary change besides natural selection:

  • Artificial selection is a common practice for humans to breed together plants or animals with the most advantageous traits (the sweetest tomato, the most loyal dog, the fastest horse, etc.). Thus, future generations will have more of these traits.
  • Mutation can affect the distribution of traits by introducing a new trait to a population.
  • Migration can rapidly change the overall distribution of traits in a population when a group of organisms with different traits enters a new area. For example, a group of small beaked finches is blown over to an island with primarily large beaked finches by a hurricane.
  • Genetic drift can affect a population through a random chance event – like a hurricane or human activity – randomly destroying organisms with one trait but not another. For instance, when a new house is constructed in a neighborhood with both red and brown ground squirrels, it accidentally bulldozes the nest of the largest red ground squirrel family. Suddenly, brown ground squirrels predominate.

A final important term that is often misused by students is adaptation.  An adaptation is a trait that is very well suited to a given environment that has, through natural selection, increased in the population over many generations. Students often talk and think about adaptation as if an organism can try to adapt or is able to get what it needs. In neither case are they correct. An organism can’t get the genes it needs to survive by “trying”; it either has the genes or not. Similarly, natural selection doesn’t have a goal in mind and cannot give a creature what it “needs”; either the genes are there in the population or not.

In this activity, students come to understand natural selection, evolution and adaptation through modeling changes in 2 populations – a population of birds with different beak traits and a population of beans with different color traits.

Student Prerequisites
None required although an understanding of variation in traits is helpful (see Human Traits activity or Snail Variations project).

8. Bird Beak Buffet - Getting Ready

Getting Ready

  1. Purchase beans, cups and plastic utensils.
  2. Make copies of the Bird Beak student handout for each student.
  3. Make copies of the Bird Beak data tables. For each class that will do the activity you should have 3 copies of “_____-Billed Bird Population Data” and 1 copies of “Bean Population Data”. Attach these data tables to the 4 clipboards.
  4. On the 3 “_____-Billed Bird Population Data” clipboards, fill in the blanks with “Fork”, “Spoon”, and “Blade”.
  5. For each class or students, count out 100 red, 100 black, and 100 white beans and mix them together in a ziplock bag or cup.
  6. Optional: mark the feeding ground boundaries with tape or string.

8. Bird Beak Buffet - Lesson Plan

Lesson Plan
Day 1 - Introduction

  1. Open class with a discussion of what human traits might help a person be more successful (Is it an advantage to be tall? Is it an advantage in America to be blond haired and blue eyed? How about in another country like Africa or Asia?) Leave the interpretation of “more successful” open and somewhat vague. If this seems to controversial for your group of students, then discuss variation in cat or dog traits and what might help a pet survive better (Is it an advantage for a cat to be shy? Is it an advantage for a dog to be friendly?).
  2. Lead the discussion towards thinking about what “more successful” really means. Does that mean being more popular or making more money or more likely to live happily ever after? In scientific terms, what matters in the long run is whether you survive, find a mate, and reproduce, passing on your genes to the next generation.
  3. Introduce the activity. Pass out the handout and describe the rules.
  4. Check that students understand that all the birds are of the same species but have different beak traits. Similarly, all the beans are of the same species but have different color traits.
  5. Check that students understand that the birds that eat the most food will have a baby with a similar beak and that the birds that eat the least will die. Similarly, surviving beans (those not eaten) will have one baby with the same color trait.
  6. Finally discuss the data collection that occurs after each round. Each student is responsible for counting the number of each type of bean they eat and entering their data on the bird population data clipboards. Once all the bird population data has been gathered, then a volunteer from each group will report their data on the bean population data clipboard. 
  7. If data will also be collected in lab notebooks, have students copy or paste the data tables and graphs into their notebooks.

