Bioacoustics Lab- Spring 2011 BRING LAPTOP & HEADPHONES

Transcription

1 Bioacoustics Lab- Spring 2011 BRING LAPTOP & HEADPHONES Lab Preparation: Bring your Laptop to the class. If don t have one you can use one of the COH s laptops for the duration of the Lab. Before coming to the Lab: Download a copy of the free version of Raven Lite onto your laptop, download only the Software & Documentation, for Mac or PC, from the Cornell Lab of Ornithology website: After you download the program (RavenLite10_Executables) you will also have to register for a code to use the program. You will register for the license by clicking on the link to the right of the Raven Lite 1.0 heading ( Get a free license). Fill out the form and an will be sent to you with the registration code, use it and you ll be ready to go. Sound Files: Download from the Biology 129 Website the Sound Files of Odontocetes, Mysticetes, and Pinnipeds that you are going to use during the Lab. Objectives: The purpose of this lab is to describe (quantitatively and qualitatively) the diversity of sounds produced by marine mammals. All analysis will be conducted using the program called Raven Lite 1.0. For each file, you will create a waveform and spectrogram for analysis. For each species you will obtain a variety of measurements including the duration of a call, the peak frequency, the frequency range, and any qualitative descriptions such as downward or upward frequency sweeps (i.e. upward sweep from khz), harmonics, estimated number of animals vocalizing, etc. If there is more than one animal vocalizing, you should also note the overall frequency range of that species sounds. **In your report, you should print out or draw by hand at least one spectrogram in order to illustrate a typical call and how your measurements were made. In addition, you may want to save/print additional graphs or you can draw the sounds from the spectrograms by hand (make sure to label appropriately) to remind you of what you were looking at.

2 To Begin: Double click on the Raven Lite icon. In the pinnipeds folder, open the file titled CAsealion_male.wav. You will have an Oscillogram (or waveform) and a spectrogram, which should look like the following: Waveform: Pressure fluctuations Time Spectrogram: Waveforms show pressure fluctuations from sound over time. Sound travels through air or water as waves of high and low pressure. For example, when your stereo speaker vibrates - as the speaker cone moves out, it pushes air molecules together (higher pressure), and then as it pulls away from the compressed molecules there is a relative decrease in pressure. These pressure waves travel away from the speaker towards your ear. The changes in pressure are what you hear as sound. Relative, ambient (normal environmental) air or water pressure is usually 0 in the waveform. Louder sounds will have much greater fluctuations in pressure (variations above and below 0) than quieter sounds. (For the CA Sea Lion Male plot the ambient pressure level is 128 U). You can use the waveform plot to determine where the sound is the loudest in the call by finding the point were the

3 amplitude it the highest. The command panel in Raven Use the illustration below for working with both waveform and spectrogram plots throughout the lab To play the sound click the icon Use to change the color pattern of the spectrogram (color, grayscale, etc.) This is VERY useful when trying to visualize the calls. Show/Hide Waveform Show/Hide Spectrogram Hide Axes Playing commands Changes speed of playback ( to hear blue/fin whale sounds). 0.5= half speed, 1= real speed, 5= 5x fast, etc.) Zoom in to highlighted area or zoom out. Very useful for taking measurements. Play the sounds a few times and see if you can follow what you hear on the spectrogram (sometimes changing the playback rate helps). In the spectrogram, frequency (Hz or khz) or pitch is shown on the Y-Axis and intensity or loudness of sound is shown with darker shading. Now take some time to play around for a bit with some of the controls on the command panel (highlighting, filtering and listening). Open the sounds of different species, make spectrograms, highlight various calls and listen! **See Tips/Suggestions later for suggestions of how to work with various sounds. Once you feel comfortable using the Raven program, move on to making various measurements on files in the Files for analysis folder. Use your cursor to carefully highlight the calls both horizontally and vertically in the spectrogram. Click and drag in the spectrogram to highlight the frequency range and length of the call you are interested in.

