Every year billions of insects, birds, and bats fly from central and South America through Mexico up into the United States and Canada. These migrations are one of the most spectacular and visible phenomena of the natural world. Yet factors that initiate and guide these migrants year after year remain poorly understood, especially for insects. One factor that is known to be important, but not well understood, is the direction and strength of prevailing winds, which are largely determined by atmospheric circulation cells. These cells are dominant environmental drivers impacting not only the pattern of prevailing winds, but also the location of ecological biomes across the Earth. The largest of these cells, called the Hadley cell, operates in the tropical zone approximately from latitude 30°S to 30°N. In this cell, winds rise around the equator and then move both North and South at higher altitudes. As they fall to the ground closer at the edge of the tropics, they bring dry air, but also potentially carry the migrants. Monarch butterflies (Danaus plexippus), the best-known insect migrant, overwinters in Mexico, near the focal point of the Hadley cell updraft and migrates North to lay eggs in Texas, near where the Hadley cell subsides. Yet the connection between Hadley cell and monarch migration to date has not been explored. This study will examine the role of the Hadley cell in the annual migratory dynamics (timing and success) of eight species of butterflies, including monarch, that migrate across Mexico and into the US. This work will develop migration model / educational modules that will be applicable for understanding aerial migrant across the globe. Results will be shared among the stakeholders and public through the three-butterfly websites run by the research team, and the results will also be incorporated into the regular lectures on quantitative ecology at Georgetown University.
Migration accounts for massive transfers of nutrients and biomass in ecosystems worldwide and also provides a key strategy for species survival. Yet migration is a particularly challenging phenomenon to study due to its large spatial extent. Given the importance of environmental drivers such as temperature, precipitation, and wind for migration, environmental change may have substantial impacts on animal migration, particularly for insects. This study will develop a framework using global atmospheric circulation cells to understand long-distance migration. Models will be validated using data from seven sites of the National Ecological Observatory Network (NEON) in the southwestern US and also with data from several citizen science butterfly monitoring networks. Further, the team will use climate models to project these patterns into the future under different climate scenarios. The study?s specific objectives are to quantify the degree to which the largest atmospheric circulation cell, the Hadley Cell, underlies the mechanistic dynamics of departure, migration and arrival for insects migrating from the tropics to the temperate zone. This work will model migration of eight butterfly species, three of which show classic round-trip migration (e.g., monarch) and the remaining five migrate one-way only in the fall.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
