Lab: The Beaks of Finches
Introduction
Environmental conditions act as selecting agents because they select organisms with the
most beneficial traits to become the parents of the next generation. Within a species,
individuals with variations that make them better adapted to their environment will survive
and reproduce in greater numbers than those without such adaptations. Observations
have shown that the offspring of better-adapted individuals inherit many of their parents’
favorable variations.
Finches are small birds found in many locations throughout the world. Charles Darwin used
the numerous finch species on the Galapagos Islands as evidence of natural selection. The
great variety of finch species found on the Galapagos is thought to be due to the isolation
of bird populations on the islands with different kinds and amounts of food. Seed-eating
finches exhibit a great number of differences in beak shapes and sizes. During ongoing
competition for resources, some finches are more successful and become more numerous,
while less successful finches decrease in number.
In this laboratory activity, you will work with different tools that will serve to model finch
“beaks.” The seeds provided represent finch food on a particular island. You will compete
with other “finch” species to see which “beak” is best adapted for obtaining a specific
food.
Before the Lab
1. Examine the different tools (“beaks”) and seeds provided. Predict which “beak” will
be the most successful at picking up the seeds. Give reasons for your choice.
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2. Predict which “beak” will be the least successful at picking up the seeds. Give
reasons for your choice.
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Directions
You will be trying to transfer the seeds from the island (the tray) into your stomach (the
petri dish.) We will do this several times. Each time, your finch must eat at least 15 seeds.
If you do not eat 15 seeds during the round, then your finch dies.
If your finch dies, you must be reborn as a new finch. Any finch that survives can
reproduce and give you a beak of their type.
During the first trial, only one student will be eating from each tray. However, during the
second trial (the next year) there is a drought. Because of this, there is less food
available for the birds! In this trial, two students will be eating from each tray.
The next year is even worse!! This time, three students will be eating from each tray.
Data
What tool is your beak?
Your Data
How many seeds did you
eat during the trial?
Did your finch live?
Round One:
Round Two:
Round Three:
1. Was your original beak successful? ______________________________
2. If so, what made it successful? If not, what made it unsuccessful?
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Class Data
Tool Type
How Many
Were Alive
at the
Beginning?
How Many
were Alive
after Round
One?
How Many
were Alive
after Round
Two?
How Many
Were Alive
After Round
Three?
Analysis
1. Looking at the chart above, which beak type was the best at surviving?
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2. Looking at the chart above, which beak type was the worst at surviving?
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3. After a million years, which beak type would you expect the birds to have?
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Why? ___________________________________________________
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4. Name three traits other than beak characteristics that could contribute to
the ability of a finch to compete successfully.
a.________________________________________________________
b.________________________________________________________
c.________________________________________________________
.
5. Were the beaks that were successful in the first trial still successful once
we added competition? Why or why not?
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.
6. Why were there fewer survivors at the end of round three?
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Use the following chart to answer the remaining questions.
7. Predict which species of finch would be most likely to survive if the weather
on the Galapagos Islands gradually changed and the seeds available to the
finches became larger with heavier coverings. Support your answer with an
explanation. ________________________________________________
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8. One island is populated by two species— small ground finches and small tree
finches.
a. What two types of food would you expect to be available on this
island? Support your answer. ______________________________
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b. Would you expect the two species to compete for food on this island?
Support your answer. ___________________________________
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c. How might the two native finch populations be affected if several
dozen sharp-billed ground finches were to migrate to the island and
survive? Support your answer. _____________________________
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9. Explain how an island could support large populations of both large ground
finches and small ground finches. ________________________________
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.
10. Would you expect an island to be able to support large populations of both
small ground finches and sharp-billed ground finches? Why or why not?
(HINT: your answer should include the word “competition.”)
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11. What has this lab taught you about evolution that you didn’t know before?
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