Galapagos Finches: Famous Beaks Activity

1.   Battle of the Beaks

Medium ground finches eat a range of food including about two dozen kinds of seeds. These seeds range from small soft ones to seeds in hard shells that are tough to open. One of the toughest seeds is called Tribulus and is about eight times harder to open than the soft seeds that finches also like to eat. Tribulus is able to withstand long periods of drought, unlike the softer seeds. But only finches with the bigger beaks are able to eat these seeds.

Each team will need:

·         Large beak

·         Small beak

·         Food supply: 1 bag containing large and small seeds

·         Metric ruler (mm)

·         Tape

·         2 sheets of paper (“stomach”)

·         Paper plate (“island”)

·         Timer / Watch / Clock

a)    Beak Testing: A Normal Year - There is a mix of large and small seeds

·         Predict which beak will be the better tool for gathering seeds:                                        

·         Prepare a seed supply by placing both small and large seeds on “island” (paper plate)

·         Each beak needs a sheet of paper to act as a stomach for its seeds

·         Each partner needs to practice grabbing seeds with each beak (for just a few minutes)

·         One partner will need to be the beak tester and one will need to be the timer for Test #1, then roles will switch for Test #2

·         For 30 seconds, put as many seeds as possible in the stomach

·         When time is up, count seeds and record data in Battle of the Beaks: Normal Year Chart

b)   Beak Testing: A Drought Year – Mostly big, tough seeds

·         Prepare a seed supply for a drought year by leaving mostly large seeds and only two or three small seeds on the island (return all other small seeds to the food bag!)

·         Repeat steps you did for the Normal Year. Record your data under Battle of the Beaks: Drought Year Chart

c)    Assessment questions:

1.    Which beak size gathered the most seeds in a normal year?                                             

2.    Which beak size gathered the most seeds in a drought year?                                           

3.    Was your prediction above correct?                     

4.    In this simulation, natural selection occurs when the environment favors a certain size beak, therefore causing some birds to survive and reproduce more than others. In a drought year, give a detailed explanation of how natural selection occurred in the finch population.

5.    In a drought year, how would you expect the overall number of finches to change?

6.    Why?

Each team will need:

• 6 Finch Beak sheets (10x larger than life size)
• Metric ruler (mm)
• Pencil

2.   Measure Bird Beaks

No two animals are exactly alike. Differences between organisms of the same species in features like size, color, and abilities are called variations. Usually variations are slight and don’t make much difference. Sometimes a variation will give one creature an advantage over another.

a)    Use the metric ruler to measure the bird beak length in centimeters from the point on the top arrow to the point on the bottom arrow (LOOK AT THE RULER CAREFULLY!).

b)   Record the measurements for each bird on the Finch Beak Measurement Chart in the “Beak Depth Raw Measurement” column. You can identify each bird by its band number.

c)    Because the pictures are 10x the actual size of each finch, beak size is actually a lot smaller. So your units should be in millimeters, not centimeters.  

d)   Calculate the Average Beak Depth and write in the chart.

e)    Assessment Questions:

1.    How many different beak sizes did you find?                       

2.    What was the size (Actual Measurement) of the largest beak that you measured?     

3.    What was the size (Actual Measurement) of the smallest beak that you measured?   

4.    What is the range in beak sizes (Actual Measurement)?                            

5.    Do you think tiny variations in beak size matter for survival? Why or why not?

Finch Beak Measurement Chart

3.  Survival on Daphne Major Island

In 1977 and 1978 scientists recorded 500 days with no rain. Many plants failed to produce seeds as a result. Scientists recorded seed abundance and finch population size in their field notebooks. Seed abundance was calculated by measuring a square meter of ground and then sifting through the soil to count every seed. There was done at many different places to get an accurate count. They repeated seed and finch count every six months. Here are their data:

a)    Follow-up Questions:

a.    During what month and year did the seed supply shrink to its lowest amount?             

b.    During what month and year was the seed supply most abundant?                              

c.    When was the finch population the lowest?                           Highest?                        

d.    What happened to the finch population when the seed supply shrank to its lowest amount? Why?

e.    When the seed supply increased, what happened to the finches? Why?

f.     Beak size is a variation that is passed from parents to offspring. When new generations of young finches were measured in 1978, there were many more young birds with larger beaks. What happened?