week of 3/13/02
 
 
 


The Naturalist's Corner
By Don Hendershot
The beautiful and amazing monarch butterfly with its magical, mysterious mass migration every fall has garnered a lot of publicity in recent years. Universities and conservation and civic groups across the country have taken up the banner of researching and protecting this incredible insect.

The annual natural history of the species is quite complex. Here it is in a nutshell: the last hatch of monarchs in late summer across the U.S. and Canada are physiologically different from the preceding two or three hatches. These earlier monarchs follow the pattern of most butterflies — the adult whose evolutionary role is the perpetuation of the species generally has a life span of three to six weeks, just long enough to mate and for the female to deposit her eggs. Some entomologists refer to butterflies as the reproductive stage of a caterpillar.

The last summer hatch of monarchs, however, don’t sexually mature for five to seven months. These are the animals that migrate to Mexico and Southern California to overwinter and begin the northward march the following spring.

Besides the travails that face all wild creatures — getting enough to eat, not being eaten and finding shelter — monarchs face coastal development in California, deforestation in Mexico, and pesticides and urban sprawl across their breeding range in North America.

This winter has been particularly devastating to the population of eastern monarchs that overwinter in Mexico. A January winter storm decimated most of the two largest colonies (Rosario and Sierra Chincua). Estimates from the region report nearly 300 million monarchs lost to the storm. Ecologists and biologists in Mexico believe deforestation was a major contributor to the extensive mortality. The fragmented forest could not provide the needed protection from the inclement weather.

State DOTs (Departments of Transportation) across the country have picked up on the public’s newfound interest in monarchs and butterflies in general and have begun to tout the perceived ecological and environmental benefits of highway beautification projects. North Carolina’s DOT has initiated the Monarch Butterfly Program.

The program, initiated by Voit Gilmore, chairman of former Gov. Jim Hunt’s Clean NC 2000 board, has incorporated three species of milkweed (the monarch butterfly’s host plant) into DOT’s roadside wildflower beds. According to a DOT website (www.doh.dot.state.nc.us-/dp_chief_eng/roadside/Beautification/Butterfly/History.html), “This is the type of program that citizens find interesting and enjoy following ... We hope to see an increase in the number of monarchs in North Carolina ...”

At first glance this appears to be a good plan — beautify the roadsides and provide habitat and food for monarchs and other butterflies. But let us not forget the caveat of Robert Burns — “the best laid plans of mice and men often go awry.”

Dr. Diane Debinski, animal ecologist at Iowa State University, and graduate student Leslie Ries (now at Northern Arizona University) recently studied the effects of roadside restoration in Iowa on butterfly populations. Researchers found that when roadsides were restored to native prairie vegetation and herbicide application and mowing were restricted, butterfly populations increased significantly. The study was guardedly optimistic: “Overall, our results indicate that roadside restoration benefits butterfly populations. More detailed demographic data are necessary, however, to explore the possibility that roadsides are acting as sink habitat for some habitat-restricted species.” Sink habitats are low-quality habitats where birth rate does not equal mortality. Populations cannot persist in sink habitats without constant immigration.

Other negative consequences were also noted. This increased population of butterflies also resulted in increased mortality due to car strikes. The effects of car strikes on populations were not quantified and the report pointed out that while greater numbers of butterflies were killed by autos along restored roadsides, the percentage of mortality (numbers killed relative to total numbers) was greater along non-restored roadsides. Debinski and Ries both believe this phenomenon begs for more research. To date this research hasn’t been done but Ries and Debinski both offered their opinion on the subject.

Ries: “Of course, adding milkweed to the roadside may allow for additional habitat that will allow individuals to be added to the population. But having those attractive flowers on the roadside draws individuals into an area with high mortality risk. The question of whether there is a net gain in individuals due to an increase in host plants or a net loss due to being hit by cars is really totally unknown. My own personal opinion is that they are just as likely to be doing more harm than good. Of course, the busier the road, the more mortality there will be, so placement of the plantings is key. Unfortunately, many plantings are done on highly visible (busy) roads. I think more research should be done before people get too gung ho about plantings that are going to be particularly attractive to butterflies.”

Debinski: “We have data showing that there are significantly higher numbers of butterflies killed on paved vs. dirt roads. So, although highway beautification is a nice idea, it’s probably better to plant native roadsides on dirt roads. However if one has to do such planting on a paved road, I’d advocate for the largest possible width of the roadside ... three or more times wider than average ... Those numbers are not based on data, but on the best guess of someone who has spent quite a bit of time thinking about this.”

NCDOT milkweed sites are almost exclusively along four-lane roads and/or interstates. Locations in Buncombe and Haywood counties include I-40, U.S. 70 and U.S. 74. NCDOT and similar state road departments across the country need to invest more time and research into cause and effect before luring monarchs and other butterflies to road shoulders just a few feet from 60 and 70 m.p.h. autos.

(Don Hendershot can be reached at don@smokymountainnews.com)