Day 2 – Bird Beak Buffet

  1. Distribute a cup to each student. Next, give each student a plastic utensil.
  2. Quickly go over the rules before heading out to the feeding ground. Make sure you bring clipboards, beans, a stopwatch, and a whistle.
  3. Place the 4 data clipboards in different locations near the feeding ground.
  4. Have students stand on the edge of the feeding ground. Sprinkle the mixed beans (100 of each type) into the feeding ground.
  5. Blow the whistle and give students 20 seconds to “eat” as many beans as possible. Look out for students that cheat (have cups touching the ground, interfere with other students, etc.) and dump out the contents of their cups or eliminate them from the game. Blow the whistle again to signal the end of the year.
  6. Each student should go to the clipboard for their beak type, count the number of beans of each type they ate, and enter that information in the data table.
  7. Each group should calculate the grand total number of beans of each type that were eaten by their group (the bottom row of the table).
  8. One volunteer from that group can bring that information to the bean population data clipboard and enter their groups’ information. The volunteers can then help to complete the bean data table and count out the proper number of beans to add to the feeding ground.
  9. While the volunteers are entering bean population data, the rest of the students should help to sort their beans by color and return them to the stockpiles.
  10. Finally, have students line up by the total number of beans they ate. Have the 5 students that ate the fewest beans act out a grisly death. (Acting out the deaths helps students realize that they are actually dying and entering the game as a new bird with new traits, not just trading in one tool for another.) Confiscate their utensils. Give them new beaks that match the beaks of the 5 students that ate the most beans.
  11. Have a student enter this information (the number of birds that died and number of babies born) on the bird population data clipboards.
  12. Repeat steps 5-11 for each of the next 3 years of the game for a total of 4 rounds.
  13. Collect the clipboards, cups and utensils. Sweep up any remaining beans.

Day 3 – Organize, graph and discuss data

  1. Create data tables on the board (or make and overhead copy) similar to the ones on the second page of the Bird Beak Student handouts.
  2. Use the information from the clipboards to fill in the summary table. Have students fill in their tables as well.
  3. Have students graph the data for each population (red beans, white beans, black beans, fork-bills, spoon-bills, blade-bills) with years 1-5 on the x axis and the number of organisms at the start of a year on the y axis. The graphing may be done:
    • individually in their lab notebooks
    • groups of 3 can each graph one bird and one bean and analyze graphs as a group
    • a group of students can create large poster sized graph for one of the populations to display around the room.
  4. Discuss the graphs. Notice patterns such as one population going up while another goes down. See if the population is growing steadily or exponentially.
  5. Discuss the reasons why one population did well while another did poorly. Is there a different scenario in which a different bird or bean would do best?
  6. At this point it is possible to formally address some of the vocabulary.
    • Discuss natural selection – the process by which organisms with traits that best suit the environment are most likely to survive, reproduce, and pass on their genes to the next generation. In this activity, the bean that had the best camouflage and that was the hardest to catch survived, reproduced, and passed on their genes.
    • Discuss evolution – descent with modification, most often as the result of natural selection. In this activity, we started with the same number of beans of each type but ended up with the population skewed towards the beans with the best suited traits.
    • Discuss adaptation – a trait that is very well suited to a given environment that has, through natural selection, increased in the population over many generations. In this case, a particular color of bean could be considered an adaptation since it increased in the population through natural selection.
  7. Describe Charles Darwin’s adventures on the Beagle and how his observations (particularly of the finches on the Galapagos Islands) led him to propose the idea of natural selection.
  8. Begin the process of busting the misconceptions that students have about evolution. See the Understanding Evolution website for a fabulous overview of the common misconceptions students have and responses to those misconceptions.
  9. Finally, return to the discussion you used to open this activity – what human traits might help someone be more successful – and revisit those issues in the light of what your students now know about natural selection and evolution. In particular, you can discuss whether and how natural selection has worked and is still working on the human species.

8. Bird Beak Buffet - Assessment


  1. Collect the students’ graphs and responses to the conclusion questions.
  2. Before the activity, have students write a short essay about “what is evolution and how does it work?” These may be collected to give you as the teacher a sense of what their initial understanding may be. After the activity and discussion, have students revise their essay to reflect what they now know about evolution.