4 + Time: S Frequency: 8465 Hz Power: 62.9 db Parameters to measure To make measurements of what you ve highlighted you will need to use your cursor. Place the cursor in the spectrogram/waveform and see how the different parameters change. Place your cursor at the highest point on the call to determine high frequency or the lowest point to determine low frequency. By moving your cursor in the spectrogram and waveform windows, you will be able to measure different parameters: Time (s or ms), Frequency (Hz or khz), and Power (db) of the sounds you are analyzing. Power is the amount of energy in the sound. To get peak frequency find the highest power and determine where that is along the frequency scale. Use the attached data sheet to make your sound measurements: In some of the sound files there will be multiple signals. Just pick one or more and highlight the horizontal and vertical edges of it carefully. Using your cursor determine: Time (call duration); High Frequency; Low Frequency; Peak Frequency and Power at Peak Freq. For some files, you can also count the number of harmonics. Be careful not to confuse High frequency, which is the Highest pitch of the call, with Peak Frequency- which is the most intense or loudest frequency of the call. For the Frequency measurement, record the range of frequencies used by the species for all signals shown in the file.

5 Tips: Carefully note the units (Hz or khz, s or ms) as these will change between files. Use the comments column to add any qualitative information you think is relevant (i.e. downward sweeps, pulse sound, many/few animals, etc.). Changing the playback rate (speed) can help you hear features of sounds like pulsing (slowing down rapidly pulsed sounds). Try slowing down some of the odontocete sounds. Increase the rate of playback of the blue and fin whale sounds to hear them. Some files are already set at a faster play rate. Watch as the cursor scrolls during playing to determine the speed. Progressively make these sounds slower (and lower frequency) until you can no longer hear them. In real time they are close to or outside of the low range of human hearing. For some files the calls are best visualized with the cool color scheme or standard gama color scheme. Some files contain many animals calling simultaneously, such as the common dolphins. Try to pick one or two whistles out to do your measurements. Use the zoom in feature to get a better image of individual calls and to take your measurements. Lab Report: The lab report should follow the standard format of a scientific paper (Introduction, Materials & Methods, Results, Discussion). Since this exercise is designed to introduce you to field of bioacoustics, as well as improve your quantitative skills, I encourage you to explore various relationships within the data set using graphs or tables. It will give you more to discuss in the synthesis (i.e., Discussion) portion of the report. At least 3 references from the scientific literature are required. Introduction Provide a brief introduction to the topic of sound production in marine mammals. In other words, inform the reader on the main theories of why these animals rely on sound and produce the sounds they do (e.g., communication, echolocation, etc.). This part of the report should also explain the purpose of the investigation and introduce what you plan to compare. Remember: there should be a clear connection between the introduction and the discussion. Methods: Describe the analysis program, how you measured the data, what parameters were measured (peak freq, high freq, etc), and study subjects. Include information on the specific comparisons you made (i.e. calculated means for all Odotocetes). Results: The results section should describe the data in a clear and concise manner. Tables and graphs are always great but think about the relationships that you are trying to describe. Remember to label

6 the axes and do not forget to include the proper units (e.g., Hz or khz, ms) on both graphs and tables. Also, include legends that explain your graphs or tables. At the very least, your report should have a printed or drawn spectrogram illustrating how measurements were made and a table summarizing the results of your analysis. For the more motivated of you- plots showing relationships for things like species/order/suborder vs. vocalization duration, frequency range and peak frequency, etc. will help your grade. Interpretation of the results should be saved for the discussion. Discussion: The discussion section is comprised of a synthesis of your results including your interpretation (i.e., biological) of significant relationships, patterns, or trends in the data. I emphasize synthesis because I do not want you to rehash the results, which is a common mistake. Also, there should be a clear link between the introduction and what you present in the discussion. Below is a list of possible topics for analysis in this lab: Which species or suborder produced the mystery sound and why (based on the summary data from the other species/suborders)? Describe the variation in sound produced between and within groups. Why is there so much variation in sound frequency among all the species analyzed? What is the ecological significance and/or advantage? How do Mysticete sounds differ from Odotoncetes in the parameters measured? How does this relate to their social systems, group behavior, or habitat? Compare the numbers of animals heard in the Odontocete and Mysticete recordings? How does this relate to the differences in the social systems of odontocetes and mysticetes? Compare and contrast the differences in sounds produced by cetaceans and pinnipeds. How do the differences in sounds produced relate to their respective social systems, habitats, or communication needs? Is there a relationship between the power and call duration or peak frequency and duration? How does this change between groups? End the discussion with a solid conclusion (a sentence or two). **These are just a few suggestions for your analysis.