In Search of Monarch Butterflies

By Dylan MacArthur-Waltz,

Pepperwood Visiting Scholar & PhD Candidate, Population Biology, UC Davis

I am a second year PhD student at UC Davis in the Population Biology program. One of my major research interests is understanding how interactions between monarch butterflies and milkweed might be contributing to the population fluctuations that the western monarch population has experienced in the past decade. I was initially connected with Pepperwood Preserve by Shane Waddell, the manager of the UC Quail Ridge Natural Reserve, who suggested that it might be a good place to find research-protected native milkweed in the northern coast range.

I plan to investigate how the timing of monarchs migrating inland corresponds to the timing of milkweed availability in the early spring. Specifically, I’m curious if monarchs might, in some years, arrive to some locations in the northern coast range earlier in the spring than natural milkweed is available. Pepperwood is an ideal location to answer this question since it is in a region of the coast range where monarchs may make their first stop, and since it has natural populations of native narrowleaf milkweed (Asclepias fascicularis).

I will address this question using potted milkweed plants to monitor for the presence of monarchs. I will bring potted milkweed plants into the field in early spring, which I will monitor weekly for monarch eggs and larvae. I’ll also monitor the phenology of natural milkweed plants at Pepperwood. If we observe monarch eggs or larvae on the potted milkweed plants before natural milkweed plants have grown large enough to support a monarch caterpillar, that may be an indication that monarchs are limited by milkweed availability in the early spring, at least in some years. My observations at Pepperwood will be paired with similar observations at two other sites, the UC McLaughlin Natural Reserve also in the north Coast Range, and the Putah Creek Riparian Reserve near Davis, CA.

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