Management Recommendations: Use of Native and Non-Native Trees by Overwintering California Monarchs
In July of 2013, biologists with Monarch Alert completed the following white paper:
Management practices at western monarch butterfly overwintering sites are often based on the “common knowledge” that monarchs “prefer” eucalyptus. Yet whether or not monarchs prefer eucalyptus has never been formally tested, in part because such a test would require that monarchs have a choice (options) and express a preference given those options. A test of the hypothesis is provided here. The study compares monarch tree use versus the tree species availability at five Central California overwintering sites across three overwintering seasons. The results show no support for the hypothesis that monarchs prefer eucalyptus. In fact, when monarchs used a tree species disproportionately given the tree’s availability, they were usually clustered on native conifers rather than on eucalyptus. These findings lead to a recommendation against simply planting more eucalyptus as a habitat management strategy. Instead, the findings lead to a recommendation that overwintering groves be managed to include and maintain a mixture of native tree species such as Monterey cypress (Hesperocyparis macrocarpa) and pitch canker-resistant Monterey pine (Pinus radiata).
This project was funded by the Monarch Joint Venture.