Biology at Sweet Briar

Every autumn, up to a billion monarch butterflies across most of eastern North America migrate south to the mountains of Mexico. By the tens of millions they cluster in forests on a handful of acres. These high altitude sites have few flowers on which butterflies can feed, so the butterflies must stay cold to slow their expenditure of the energy reserves (lipids) they accumulated during their migration. The sites are subject to severe winter storms, and the forest canopy serves as a protective blanket and umbrella. In this project, cold tolerance experiments and lipid analyses will develop a stronger picture of how climate affects both butterfly survival and the rate at which individuals deplete their energy reserves. Detailed studies of microclimate within colonies and in nearby sites not selected by the butterflies will help explain why the butterflies are so selective in their habitat use. Using aerial reconnaissance and satellite imagery, exploration will search for additional overwintering areas in forests identified as having suitable microclimate. Geographic information system (GIS) analysis will integrate all of these components to determine the current extent of suitable habitat, and will quantify how suitable habitat has changed over the past forty years.

Humans are altering the forests where the monarchs overwinter, through logging, fires and ecotourism. The longterm persistence of the monarchs' unique migration depends upon the persistence of appropriate wintering sites. This research has conservation implications, therefore, for scientists, policymakers and citizens concerned about this extraordinary wildlife spectacle.

Overwintering requirements of the monarch butterfly in Mexico: habitat selection versus habitat suitability

PROJECT ABSTRACT