Tuesday, October 03, 2006

Monarchy in southeastern Missouri

They must have come in the cover of night. Sunday afternoon, the asters and goldenrods were covered in checkered skippers and cloudy sulphurs--both smaller, pale-colored butterflies who have been around all summer. By Monday morning, there were no fewer than 40 monarchs floating outside the window and mobbing the tiny patch of goldenrod next to my office door. The annual monarch migration is underway in southeast Missouri and it's nothing less than spectacular. For two days I have felt like Ferdinand the Bull, trying to get work done but continuously distracted by the bright colors flying around.

East of the Rocky Mountains, the monarch (Danaus plexippus) follows a migratory path to a forested sanctuary in Michoacan, Mexico. Eight other species of butterfly make annual migrations, including the lovely Painted Lady (Vanessa cardui), but they only have a lifespan of one week and don't have a directional preference during their migration. The other migratory species all fly in a general southern direction to stay ahead of the frost line but with no real wintering grounds in mind. Only the monarch lives 7 months to see a full migration in its lifetime. While most monarchs live on average 2 months, the ones that make the round-trip migration live longer than any other butterfly. The migrating generation doesn't reproduce until it leaves the mountains in Mexico and finds an area that has milkweed growing in it to lay its eggs.

Researchers still have a lot of questions about the monarch migration. How do successive generations "know" to return to a single wintering spot in the highlands of Mexico? In the past few years, researchers have offered tagging kits to butterfly enthusiasts, which include little stickers with numbers and codes to be affixed to the delicate wings of monarchs. Reports of tagged monarchs have resulted in a lot of interesting information regarding the migration, but not enough information to determine exactly how they make the annual migration.

Monarchs have had a hard time the past few years. Continuous drought in the upper Midwest has interrupted the bloom cycles of the host plant, milkweed (Asclepias sp.), making it harder for the butterflies to find it. Just about every habitat has a milkweed associated with it. There's the delicate swamp milkweed (A. perennis) that my boss simply adores, there's one that grows on glades (A. verticillata), there are several prairie species and the ones that show up in ditches throughout the Midwest. In the Deep South, the natural habitat has been so greatly degraded that the only milkweed that really performs well is an introduced Brazilian species, A. curassavica. The drought has reduced almost all of the watering and nectar sources for monarchs, including the flowering milkweeds. If it's not drought impacting the habitat, it's herbicide treatment of preferred weedy areas. The weedy wildflowers and grasses are a proverbial goldmine to monarchs and most other butterflies. Finally, in Mexico, illegal deforestation of oyamel fir trees has impacted the wintering monarch population. The butterflies depend on the foliage of these trees to protect them on cold and windy nights. Recent reforestation projects in the area have proven successful and the 2005-06 populations are healthier than the 2003-04 populations. The current, exceptional drought in the Midwest, Texas and Mexico could have a serious impact on the monarchs this fall. The recent rains in southeast Missouri, however, have caused a robust bloom of asters and goldenrods and certainly given the butterflies lots of room to mine for minerals in pools of mud.

There aren't a lot of weedy areas left in southeast Missouri; even turnrows are sprayed with RoundUp down here. I let my yard grow up with "weeds," of course, much to the dismay of colleagues. I recently helped a friend with a butterfly monitoring program and realized that even though the survey area was an exquisite forest on the Mississippi River, the best butterfly habitat was found along the edges of the forest where thistles and goldenrods bloomed. The patch of woods I work in is rich with asters and goldenrods. Both of these are plants a lot of people mow over, treat with herbicides or just ignore. Their prolific populations are essential to the migrating monarchs. There are over ten species of asters and four species of goldenrods native to southeast Missouri. This diversity might account for the high numbers of monarchs in the area right now; I honestly haven't seen this many since I left New Orleans, a town rich with weedy lots and butterfly gardens. Almost everyone in New Orleans had at least a handful of nectar sources growing in their yards. The tropical climate down there allows for a lot of wildflowers, zinnias and butterfly host plants.

While I am not getting a lot of work done in the woods because the monarchs and migratory birds are so distracting, I'm enjoying seeing how the butterflies relish the plants most people hate. Funny, that during the monarch migration the weedy, prolific bloomers are at their peak. How that intricate web of nature seems to work...

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