April 9, 2013
Monarch Butterflies Rely On Landmarks In Order To Find Their Way
Alan McStravick for redOrbit.com - Your Universe Online
In an article written for redOrbit last month by Michael Harper, the overall population of the Monarch butterfly was predicted to be significantly lower than in years past. It is believed this decline is due to the combination of expanded farmlands and the steady increase in temperature in their migratory corridor.
A new study, led by researchers from the University of Guelph, focused on the migratory corridor followed by these majestic winged creatures. More specifically, the study focused on the butterflies' innate sense of direction and how they arrived at possessing this trait.
The results of the study showed how these insects rely on basic orienteering techniques and the use of landmarks in order to find their way to their wintering sites, thousands of miles to the south from where they begin their journey.
The study, published in the journal Proceedings of the National Academy of Sciences (PNAS), sought to examine the flight patterns of these insects and to determine whether or not the pattern could be affected with geographic displacement.
In addition to researchers from the University of Guelph, other members of the team were from Queen´s University, Germany and Denmark. Contributions from the European collaborators included an analysis of more than 50 years´ worth of migration data with the intent being to learn how the Monarch butterfly is able to find its way for the first time to the wintering habitat in Mexico. Due to the limited lifespan of this insect, the monarch will fly the full migration route only one time during its life cycle.
“To be a true navigator, you need both a compass and a map,” according to Professor Ryan Norris, Department of Integrative Biology at the University of Guelph. “We´ve known for some time that monarchs use external cues, such as the sun and magnetic field, as a built-in compass that can indicate their latitude,” he continued. “But having an internal map requires knowledge of both latitude and longitude.”
The team claims the review of both flight patterns and available migratory data shows when the monarch is blown off course, they will likely use major geographic landmarks to help in funneling them to their destination. When one considers the massive distance flown by the monarch, it is easy to understand why scientists, much like Norris, have considered this butterfly to be a “true navigator”
In order to test this theory, however, the team wanted to learn whether or not the monarch could detect a longitudinal displacement. This portion of the study was led by University of Guelph undergraduate student Rachael Derbyshire, who examined the flight patterns in a funnel on the Guelph campus. The monarchs were then transported west to Calgary to undergo identical testing.
"The monarchs we tested in Guelph flew southwest, in the general direction of Mexico," said Derbyshire. "When we tested them in Calgary, they flew in the same general direction as if they were in Ontario, suggesting that they did not know they had been displaced [by about 1,550 miles]."
The Queen´s University team, utilizing data collected from monarchs that had been tagged and recaptured throughout North America between the years of 1952 and 2004, made an interesting discovery as well. They contend the monarch does not migrate with the use of an internal map. Rather, their travel south to Mexico is dictated by the use of geographic landmarks, such as coastlines and the Rocky and Appalachian mountain ranges.
"Given the challenge of this migratory journey and the fact that these insects are less than a gram, it is a remarkably simple system they used to travel thousands of [miles] to a site they have never seen," said Norris in a statement.
While this team has learned how the monarch is able to migrate, they acknowledge one mystery is still unanswered: how do they pinpoint the exact location in the highlands of central Mexico?
Derbyshire offered her hypothesis, saying, “One possibility we think is likely, and would need to be tested, is that they — like some other migratory animals — use smell to guide them to their final destination.”