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.
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 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. |