|Students investigate how shape and structure of beaks affects the type of food that birds are able to eat.||Materials:
For a class of 30 students (10 groups of 3):
|The Windows to the Universe version of a classic classroom activity.|
|One time 20 min. prep time and 40 minutes class time|
Student Learning Outcomes:
|Discussion with slides and hands-on activity|
- Show images of different types of birds with different beak morphologies and ask students why they think the beaks are differently shaped. Lead students towards understanding that the beaks are specialized depending on the type of food that the birds eat. Ask students to guess how different types of birds (woodpecker, hummingbird, pelican, and others with extreme beak shapes) get food based on the shape of the birds’ beaks. Explain what the word adaptation means and how adaptations that aid survival are more likely to show up in future generations. Explain that in the activity students are about to do, they will each play the role of a bird with a different beak shape.
- Organize students into groups and supply each group with beaks (tweezers, dissection probe, pliers, tongs, spoon, or straws) and a cup. Give each group use a different type of “beak”. Explain that each group is a population (a group of animals of the same species that all live within a particular area).
- Have groups make a loop out of a piece of duct tape to attach the plate to the table (to keep it steady) and fill the plate with “food”.
- Explain to students that they will use their “beak” to collect as much “food” from the plate as they are able to in 30 seconds, placing the food particles into their cup (which represents their bird’s stomach). They must use the beak with one hand only and must not touch the plate or food particles with their hands. (Have students hold their cup or put their free hand behind their back to stop them from using it.)
- Have students:
- Collect for 30 seconds.
- Count the number of different food items they each got into the cup.
- Write their data in a data table.
- Have each group calculate the average (mean) number of rice, seeds, marbles, and marshmallows that their population of birds ate in the 30 seconds.
- Ask one member of each population call out their data as you record it on the overhead, so that the data from the entire class is shown.
- As students look at the
summary data on the overhead, discuss:
- Which type of bird was able to eat the most food particles?
- What type of bird ate the least food particles?
- Which type of food was most difficult for your bird to eat?
- Which type of food was easiest for your bird to eat?
- Do all the birds have the same diet?
- Have students dump all the bird food back into the plastic bag.
- To prepare for the second round of the activity explain to students that that the birds are separated on two islands (with one group of each beak type on each island). There has been a drought this season and most food types have died. The food that is available is different on the different islands. Give half the group the food bags that contain rice, and the other half the bags that contain marbles. Repeat step 5. Did all the birds survive the season of drought? Which birds were best adapted to survive? Were the best-adapted birds the same on both islands?
- Finish with a discussion of the different types of finches on the Galapagos Islands, their different beak shapes and distributions, and the observations of Charles Darwin as he explored the area (see background section below for more information).
During his five-year trip aboard the H.M.S. Beagle, Charles Darwin discovered that birds called finches were found on all of the Galapagos Islands. He arrived in the Galapagos in 1835 and found 13 species of finch living on different islands. The finches were similar in size and coloration, but had very differently sized and shaped beaks. The beaks of these finches were adapted to the island where they lived and the food that they ate.
Darwin believed that the process of evolution took too long for us to observe it happening. But the finches of the Galapagos were an example of evolution taking place and he wrote about them in his book called “The Voyage of the Beagle”. Darwin decided that these finches all used to have bills like other finches, but when they came to live on the Galapagos and started eating different things, their beaks changed over thousands of years. This is called divergent evolution. Since he described the finches, a number of researchers, including Peter and Rosemary Grant (who wrote “The Beak of the Finch”) have traveled to the Galapagos Islands to conduct more detailed research.
Each finch species has evolved according to its particular food source. For instance:
- Long beaks are for probing trees and cacti. Cactus finches have long beaks adapted for reaching into cactus flowers and eating the nectar. Warbler and woodpecker finches have long beaks for probing into trees to find insects and other small animals to eat.
- Thick, wide beaks are for crushing hard seeds. Ground finches have beaks adapted for crushing seeds. Medium finches are better adapted at eating small seeds than large ones, so they are not likely to be found on islands with variation in seed size and large ground finches who are able to eat larger seeds. Wide beaks also allow them to take in more food.
Many of the finches in the Galapagos are not yet distinct species because they are still able to reproduce. However, as they are separated onto different islands, physical barriers prevent groups from reproducing. Different species may develop when a population is divided and then the groups evolve in separate ways. This is called allopatric speciation. If the two parts of the population evolve in different ways and then are able to come pack together (if the geographic barrier is removed), the two populations may compete with each other. Or, they may have developed specializations that allow them to no longer need the same food type or nesting space, so they may be able to live in the same space without competition.
RELATED SECTIONS OF THE WINDOWS TO THE UNIVERSE WEBSITE:
- Diversity and Classification
- Tropical Rain Forest Birds
- Desert Birds
- Tundra Birds
- Charles Darwin
- Understanding Evolution, resources from UCMP