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Location: Home / Activities / Migration Mania!
Background Information:
Once loggerheads hatch, they face the task of migrating to the ocean and the Sargasso Sea. When they first emerge onto the beach, visual cues such as the brightest horizon initially help the hatchlings find the ocean. Upon entering the water, the hatchlings orient themselves so that they are swimming into the oncoming waves. By now the hatchlings have acquired a preference for swimming in a certain direction, which coincides with the seaward direction. Once they have reached the open ocean, the loggerheads are able to use the earth's magnetic field to determine their approximate latitude.
Loggerheads have an internal compass that is called an inclination compass. Unlike traditional, manmade compasses that distinguish between the poles of the magnetic field (north vs. south), the inclination compass of the loggerhead uses the angles formed by the magnetic field lines and the surface of the earth (see diagram on student page). These angles are called inclination angles and the angle is different at each latitude. The loggerheads are able to distinguish between different inclination angles and therefore different latitudes. This is important because young loggerheads spend several years in the North Atlantic gyre, which is a current system that encircles the Sargasso Sea. Drifting beyond the latitudinal extremes of this gyre can be deadly for the loggerhead.
Activity:
Separate your class into small teams for a scavenger hunt. Give each team the instructions and a compass and have them spend a few minutes learning how to use it. Have all teams start at the same position (same spot and facing same direction) with their first clue in an envelope. Each clue in the scavenger hunt will be directions such as "Take 20 steps NE 70°". The clues should be different for each team. The hunt can be as long or short as you like but each team should find the same number of clues. To ensure that the students are using the compass and not simply looking for the next clue, try to hide the clues (index cards).
Example: If you have a 16x18 ft classroom, have students start facing in from a door way (SE 120°). Additional clues could be: 3 steps S 180°. 7 steps NE 70°. 6 steps SE 140°. 3 steps SW 230°. 5 steps SE 170°. Open spaces are easiest.
Now let's see how well your students can navigate!
Now that you have learned how loggerheads use the earth's magnetic field for migration, let's learn how humans can use it to navigate!
Function and Use of a Compass:
The middle of the earth is composed of iron, which produces a large magnetic field around the earth. A compass is an instrument that uses this magnetic field to determine directions (north, south, east, west). There is a small magnet attached to the needle inside a compass, which causes it to point towards the direction of the magnetic north pole.
The figure below shows the traditional features of a compass.
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Compass housing: it turns and is marked with N,S,E,W and a scale from 0 to 360 ° that represents the degrees around a circle
Orienting arrow: it is part of the housing (moves with it)
Needle: the red end always points towards north
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Use the compass to follow along with these directions for practice:
When using a compass it should be held flat and far away from metal objects such as watches and belt buckles. The compass can be used to determine which direction you are heading and help you go in a certain direction. To determine your orientation (direction you are facing), hold the compass flat with the "direction of travel arrow" pointing away from your body and turn the housing until you line up the "orienting arrow" with the red end of the needle. The "direction of travel arrow" will be lined up with a mark on the housing (ex. 40°, so you are facing NE at 40°). If you want to travel in a certain direction, for instance due west (270°), hold the compass as before and turn the housing so that W (270°) is over the "direction of travel arrow" mark. Now turn your body while keeping the compass flat and pointing forwards until the red end of the needle is on top of the "orienting arrow". Walk in the direction that the "direction of travel arrow" is pointed.
Now try traveling in a few other directions until you are comfortable with the use of the compass.
Activity:
Use the compass to complete a scavenger hunt. Each team will be given a clue to begin the hunt and then each clue you find will have directions to the next. The first team to find all the clues is the winner and experts at using the compass!
Discussion Questions:
- What characteristics of magnetic fields do loggerheads and humans use? Are they different?
- What do loggerheads use the magnetic field for? What do humans use it for?
Challenge Questions: These questions can be answered by further investigation of Earth's magnetic field
- Compasses point to the "magnetic" north pole. Are there other forms of "north"?
- Can magnetic fields change and if so what would happen to loggerheads and humans?
Conclusion: You now know some ways in which loggerheads and humans can use the earth's magnetic field. What other animals do you know that use internal compasses for navigation?
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This diagram shows approximate examples of magnetic field lines (the arrows) around Earth. Notice the angles made by the intersection of these lines with the earth's surface. These are known as the angles of inclination. Traveling north from the magnetic equator (curved line), loggerheads experience increasingly steep angles of inclination (from 0° to 90°).
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This Activity is available as a printable PDF for your convenience.
Migration Mania (Adobe PDF, 163 KB)
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