Experiment: Are we there yet? Test how migratory birds navigate

Can you imagine traveling over 3,200 kilometers (2,000 miles) to a brand-new place for the first time, without a printed map or directions to get you there? That is exactly what Gambel’s white-crowned sparrow (Zonotrichia leucophyrs gambelii) does!

This sub-species of sparrow migrates from breeding grounds in Canada and Alaska down to warmer wintering grounds in California and Mexico. From years of observation, biologists have learned that these sparrows are solitary migrators. Rather than migrating in flocks, each bird takes off on his or her own and navigates his or her own route between the breeding and wintering grounds. This includes the juvenile birds who are hatched in the breeding grounds and need to find their way to wintering grounds that they’ve never seen before, without a parent’s help!

Imagine you were out hiking in the wilderness where there were no guided trails. You’d need two tools to help you navigate: a map and a compass. The compass would tell you in which direction you were headed, and the map would tell you where you were in relation to the location you wished to go. For example, if you were lost and trying to get back to camp, the compass would tell you what direction you were walking, but not which direction camp is in. But a map would tell you that.

For example, let’s say the map showed that the camp was north, but without a compass, you wouldn’t know which direction you were facing. Some migratory animals may be able to “get away with” just using a compass: If they know the wintering grounds are south of them, they can simply move south. However, these animals will not be able to reach the wintering grounds if something moves them off the normal migratory pathway — such as getting blown several hundred kilometers (miles) to the east or west of the migratory route by the wind. But if these animals also have a map that allows them to migrate, they will know that they are off-course and can correct for that movement.

Scientists have long speculated that in order to complete its long migratory journey, Z.l. gambelii must use some sort of internal map and/or compass. But do juvenile birds making their first migration and adult birds who have made the journey before rely on the same navigational methods? Or is the internal map of an adult bird modified by their previous journeys?

In an effort to answer these questions, a research team coordinated by Dr. M. Wikelski conducted an experiment. They displaced 30 migrating Z.l. gambelii (15 adults and 15 juveniles) from their migratory route in Sunnyside, Wash., all the way across the country to Princeton, N.J. They fitted the birds with radio transmitters and released the birds. Using antennas, both on the ground and on airplanes, they tracked the signals from each bird’s transmitter to determine their flight paths as the birds resumed their migration.

This system of using radio transmitters and antennas to gather data about animals out in the wild is known as radio telemetry. You might have seen it used on nature programs where they attach radio collars, which hold large radio transmitters, to mammals like bears or wolves. The transmitters you’ll be studying in this project are similar, just miniaturized so that they can be attached to small birds, such as the 18-centimeter-long (7-inch-long) Gambel’s white-crowned sparrow.

What were the results of this high-flying experiment? Did the birds head toward their normal wintering grounds, or were they disoriented after being displaced by more than 3,200 kilometers (2,000 miles) from their typical migration path? Did adults and juveniles behave similarly or differently? And what does this experiment tell us about how the birds navigate — does it seem likely that they have an internal compass? How about an internal map?

This project will give you access to the raw data from the experiment and you can analyze the data and answer these real-world research questions yourself!

Terms and Concepts

• Gambel’s white-crowned sparrow (Zonotrichia leucophyrs gambelii or Z.l. gambelii)
• Sub-species
• Migration
• Juvenile
• Compass
• Radio transmitter
• Antenna
• Radio telemetry
• Latitude
• Longitude
• Cardinal direction
• Stacked bar chart
• Statistics
• Chi-square test
• Categorical data

Questions

• What are the current theories about how birds navigate? Do all birds appear to use the same method(s)?
• How does radio telemetry work?
• What are some applications of radio telemetry?
• How do you read and use longitude and latitude coordinates?

Resources

This resource offers more information about radio telemetry:

• Wikipedia Contributors. (2008, November 12). Telemetry. Wikipedia: The Free Encyclopedia. Retrieved November 12, 2008.

These resources can help you understand what the Chi-square test is and how to use it:

• Lemmon, A. R. (n.d.). Statistics: Chi-Square Test. Retrieved November 21, 2008.
• GraphPad Software Inc. (2005). Chi-Square Example: Compare Observed and Expected Frequencies. Retrieved November 21, 2008.

Use the program listed below to complete the mapping portion of this science fair project:

• Google. (n.d.). Google Earth. Retrieved November 24, 2008.

Other migration and animal tracking data sets are publicly available at various websites; here is one such example:

• National Park Service, U.S. Department of the Interior. (n.d.). Fly Away! Instructional Resources. Retrieved November 24, 2008.

Materials and Equipment

• Computer with Internet access
• Google Earth, a free mapping program: http://earth.google.com
• Lab notebook
• Graph paper

Experimental Procedure

Familiarizing Yourself with the Data and Data-Analysis Program

Before you begin analyzing the data, it’s important that you understand what type of data you’re looking at and how to work the Google Earth program, which you’ll use to help analyze the data.

