The Monarch Migration

What You Can Expect to See… and What You Can’t

By the Friends of the Monarch Trail

Aug. 30, 2016

     The migration of the eastern North America population of monarch butterflies is one of nature’s greatest marvels. Creatures that have dispersed throughout the summer from the East Coast, as far north as Nova Scotia, and to the Rocky Mountains in the West, as far as southern Alberta, and all the territory in between, begin to congregate and move south. Some will fly as far as 3,000 miles to reach their common destination in central Mexico. Along the way, the monarchs tend to form larger and larger groups and roost communally in trees, as they do here every year.

     As we celebrate the beginning of the migration on the Monarch Trail on the County Grounds, many people ask us questions such as: “When will the monarchs be here?” and “How many will there be?” and, most vexingly, “Why didn’t I see any?”

     The short answer is: We don’t know. No one knows. To avoid disappointment that you may have already missed “the migration,” or being dismayed that we can’t offer you a specific date and time to see it, please consider the facts – what we do know.

The migration of monarchs from and through our region of southeast      Wisconsin begins, by general consensus of experts and longtime observers, on about Aug. 26. It can last six weeks or more, throughout September and into October. We have had few migrants leaving the County Grounds as late as the last week of October. In some years, we have seen as many as a dozen separate roostings of monarchs. In some years we have had only one or two flocks. Any of these groups may be as large as hundreds or even thousands; they may be no more than a handful.

     “The migration” is not a one-day event. There is not a single flock that moves through all at once. They come in trickles and streams, and sometimes in droves. But any single migration event is impossible to predict. Imagine trying to predict exactly when you will see a flock of migrating geese fly overhead. It could happen at any moment over several weeks. It is no different with monarchs. Weather patterns hundreds of miles from Wauwatosa may affect the monarchs’ movements. Changing winds may impede them or speed them on their way.

     We can tell you that the peak of the migration, and your best chance to see large numbers on the County Grounds, is usually in mid-September. A warm day with a fair wind out of the northeast might give you an advantage. But even armed with that hope, any chance of seeing a large gathering of monarchs is just that – chance. The monarchs may know where they are and where they are going, but we don’t. Your best bet is to visit frequently in late afternoon or early evening throughout the migration season and hope for the best while willingly accepting the possibility of disappointment.

     Think about it – wouldn’t it be tedious if nature were always perfectly predictable? We can predict that monarchs will come to the County Grounds, because they always have. But we can’t predict exactly when, and that, for us, has always made the excitement feel new when they do arrive.


Good luck!

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