Tactics and Vectors 98/99
The Challenge of Butterfly Migration
Each year in North America probably more than ten species of butterflies migrate northward from early spring to about midsummer and southward from late summer to fall. With the conspicuous exception of the monarch butterfly, the annual migrations of most of the species go largely unnoticed. Occasionally, a migratory species, such as the painted lady butterfly in California, will achieve such spectacular level of abundance that they cannot be ignored and are reported in media. As soon as the numbers butterflies decline to more normal levels, public interest evaporates and no further notice is taken until the next outbreak. Yet, for those who care to watch, the butterflies are always out there, steadily making there way north or south, as the season dictates.
I have been watching monarch butterflies and other species migrate for over 20 years. My interest and enthusiasm about the phenomenon of butterfly migration stems from two sources, the sheer enjoyment of watching one of the major wonders of nature unfold in front of my eyes, and, as an evolutionary biologist, behavioural ecologist, and glider pilot, from the desire to understand how butterflies manage to do it. Without a doubt, these annual, two-way, migrations are among the most amazing accomplishments of insects. Consider, the monarch butterfly can migrate 4500 km from eastern Canada to their overwintering sites in Mexico. For an animal with a body of about 3 cm (0.03 m), flying a single km represents 1000 m/0.03 m = 33,333.3 body lengths. A distance of 4,500 km is about 150,000,000 body lengths for a monarch butterfly. An equivalent feat for a 1.8 m (6 ft) tall person would be 270,000 km. or about 11 times around the earth. Not bad for a bug weighing about half a gram.Nevertheless, it can't be that difficult. We're talking about an insect. Like all insects, butterflies are strong and resilient, but lack special (i.e. magical) powers and are prone to all the limitations that accompany small body size. Compared to migratory birds, migratory butterflies are much slower, have an inferior aerodynamic design, poor vision, a limited capacity to learn, an inferior capacity to regulate their body temperature, an absolutely ridiculous rate of fuel consumption during powered flight. In short, there seems to be nothing to recommend the butterfly body plan, physiology, and nervous system for task of making regular, long distance, directed, migrations. Common sense alone argues against butterflies even attempting such a difficult challenge. Nevertheless, each year millions of butterflies, who apparently haven't the good sense to recognise their serious design flaws somehow manage to make their way across the continent. Apparently, we're overlooking something important here.
Even if we don't understand how the butterflies manage their migrations, we can be sure of one thing - we are still talking about creatures with the brains of insects. However clever their flight tactics, however mysterious their method of navigation, everything has to resolve to a series of simple rules. Lots of rules, hierarchically arranged and nested sets of rules, but, above all, simple rules. The tiny nervous systems of butterflies just aren't capable of anything else. How long it will take for our far greater and less rule-bound intelligence to figure out their flight tactics and navigation tactics is another question. It may prove to be a bit embarrassing.
Some years ago, from the late seventies to the late eighties, I made observations each year during the late summer and fall migration seasons. I collected data for 4 years in southern Ontario, 3 years in Texas, and, with Wayne Wolf and John Westbrook, for 3 years in Georgia. Finally, after 10 years, many hundreds of hours, and thousands of observations of butterfly behaviour, I really had amassed only 3 data points - one set of observations for the Mississauga region of southern Ontario, a second set for south-central Texas, and a third set for Northwest Georgia. Although the data suggested several interesting hypotheses, none could be tested because of a lack of data from other areas. The problem is simple - not enough hands to carry out the work. If monarch butterflies make major changes in flight tactics and, perhaps, their method of navigation, as they make their way across the continent, field studies had to carried out by an army of the researchers located at a multitude of field sites scattered across Canada, the United States, and Mexico. The small group of academic and amateur researchers interested studying butterfly migration were unlikely to accumulate enough field data to test most hypotheses until well into the next century. We needed a legion of volunteers located all across the continent willing to make a standard set of observations at relatively standardised field sites. The resulting field data would have to be entered in a central databank for examination by any interested parties. In other words, research on flight tactics and navigation of migrating butterflies required the level of organisation and collaboration found, for example, among university ornithologists and birders for migration studies, and among university astronomers and amateur astronomers for comet-spotting. At the time, a convenient, relatively low-cost, means didn't exist for co-ordinating a continent wide research program of field studies on butterfly flight behaviour and navigation. The decades long alar tagging program of the Urquharts' is an example of the enormous amount of sustained effort required to answer the most basic questions about the monarch butterfly migration. Questions such as whether the butterflies actually migrated and, if so, where they spend the winter. Who could have anticipated how much things would change. Now, thanks to the development and explosive growth of the world wide web, and thanks to the pioneering efforts to Monarch Watch, Journey North, and others in pioneering the effective use of email and the Internet for education and research, co-ordinating a continent wide research program has become far more feasible.
Encouraged by Chip Taylor, Lincoln Brower, Wayne Wolf and John Westbrook, I decided last spring to launch Tactics and Vectors as a volunteer research program open to any interested individual willing to stand in a field and record the flight behaviour of migrating butterflies. By focusing on field observations of flight behaviour, Tactics and Vectors complements the research programs of Monarch Watch and Journey North. Although the monarch is my all time favorite butterfly, I expanded the scope to include the other species, of migratory butterflies because: (1) They're out there and always happen to fly by whenever you're standing in a field watching for monarchs, (2) often the other species are more abundant than monarch butterflies, particularly in the Gulf states, (3) they exhibit a different range of flight behaviours than monarch butterflies, (4) they have attracted only a fraction of the research effort (as measured by published papers) that has been devoted to the monarch migration, (5) we are not sure how many of the species considered to be migratory actually are, and how many considered to simply have annual range expansions are actually cryptic migrants, and (5) the most valuable insights on the process of evolution is gained from comparative studies. When we have sufficient field data, comparative studies of the flight tactics and navigation of different species of migrants will allow for tests of hypotheses about the evolution of the migration life history strategy among North American butterflies. I expect that we will find that some species of migratory butterflies have evolved very different solutions to the problem of how to get from here to there. In any case, I intend for Tactics and Vectors to play a significant role as we solve many of the mysteries of butterfly migration. We definitely are going to have a lot of fun along the way.