Students learn how spectrograms represent sound variation, and then examine the sounds of owls for traits that might be useful in determining evolutionary relationships. They compare these traits to morphological ones (appearance and plumage), ultimately coming up with their own evolutionary hypotheses to test using multimedia from the Macaulay Library. more ...
Learning how to construct and interpret phylogenetic trees is one of the most important skills for students studying biodiversity and evolution. Most trees that students encounter are based on DNA sequences or morphological traits, but there are other characters that can be useful for studying relatedness. In this investigation, students study bird calls and songs, and use them to infer relationships and to think about the function of calls in the life history of birds.
This investigation is composed of three semi-independent parts, which escalate in complexity and in the independence of thought required from the students. Parts 1 (“What You See is What You Hear”) and 2 (“Owls in Trees”) teach students skills that they can apply to fully inquiry-based projects in Part 3. Instructors can choose to omit Part 3 if time does not permit the entire investigation. Part 1 equips students with the skills required for independent navigation of the Macaulay Library, so it can be used as a stand-alone lesson to prepare them for other projects that use the library’s resources.
The Macaulay Library is an ideal place for students to explore natural history and make their own observations and measurements. It is large enough that students can find their own topic or taxon of interest within it, allowing them an authentic scientific experience as they use its data to test their hypotheses. (see Instructor Guide for more details)
- Which traits are useful in classifying organisms, and when would one type of trait be more useful than another?
- Learn how to use and explore the Macaulay Library at the Cornell Lab of Ornithology (Part 1)
- Analyze owl calls to define phylogenetic characters, and use these characters to build a phylogenetic tree (Part 2)
- Compare the calls tree to morphological and DNA trees, and discuss the reasons for their similarities and differences (Part 2)
- Develop hypotheses about how bird calls relate to bird life history traits, and test their hypotheses via independent research using the Library (Part 3).
- Computers (one per pair of students, plus computers available for students to use outside class) with Internet access, and QuickTime and RavenViewer installed. Computers must be able to play sound, either through speakers or through headphones.
- A similarly configured computer for the instructor, with a projector for demonstration. This computer should be audible, so the instructor can demonstrate sounds for the class.
- Optional (useful in a large class): headphones for the computers, one per student. It would be helpful if two students could listen at the same time.
- Student worksheets
- Scratch paper
- For Part 1: prizes for the highest score on day 2 (optional)
- For Part 2: printouts (preferably in color) of the Student Sheets and Owl Morphology Sheets
- For Part 2: (ready, but not distributed) printouts or overheads of the Species Key and molecular phylogeny of Owls (from Wink et al. 2009)
This investigation is designed for undergraduate or high school students who are familiar with the idea of phylogenetic trees. The tree-building exercise may be made more or less sophisticated, depending on the prior experience of the students. As written, it requires only an intuitive approach to grouping by similarity, but it is easily adapted to require students to apply formal algorithms of parsimony (for example) to the character matrices.
This investigation would be appropriate for a general biology class (perhaps in the behavior, ecology, or evolution curriculum), an introductory course on evolution, or a course on animal behavior.
See Materials for specific computer requirements to conduct the investigation. Information on installing the free QuickTime plug-in for RavenViewer can be found at: http://macaulaylibrary.org/help/ravenViewer/index.do.
Part 1: What You See is What You Hear
Intended for two consecutive class periods. 30 minutes in the first class, then 30 minutes in the second class after the students have completed the at-home assignment.
Part 2: Owls in Trees
Variable depending on how rigorous you wish the phylogenetic approach to be, and how detailed you wish to make the discussion. A reasonable estimate would be two hours total for sections 1 and 2 (separable into two class periods), with section 3 assigned as homework.
Part 3: On Your Own
Variable. Students could design their own investigations in subsequent class periods, or on their own as an end-of-semester assignment.
Part 1: What You See is What You Hear
- Understand what a spectrogram is and how to interpret it
- Be able to navigate and explore the Macaulay Library
Let students know that they will need to be able to use the Macaulay Library for a homework assignment. Begin by giving students a tour of the Library (http://macaulaylibrary.org). Take requests from students, typing in the names of birds or other animals that they’d like to hear examples of.
Introduce students to the idea of a visual representation of sound by demonstrating a RavenViewer spectrogram, including how to "zoom in" on a spectrogram for fast and detailed calls. (See Instructor Guide, or http://macaulaylibrary.org/help/ravenViewer/details.do)
If time permits, have students explore the library and the viewer in pairs on their own computers.