1. In this project, you’ll use real data collected from radio-tagged birds. Open this bird migration dataset containing data for the Gambel’s white-crowned sparrow. Familiarize yourself with each column of data.
   1. Age: Birds are either adults or juveniles.
   2. ID: Each bird has its own unique identification number.
   3. Release Location: For experimental reasons, all the adult birds were released from the Princeton Airport, and all the juvenile birds were released a couple of miles away at Princeton University’s Stony Ford Research Station.
   4. Date and Time: This column shows the date and time that each position reading was taken on. The time is in 24-hour (military) clock time. For example, 6:00 is 6 a.m. and 18:00 is 6 p.m.
   5. Position: The geographic location of the bird is reported as longitude and latitude coordinates. Make sure you understand how to read these coordinates. Consult the references in the Resources section for more information on longitude and latitude. Some birds have more data points than others, because working in the wild can be difficult and not every single movement of each bird can be tracked.
2. To analyze the data, you’ll need to download a free version of Google Earth. Google Earth is a program that allows the user to customize their own maps. You’ll use it to mark the flight paths of each bird in the migration experiment.
   1. Follow the onscreen instructions to install this program.
3. Once Google Earth is installed, play around with it to figure out how to find a location, mark that location, select colors for your place-markers and measure the distance between two locations or along a path.
   1. Consult the Google Earth User Guide for help.

Mapping the Data

Once you’re familiar with what each piece of data represents and how to use Google Earth, you’re ready to create a map showing the flight direction of each released bird.

1. Using Google Earth, create a place-mark at the location from which each bird was first released.
   1. Since all the adult birds were released from one location (Princeton Airport) and all the juvenile birds were released from another location (Princeton University’s Stony Ford Research Station), you’ll only need to create one place-mark for each bird age group.
   2. Make all place-marks that correspond to data about adult birds one color, and all place-marks that correspond to data about juvenile birds another color. This will make it easier to quickly spot any patterns in the mapping data. Note: You’ll want to apply this same color-coding to all the place-marks and lines in subsequent steps, too.
   3. Give the place-marks informative labels, like “Adult release point” and “Juvenile release point” so that you don’t forget what they represent.
2. For each bird, put additional place-marks at every position the bird was tracked to, including the last position the bird was tracked to.
   1. Give each of these place-marks an informative label, like “Bird 1, 9/22, 20:17,” which includes the bird ID, as well as the date and time the bird was at that location.
3. Using the Google Earth path tool, draw a path connecting all the place-markers for each bird.
   1. The paths represent the observed flight path of each bird. There should be a total of 30 paths, one for each bird.
4. Now create hypothetical travel lines (one from each release point, using a color-coding method for the lines that makes sense to you), showing which direction the birds would be heading if they were going each of these places:
   1. Traveling back to Sunnyside, Wash., the place from which they were originally dislocated.
   2. Traveling along the same cardinal direction (south), as if they thought they were still in Sunnyside, Wash., and needed to fly south to reach their normal wintering grounds in southern California and Mexico.
   3. Traveling to their normal wintering grounds. Since the actual wintering grounds are a range encompassing much of southern California and Mexico, use San Diego, Calif. (which is on the border of California and Mexico), as an approximate location for the wintering grounds.

Analyzing Your Data

1. Look at the Google Earth map you created. Did the birds in the experiment appear to be flying in the general direction of any of the hypothetical travel lines? Or were the birds completely disoriented and flying in directions not predicted by any of the lines?
2. To quantify your results, make pie charts or a stacked bar chart showing the percentage of birds traveling along each hypothetical travel line.
   1. You may need to add other categories to your chart if you find that for some birds, none of the three hypothetical travel lines describes their flight path. For example, you may need a category for birds that did not resume migration and instead appeared to stay at the release site.
3. Look at the charts. Did the adult birds and juvenile birds behave similarly or differently? To confirm your conclusion, you can use a statistical test called the Chi-square test.
   1. The Chi-square test is often used on categorical data to decide if the data observed during an experiment met the expected results. Categorical data is any data divided into named groups — for example, the groups in your chart — as opposed to represented by numerical measurements, such as a person’s age or height.
   2. In this science fair project, there is no clear expected result. So to compare the adult versus juvenile bird categorical data, you’ll need to choose one bird age group to take the place of the expected result. For example, you could frame the question as: “Do the juvenile birds behave in the same manner as predicted by the adult birds’ behavior?” In this case, the adult birds would represent the expected result, and the juvenile birds would represent the experimental results.
   3. Use the references in the bibliography to familiarize yourself with what the Chi-square test is. Then use the online Chi-square calculator from GraphPad to help you calculate the result.
4. Based on your data analysis, what can you conclude about the navigational tools of Gambel’s white-crowned sparrows? Do they have internal maps? How about internal compasses? Does having completed a migration previously (as is the case for the adults, but not the juveniles) alter their navigational abilities?

Variations

• If fewer data points were collected, would you still come to the same conclusions? Try creating a second map where only the first and last position points are used to create a flight path for each bird. How do the two maps compare?
• Try analyzing other publicly available bird migration data sets (or any other species of animal you’re interested in and can find a tracking data set for). The types of questions you can ask depend on the type of data collected. One possible data set to examine is a multi-year project tracking the migration of golden eagles from Denali National Park and Preserve to their wintering grounds and back again.

This activity is brought to you in partnership with Science Buddies. Find the original activity on the Science Buddies website.