How Do Scientists Study Migration?
Migration Introduction | How
do monarchs know when to leave? | Where do the monarchs
go? | How do monarchs find the overwintering sites?
| How do scientists study migration? | References
| Migration Research Projects
The amazing phenomenon of monarch migration has fascinated scientists for decades.
Many methods have been employed in the attempt to unravel the mystery of monarch
migration, including tagging programs, monitoring programs, and more technical chemical
methods. Many of these programs have involved citizens of Canada, the United States,
and Mexico in a cooperative effort to learn more about this remarkable journey.
Tagging
Dr. Fred Urquhart of the University of Toronto began a tagging
program in the 1930’s. After thousands of tagged butterflies and several decades
of work, the overwintering roosts in the mountains of central Mexico were finally
discovered in 1975. Although local residents had known about the roosts for generations,
no one from outside the area had reported them. This collaborative effort continues
today as we attempt to learn more about this migratory phenomenon.
Dr. Chip Taylor of the University of Kansas has continued the study of monarch migration
through a different tagging program called Monarch Watch. Started in 1991, Monarch Watch is a collaborative
network of hundreds of thousands of students, teachers, volunteers and researchers
dedicated to the study of the monarch butterfly. These participants tag tens of
thousands of monarchs each year throughout Canada and the United States. Through
the recovery of tagged monarchs, we have learned a great deal about the routes monarchs
take and how fast they move.
Monitoring Programs
Other organizations have formed with the goal of monitoring monarch migration in
a way that doesn’t require catching and tagging butterflies. Journey North is one such organization. It was established
in 1991 to with two goals in mind: to improve science and math education and to
study several species of migratory animals. Journey North involves school children
from every state in the United States and 7 Canadian provinces. These students report
their first sightings of monarch butterflies every spring. Through these reports,
we can learn about when and where monarchs travel as they migrate north in the spring.
Texas Monarch Watch is another organization that enlists citizens to collect
data on monarch migration. Dr. Bill Calvert, of Texas Parks and Wildlife, organized
this program in an effort to understand the movement of monarchs through Texas during
their fall migration to Mexico and their spring migration northward. Volunteers
call in reports of monarch sightings, providing information about where, when, and
how many monarchs they have seen. This information helps us learn about major flyways
through Texas and, by comparing sightings over several years with weather patterns,
we can learn about how weather influences monarch migration.
Other monitoring programs include the Monarch Monitoring Project run through the Cape May Bird Observatory
Center for Research and Education and the Western Monarch Migration Project run
by Dan Hillburn of the Oregon Department of Agriculture.
Stable Isotopes
Stable isotopes are different versions of regular atoms that have different masses.
For example, the common isotope of hydrogen has one proton and one electron. The
hydrogen isotope called deuterium also has a neutron, and is almost twice
as heavy as the common hydrogen isotope. Scientists can use these differences between
atoms of the same element to identify the "signature" of the breeding
grounds from which a monarch originated. They can do this because different parts
of the world have different amounts of the various isotopes of a particular element.
Rainfall is the likely cause of the difference in hydrogen isotopes, but other weather
patterns and geology can cause variation in hydrogen and other isotopes. When plants
take up water, they obtain a isotope pattern that reflects that of their geographical
region. When monarch larvae eat milkweed plants, they "inherit" this isotope
pattern as well. Scientists can first identify the isotope "signature"
of various geographical regions, then determine the isotope pattern of a monarch
to roughly determine its origin. (For a more detailed description of how this works,
visit the "Why Files" page on stable isotopes and monarch migration.)
Leonard Wassenaar and Keith Hobson of Environment Canada, Saskatoon, Canada, conducted
a field study in which they collected monarch butterflies from the 13 known overwintering
sites in Mexico and analyzed each monarch to determine its isotope pattern. They
then matched these isotopic patterns with "signatures" they had identified
previously. The found that about half of the 597 monarchs collected originated in
the Midwestern corn and soybean belt.
Continue to: References