Finally, give students the homework assignment, including information on the best way for them to turn it in (email, a web drop-box, etc.). (See Student Sheets)
Before class, prepare a sound-matching game based on student explorations of the database. (For details, see Instructor Guide)
When the students arrive, hand out the copies of the recording pictures. Play each recording in a random order (WITHOUT projecting the spectrogram), and have students quietly assign it to the spectrogram they think it fits best.
When you have finished, go over the game sheets as a class and give a prize to the student(s) with the highest score.
Part 2: Owls in Trees
This part of the investigation is meant to give students practice in building and using phylogenetic trees, using an unusual set of character traits (owl calls). More broadly, it invites discussion of the important question of what constitutes a good phylogenetic character for a particular group of species. DNA sequences for owl species are not yet easily available, which provides an opportunity to experience and discuss when morphological or behavioral traits might be used as evolutionary characters instead. (See Instructor Guide for more details)
- Use the Macaulay Library to listen to the calls of ten North American owls, and decide on characters to use to describe the calls
- Build a phylogenetic tree of the owls based on their calls
- Build an independent tree of the same owls based on morphology
- Compare the two trees and discuss the similarities and differences
- Compare both trees to a DNA sequence tree
- Analyze and write up their findings.
Section One: Calls
Decide in advance how long you want students to take on this part of the investigation, and how many characters you want each group to come up with. Share these expectations with the students. Most students find this activity fun, so if you have the time (e.g., devoting an hour to section one), it is rewarding for students to be able to take the time to enjoy the sounds and debate the merits of different characters.
Divide students into pairs, one pair per computer, and hand out the Owls in Trees Student Sheets. Have students work through the first section of the sheet: listening to the ten owl calls, deciding on characters, and scoring the characters in the table provided.
The URLs for the owl calls are anonymous; they do not indicate the species names of the owls, so students will not have clues about which species are in which genus. (See Instructor Guide for more information)
When students have finished their trees, reunite the class for a discussion. Solicit characters that students used, and write these on the board. Have groups come up and write their trees on the board, indicating the character transition points. Groups with different character choices and/or character weights will produce different trees, and this enables a good discussion of what makes a good character. Ask student groups to explain their reasoning. Ask the class for opinions on which groupings they think are the most likely to be correct, having seen various trees, and which characters they think are the most likely to be informative. If possible, leave the trees on the board while students work on section two.
Section Two: Morphology
Pass out the owl picture/description sheets to the pairs of students.
These owls are lettered rather than numbered, so students will not be able to tell which photo and description corresponds to which call. As before, they are also anonymous, with no species names. Have students develop and score characters in the same pairs as before, and make trees. This will take less time than section one, because they have practiced the skill and because looking at pictures is faster than listening to calls.
Once students have finished, reunite the class again and have them draw the new trees. Discuss differences between trees. Was there more agreement between trees for morphology than there was for calls?
Reveal the number/letter/species-name correspondence at this point, handing out the Species Key. Discuss.
Finally, give out the DNA tree from Wink et al. 2009. Discuss the discrepancies between gene trees (presented in this phylogeny) and species trees, and how ancestral polymorphism can result in misleading results. Students will have a bias toward trusting the DNA tree over the morphological or call trees; discuss this preference and whether it is merited.
Section Three: Discussion Questions
Assign the discussion questions found in the Student Sheets as homework.
Part 3: On Your Own
In section two, the class discussed whether calls or morphology make better characters for owls. Ask the question: What about owl ecology might make calls a better character than it is in parrots? This discussion should lead to some hypotheses (see Instructor Guide for examples). From these ideas, have students develop hypotheses that can be tested in other bird groups using the Library’s recordings of songs and calls. Students will work in groups of three to test these hypotheses. Where molecular phylogenies are available, you can help students find and interpret these to help with their investigations of the sounds.
Part 1 can be assessed on a credit/no-credit basis depending on whether students submitted a recording with setting and playback information as assigned. Students could grade their own quizzes to get formative feedback on how well they matched the sounds, or exchange with others for grading.
See Instructor Guide for discussion questions to go with Part 2: Owls in Trees. We recommend using this discussion to probe for understandings and misconceptions about the merits and difficulties of creating trees based on different types of data, rather than explicitly focusing on how accurate or not the student trees were.
You can assign the discussion questions found in the Student Sheets as homework after Part 2.
For Part 3, depending on the desired end result of student investigations (in-person presentations, short reports, etc.), if time allows, you could develop a grading rubric as a class, and use it to conduct peer review on each others' methods and conclusions. See Instructor Guide for a list of relevant articles from the primary literature you might wish to suggest to students as they work on Part 3.
All images courtesy Macaulay Library, Cornell Lab of Ornithology. Unless otherwise indicated, the owl descriptions are from the Cornell Lab of Ornithology’s “All About Birds” website: http://www.allaboutbirds.org.
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