Academic journal article The Science Teacher

Awesome Aggregations: Students Study Overwintering Biology and Behavioral Ecology with Model Monarch Butterflies

Academic journal article The Science Teacher

Awesome Aggregations: Students Study Overwintering Biology and Behavioral Ecology with Model Monarch Butterflies

Article excerpt

Insects are a natural choice for studying behavioral ecology in the classroom--they are easy to obtain, maintain, and manipulate. Unlike competition and predation, however, the concept of group living does not translate well to small-scale experiments involving only a few individuals. How can we use inquiry to examine why animals live in groups? The answer is to use models, which are more feasible than working with hundreds of test subjects. This article describes a Standards-based directed inquiry into overwintering biology and behavioral ecology titled "Awesome Aggregations" that high school students can carry out with models of monarch butterflies.



Monarch overwintering

Every fall, the entire eastern North American population of monarch butterflies (Danaus plexippus) escapes harsh winter conditions by migrating up to 4,830 km to central Mexico (Oberhauser and Solensky 2004). The high-elevation fir-pine forests that serve as overwintering sites for monarchs have relatively stable microclimates; even so, freezing temperatures are common and northern winter storms occasionally bring snow and rain.

Due to their small body size, adult monarch butterflies can remain unfrozen (i.e., supercooled) at temperatures as low as -14[degrees]C (Anderson and Brower 1996). Monarchs with water on their bodies freeze at a much higher temperature than dry monarchs; ice crystals on the body of a wet monarch induce freezing within its body fluids by a process called inoculative freezing (Larsen and Lee 1994). Unlike some other insects, monarchs cannot survive freezing.

How do monarch butterflies stay dry during winter storms? First, monarchs aggregate in very high numbers: approximately 20 million butterflies may aggregate on less than 1,000 trees! The structure of monarch colonies has evolved, in part, to protect butterflies from wetting (Anderson and Brower 1996). Monarchs on the inside of clusters stay drier than butterflies on the edge. Second, dense tree canopy acts like a blanket and an umbrella for aggregating monarchs (Anderson and Brower 1996). Intact canopy reduces radiational cooling of monarchs (i.e., the energy radiated by monarchs is bounced back to the butterflies by tree canopy rather than lost to the open sky), intercepts precipitation, and reduces dew formation.

Unfortunately, the fir-pine forest required by monarchs for overwintering is restricted to only five mountain peaks and is being rapidly destroyed. Between 1971 and 1999, 44% of the forest within three protected butterfly reserves was thinned or cleared. When the forest is thinned, the protective function of the canopy is reduced and butterflies may be forced to aggregate on the ground or on low bushes. The combination of intense logging and a severe winter storm resulted in an average colony mortality of 75% in January 2002 (Oberhauser and Solensky 2004). Furthermore, climate change models predict that central Mexico will get wetter and less hospitable for overwintering monarchs (Oberhauser and Peterson 2003).


Model butterfly construction

To prepare for the Awesome Aggregations activity, teachers should construct model butterflies from goldenrod indicator paper, available at most office product stores, which turns bright red when a basic solution is applied. Teachers should photocopy eight butterfly templates (Figure 1) onto sheets of goldenrod paper and give these templates to students for preparation of the models (Figure 2). Instead of using valuable class time to cut out and fold the butterflies, we recommend that students work on them as a homework assignment or when they have finished in-class work ahead of schedule.

Inquiry activity: Awesome Aggregations

To put this activity in context, teachers can start with a brief slide show describing the life cycle and migration routes of monarch butterflies. …

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