Can a Monarch Return Home? Monarch wings vary from pristine, with no scales missing -- seen on newly The Springtime Flight of Monarchs emerged adults (top left); to good, but with some Flying North from nicks on at least one wing (top right); to worn, with by Nathan Miller and Ryan Norris nicks in two or three wings; to very worn, with nicks in all wings.

Migration is one of the most overwintering and breeding sites. In 1878, fascinating behaviors found in nature William Edwards suggested that Monarchs and can be found in nearly every group of migrated south in the fall and that the return organisms and around the globe. Yet despite migration was accomplished by a subsequent our long-time fascination with nature’s long- generation. A few years later, in 1881, distance athletes, remarkably little is known Samuel Scudder suggested that Monarchs about how and why the smallest members migrated south in the winter and that the same following either strategy but some of these Coast towards the Great Lakes region. This of this class, insects, move seasonally. This individuals returned the following spring. individuals had very worn wings suggesting geographic gradient is echoed in the tissues of might seem particularly surprising when we Fast forward just over 100 years and that they may have followed a ‘single sweep’ plants that pick up this isotope from water. In consider the impact that insect migrants have biologists had yet to uncover whether Edwards round trip migration of almost 4000 miles and turn, hydrogen isotopes are incorporated into on our economic well-being. or Scudder was correct. The first study to were, therefore, nearly 9 months old. the wing tissue of Monarchs when they feed For example, consider that, in the southern effectively tackle these hypotheses was by Undoubtedly the reason that the migration on milkweeds as caterpillars. Because wing , the migratory fall army worm Stephen Malcolm and others, in 1993. Armed of Monarchs has proven so difficult to tissue does not change after the adult Monarch moth (Spodoptera frugiperda) causes as much with knowledge of where the overwintering untangle is due to our inability to track such is emerges from the chrysalis, Monarchs carry as $138 million in damage to cropland each sites were located, Malcolm and his team small, short-lived organisms through space an isotopic signature of their birthplace even year, and yet, as with other insect migrants, we formalized these two earlier hypotheses and time. Similar to Malcolm and co-workers, after they migrate hundreds or thousands of know amazingly little about how this species into the multi-generational ‘successive we used chemical markers, in this case, stable miles. This methodology allowed us to capture moves geographically throughout the seasons. brood’ hypothesis (Edwards’ view) and the isotopes of hydrogen, to gain information any Monarch in the Great Lakes region and However, perhaps the best illustration single generation ‘single sweep’ hypothesis about where individual Monarchs were born. determine its approximate birthplace. When of this is North America’s most charismatic (Scudder’s view). By using this technique we aimed to provide we combine this chemical fingerprint with and well-known invertebrate, the Monarch. Malcolm and his team used a chemical additional evidence for either a ‘single sweep’ a measure of age such as wing wear, we get Although the migration of Monarchs has been marker technique that attempted to match the or ‘successive brood’ strategy, while at the a picture of how an individual has moved studied more than any other insect, it was only toxins present in different milkweed species same time providing critical data that could be through space and time. about 35 years ago that the wintering grounds (with different geographic distributions) with used for range-wide conservation strategies in We collected 133 Monarchs from 45 sites of the eastern North American population of the toxins stored in the wings of migrating order to better protect Monarchs across their within , Michigan, Wisconsin, and Monarchs was discovered in dense fir forests Monarchs to determine where a particular entire life cycle. Minnesota from first arrival in May through atop the Neo-Volcanic mountains of central Monarch was born. They discovered that Stable isotopes of light elements such June. Each Monarch was given a wing Mexico by Fred Urquhart and his colleagues. approximately 90% of Monarchs returning as hydrogen are passed up the food web to wear score of 1-5 based on the classification For over a century, Monarchs have from Mexico in spring reach the Gulf Coast, consumers and may be used to provide a developed by Karen Oberhauser of the kept much of their migration a secret from lay eggs, and then die, leaving the northward unique geographic fingerprint in body tissues. University of Minnesota (http://monarchlab. scientists who have been speculating on migration to the first spring generation In eastern North America, hydrogen isotopes umn.edu/lab/research/topics/vitalstats/ how these tiny travelers move between their born from to Florida. The remaining in rainwater become increasingly light (or howtomeasure.aspx). This score was used as a butterflies were unable to be assigned as more negative) as we move from the Gulf method of differentiating between individuals 4 American Butterflies,Summer 2012 5