Glencoe Life iScience: Animal Diversity, Student Edition

Book Preface

Although the beautiful black and orange wings of the monarch butterfly are a common sight during summer in the United States, as fall and colder temperatures arrive, the butterflies disappear. Each fall they begin a seasonal migration. Scientists have had some success in unlocking the mystery of monarch migration through the use of scientific methods. Through this example, you can see how each step of this scientific method contributes to reliable results that can lead to better-informed conclusions.
The monarch population that lives west of the Rocky Mountains flies to the coast of California. The eastern population of monarchs flies to the mountains of central Mexico. Sometimes they travel up to 145 km per day. Some eastern monarchs, such as those living in southern Canada, fly more than 3,200 km to reach their winter home.

Navigation
Just as astonishing as the distance traveled by these insect voyagers is their ability to find their way. Since no butterfly completes the entire round-trip, the butterflies cannot learn the route from others. So, how do butterflies that have never made the trip before find their way from Canada and the eastern United States to Mexico? This is the question that some entomologists—scientists who study insects—set out to answer

One of the first hypotheses about how eastern monarchs navigate was that they use the Sun as a guide. Researchers based this hypothesis on other research, which showed that some migrating birds rely on the Sun to guide them. However, this failed to explain how the butterflies find their way on cloudy days.

Magnetism
Scientists later discovered that the bodies of eastern monarchs contain tiny grains of a naturally occurring, magnetic substance called magnetite. Magnetite was used to make the first directional compasses. From this discovery, scientists developed a hypothesis that butterflies use an internal magnetic compass to help them plot their route. University scientists tested this hypothesis by performing an experiment. They caught some eastern monarchs during the fall migration. They divided the monarchs into three groups and exposed each group to different magnetic fields. The group exposed to Earth’s normal magnetic field flew to the southwest, which is the correct direction for eastern monarchs to migrate. Those exposed to the opposite of Earth’s normal magnetic field flew to the northeast. Finally, those exposed to no magnetic field fluttered about randomly.

Final Conclusions
After analyzing the results, the researchers concluded that eastern monarchs use an internal magnetic compass to navigate from Canada and the eastern United States to Mexico. However, most researchers also believe the butterflies also use the Sun and landmarks, such as mountains and rivers, to make their incredible journey

Science
Scientists learned about the migration of eastern monarch butterflies by starting with questions such as “Where do monarchs go each fall? How do they find their way there?” Scientists use experiments and careful observations to answer questions about how the world works. When you test an idea, you are doing science.

Life science is the study of living things. In this book, you will learn about the diversity of animals and their adaptations and behaviors, such as migration, that enable them to survive. Scientific Methods Researchers used scientific methods to learn about how eastern monarchs navigate. Scientific methods are a series of procedures used to investigate a question scientifically.

Identifying a Question
Sometimes, scientific methods begin with identifying a question, such as “Where do eastern monarch butterflies go every autumn?” After one question has been answered, others often arise. When researchers discovered eastern monarchs migrate to Mexico, the next question was “How do the butterflies find their way?” Forming a Hypothesis Once a question is identified, scientists collect information and develop a hypothesis or possible explanation.

They might read the information available on how birds migrate and use it as a basis for the hypothesis that eastern monarchs use the Sun to navigate. This idea, however, failed to explain how the butterflies find their way on cloudy days. As a result, scientists developed another hypothesis—eastern monarchs use an internal magnetic compass that enables them to maintain a course in a specific direction.

Testing the Hypothesis
Scientists test hypotheses to determine if they are true or false. Such tests often involve experiments, such as one where eastern monarchs were exposed to different kinds of magnetic fields.

Analyzing Results
During experiments, scientists gather information, or data. Data about the butterfly experiment included the direction that the butterflies were flying when captured, what type of magnetic field they were exposed to in the experiment, and how they reacted to that magnetic field.

Drawing a Conclusion
After data have been collected and carefully analyzed, scientists draw conclusions. Sometimes the original hypothesis is not supported by the data and scientists must start the entire process over. In the case of the eastern monarchs, researchers observed how the butterflies reacted to the magnetic fields and concluded they use an internal magnetic compass to navigate. Just how the butterflies use Earth’s magnetic field to find their way is another question for scientists to answer using scientific methods