Hundreds of thousands of bats emerge from a hole in the ground, and scientists with high-speed video cameras are there to make sense of the overwhelming spectacle.

About This Video

Grade level: 6-13+
Length: 7.5 minutes
Next Generation Science Standards: MS-LS2.A, MS-LS4.C, HS-LS2.D, HS-LS4.C


Every summer evening, deep in the Hill Country of central Texas, hundreds of thousands of Brazilian free-tailed bats (Tadarida brasiliensis) pour from the mouth of a limestone cave. The pungent smell of guano and the rush of sound and air from so many wings beating at once is an experience that truly overwhelms the senses. Then, just like that, it’s over—in a matter of minutes, members of the entire colony have emerged from the cave and disappeared into the dusk for their nightly foraging flight. To the naked eye, in real-time, the colony exodus is a blur of wings and bodies moving too fast to track. Yet somehow, the entire colony manages to exit the cave, night after night, without traffic jams or (many) casualties. How do they achieve this incredible feat? Scientists Nickolay Hristov and Louise Allen set out to answer this question. Using the latest generation of high-speed video cameras, they have captured these events—and interactions among individual bats—in spectacular detail. Now, frame by frame, they are discovering that it’s not always necessary for nature to come up with the perfect solution—just one that’s good enough.

Video Discussion Questions

  1. What is it about the behavior of the Brazilian free-tailed bats that is so extraordinary?
  2. Why do you think the bats come out of their cave all at once instead of coming and going one at a time or in smaller groups?
  3. What characteristics of these bats can scientists see by studying them using high-speed video?
  4. What kind of flying are bats well adapted ('optimized') for? What kinds of flight behaviors are they not well adapted for?
  5. What are some of the challenges the scientists in this video face in their research? What research questions are they trying to answer?
  6. Does evolution lead to perfect systems or structures? Why or why not?
  7. What kinds of things are scientists learning about what influences bats' flight behavior coming out of the cave? What are some questions they have that they don't yet know the answers to?
  8. Do bats ever crash into each other?
  9. What are some things you were able to see happen in the time lapse videos that you probably wouldn't otherwise be able to see?

Classroom Activities to Accompany This Video:



Have students choose a time lapse sequence from this video and watch it without sound. In their science notebooks, ask students to write down:

  • 3 things they noticed or observed
  • 2 questions they have or things they wonder about, and
  • 1 thing they learned

On the board, draw a table with three columns labeled 'I noticed...', 'I wonder...', and 'I learned...'. Have students discuss their observations, questions, and knowledge gained, and write these things in the appropriate column on the board. In addition to the following questions, you can use the About This Video section to engage your students in a deeper dive into the Brazilian free-tailed bat ballet:

  1. What is the purpose of time-lapse video?
  2. How can time-lapse video be used in research, particularly in bat behavior research?
  3. What bat behaviors can you observe with the time-lapse video that you wouldn't necessarily be able to observe otherwise? 
  4. What other applications of time-lapse video can you think of?

Does Natural Selection Lead to Perfection?


One common misconception about evolution is that evolution always results in progress. A related misconception about natural selection, a mechanism of evolution, is that natural selection produces organisms that are perfectly adapted to their environment. Bats are a great example of how natural selection produces organisms that have traits that are 'good enough' for survival.

Before engaging in this activity, students should have a basic understanding of evolution and natural selection as a mechanism of evolution. You can find a variety of lessons and educator resources on this topic at UC-Berkeley's Understanding Evolution website.

Focus Question: Does natural selection result in organisms with perfect adaptations?

  1. Write the Focus Question on the board, and give students 3-5 minutes to individually reflect on the question in their science notebooks.
  2. Give each group of 3-4 students one topic to research from the following list: Giraffe recurrent laryngeal nerve, Human larynx and esophagusIrish Elk antlersVertebrate eye
  3. In their groups, students should create a presentation to share with their classmates that uses what they learned from their research to answer the Focus Question.
  4. Keep a class data table on the board that summarizes the findings of each group. After each group has presented, have a class discussion about the findings:
  • How would you answer the Focus Question based on what you've learned? Is there any more information you'd like to have that would make you more sure of your answer?
  • What might cause organisms to not be perfectly adapted to their environment? Can an organism survive and reproduce in an environment that it isn't perfectly adapted to?
  • Can you think of other examples in addition to the organisms you learned about today that support your answer to the Focus Question?

Teacher note: Before students dive into their research, make sure they're familiar with how to find and evaluate credible sources on the internet.

Photo credit: Eric Kilby

Video Credits

Produced by Spine Films, this video appears in bioGraphic, a magazine powered by the California Academy of Sciences to showcase both the wonder of nature and the most promising approaches to sustaining life on Earth.

Additional Resources

Video: Biodiversity and Natural Selection
How does natural selection give rise to new species? Learn how environmental conditions play a critical role in determining if an individual will survive and contribute its genetic information to the next generation in this video from the California Academy of Sciences in partnership with Khan Academy.

Lesson: Color Vision Genetics Evolution Simulation (Grades 7-12)
In this lesson, students will participate in a natural selection simulation, flipping pennies to mimic the probability of passing on certain traits. The traits are the three genes for color-vision, found on the X chromosome. In the simulation, students will simulate six generations of primates, and track how the gene pool changes over time. The activity loosely mimics some of the mechanisms that led to the evolution of our own improved color vision.

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