Going Further

  1. Conduct a deeper investigation of the Galapagos finches. There are many resources that you can use to help you in this quest. First of all, read the Pulitzer Prize winning book The Beak of the Finch, by Jonathan Weiner. The book flips back and forth between Darwin’s original studies and the modern day work of Peter and Rosemary Grant. The Grants have spent over 20 consecutive years studying the Galapagos finches. They recognize each and every finch living on the island and know the family relationships between every individual bird. Several lesson plans for teachers have been developed from their work:
    • The PBS evolution site provides a downloadable pdf file with several graphs showing changes in finch beaks over time. One of PBS's online courses addresses some of the questions raised by the data and may be appropriate to use directly with high school students.
    • Teachers Domain has adapted the data from the PBS evolution site slightly to create a lesson plan for teachers with discussion questions about the data
    • There is a good 1995 video of the Grants’ work called “What Darwin Never Saw”, produced by PBS for “The New Explorer” series with Bill Kurtis. Several teacher groups have created lesson plans that follow the video including one from ENSI web and one from the Chicago Academy of Sciences.
    • Finally, for the most advanced students, go straight to some original data and look for patterns and correlations. Prentice Hall has created a lesson plan suitable for AP Biology and college level courses looking at the effect of drought on one species of finch
  2. Another hands-on approach to further investigations of bird beaks is provided in this lesson from TERC. Students use a spring scale to measure the force required to crack a nut with pliers that represent different types of bird beaks.
  3. Finally, there are several videos that provide excellent information on evolution and Charles Darwin.
    • PBS produced a fabulous 7 episode series on evolution. There’s excellent snippets on the evolution of drug resistance in HIV, summaries of Darwin’s work, discussions of evolution and religion, and more. Unfortunately, it is expensive, at $100 for the DVD set alone or $130 for the educators’ set with curriculum.
    • As part of the PBS evolution series, there are several quicktime movie clips that can be viewed over the internet and an associated teacher's curriculum guide with activites and lesson ideas.

8. Bird Beak Buffet - Sources


The Bird Beak Buffet activity is a classic in the teaching of natural selection and evolution. There are hundreds of write ups out there with all sorts of different variations. I first learned about the activity from Kimberly Tanner, currently faculty at San Francisco State University. I found a box of materials to borrow from Chris Giorni of Tree Frog Treks. Then I participated in a workshop with Karen Kalamuck of the Exploratorium Teachers’ Institute.

There are many variations of this activity on the web from many different organizations:

  • USGS
  • The National Aviary
  • Understanding Evolution by the UC Museum of Paleontology has 2 versions of the lesson Clipbirds and Battle of the Beaks.

For background resources on better understanding evolution, nothing beats the Understanding Evolution site from the UC Museum of Paleontology. There you can find everything from evolution 101 to scientific articles to student misconceptions to lesson plans. It’s a one-stop resource for all a teachers’ needs.

Finally, if your school district, administrators or parents opposes the teaching of evolution, see the National Center for Science Education for articles and resources that can help you justify what you are doing in your classroom.

Grade 7
3. Biological evolution accounts for the diversity of species developed through gradual processes over many generations. As a basis for understanding this concept:
a. Students know both genetic variation and environmental factors are causes of evolution and diversity of organisms.
b. Students know the reasoning used by Charles Darwin in reaching his conclusion that natural selection is the mechanism of evolution.
e. Students know that extinction of a species occurs when the environment changes and the adaptive characteristics of a species are insufficient for its survival.

Grade 9-12
7.   The frequency of an allele in a gene pool of a population depends on many factors and may be stable or unstable over time. As a basis for understanding this concept:
a. Students know why natural selection acts on the phenotype rather than the genotype of an organism.
d. Students know variation within a species increases the likelihood that at least some members of a species will survive under changed environmental conditions.

8. Evolution is the result of genetic changes that occur in constantly changing environments. As a basis for understanding this concept:
a. Students know how natural selection determines the differential survival of groups of organisms.
b. Students know a great diversity of species increases the chance that at least some organisms survive major changes in the environment.