Monarch Butterflies in Eucalyptus in San Francisco

Like everyone else, we knew that Monarch butterflies visit California’s coast in winter. What we didn’t know was that they’re right here in San Francisco!

Monarch butterflies in eucalyptus, california.

(The picture here isn’t from San Francisco, it’s from a commercial stock-photo site.)


For the past few weeks, Liam O’Brien, San Francisco’s own butterfly watcher extraordinaire, has been on the lookout for Monarch butterflies, especially for clusters. He found a trove of them on the huge old eucalyptus trees of  Treasure Island and Yerba Buena, with the help of a couple of other people who’d spotted them there. (His blogpost about seeing over a hundred of these butterflies, Yerba Buena Island Hopping with Monarchs, advised people who wanted to see them there to take the #108 bus from downtown San Francisco, and look in the eucalyptus trees along the road near the old buckeye grove up from Clipper Cove. He also warned that some areas of the island are restricted to the public.)

And then… he found a cluster in the eucalyptus at Fort Mason. He reports about that is on his blogpost, First Monarch Roost I’ve Seen in SF County.  A video of that cluster in the eucalyptus is up on Youtube. (Scroll down to the comments for a link to the video.)

Then, back on Yerba Buena/ Treasure Island,  he recently counted over 600 of these butterflies, including a cluster. Mostly in eucalyptus.

[ETA: Mr O’Brien, incidentally, does not support our interest in Saving Sutro Forest, which he considers “Sutro’s hideous legacy.” See comments below.]


What’s special about eucalyptus, a tree that was introduced to California only in the last 150 years? The Monarch butterflies, which have been around and migrating a good deal longer than that, couldn’t have co-evolved with eucalyptus. It’s not just familiarity.

Eucalyptus is actually an excellent habitat-tree for monarchs. It’s tall, which keeps them out of the way of ground-dwelling predators such as mice. And it flowers in winter, providing nectar. In fact, eucalyptus is an excellent winter food source for a large number of insects — and for the birds that want either the nectar or the insects supported by these flowers.

Liam O’ Brien, writing in Jake Sigg’s newsletter, notes that one possible reason the eucalyptus is a preferred overwintering site is that they bloom in winter. “ Makes sense,” he says.

Given the huge habitat value of blue-gum eucalyptus, what doesn’t make sense is chopping them down.

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7 Responses to Monarch Butterflies in Eucalyptus in San Francisco

  1. webmaster says:

    Here’s the Monarch butterfly cluster in eucalyptus trees at Fort Mason… found by Liam O’Brien, San Francisco’s own butterfly expert.

  2. Liam O'Brien says:

    I never gave them permission to cut-and-paste and glean facts for their cause.

    [Webmaster: Hi Liam: Thanks for stopping by to comment. We’re not going to change the facts, but since you mind, we’re removing the direct quotes. The information they contain is public. We’ll make it clear you don’t support our position, but the fact is that Monarchs were found in San Francisco in Eucalyptus. (We don’t believe we need permission to “glean facts” or to quote small amounts.)]

    I support all of Craig Dawson’s efforts with Mount Sutro Stewards to restore native habitat and try to do something with that Hiroshima wasteland of euc/ivy dead zone up there that is the hideous legacy of Adolph Sutro. I understand some people find beauty in a euc forest. I do to. When I visit Australia.
    Not when I see native Californian plants hanging on for dear life with a carpet of poisonous euc leaves covering them.

    [Webmaster: We’re disappointed you consider this amazingly lovely forest a “Hiroshima wasteland” or a hideous legacy. Until recently, it was always full of birds and animals. It’s a 100-year-old ecosystem. We respect your right to support Craig Dawson’s efforts to restore the native plants and value California native plants more than the living century-old ecosystem of the forest.]

    Robert Michael Pyle, the godfather of American butterflying, says “Don’t be afraid to tell the whole story” — ok, that’s what I’m doing: Monarchs overwinter in eucalyptus trees. It’s a complicated issue to try to get people to understand. Well, Anise swallowtails host on fennel folks, but I’d never tell anyone to plant it. Like eucalyptus, it aggressively overtakes all other plants. And as we are seeing on YBI and TI, it’s a highly specific covergence of eucs that equate a roost site: formation, height, old growth, available nectar source — that we need to protect – not all the eucalyptus!

    So, let’s let the butterflies dictate the agenda of what they need. If anyone finds a roost on Mount Sutro, I’ll be the first to chain myself to those specific trees, but until then, let’s not exploit this ephemeral’s creature’s life-cycle for our own mixed-up notions of habitat right and wrong. – Liam O’Brien

    [Webmaster: Actually, there’s no evidence that eucalyptus is invasive; it was planted on Mount Sutro, it didn’t invade it. If the trees aren’t there, then new generations of Monarchs would never find it to roost in, so there would be no need to protect the extirpated trees… When a creature has an ephemeral life-cycle, it makes sense to protect the areas it might like, not just the ones where it has already been seen. Can anyone say for sure what the Monarch configuration is? If so, we’d love to see it publicized more widely so that trees in those configurations at least are protected. If most of the eucalyptus in the Bay Area is cut down, would Monarchs necessarily find the few remaining to their liking?

    As for mixed-up notions, we’re often puzzled when people who love wildlife are blind to the importance of lush growing plants, bushes, and trees as habitat. It would seem that the preference for “native plants” seems to trump every other consideration. We do not say this specifically with reference to your words, but generally about those who oppose our support for functional habitats rather than idealized reconstructed ones. Like you, we think we should tell the whole story.]

  3. milliontrees says:

    Since Mr. O’Brien urges us to not be afraid to tell the whole story, we shall oblige.

    Mt. Sutro, like all eucalyptus forests, is not a “wasteland” or a “dead zone.”
    Professor Dov Sax (Brown University) tested the claim of native plant advocates that the eucalyptus forest is a “biological desert” while a student at UC Berkeley. He studied the eucalyptus forest in Berkeley, California, and compared it to native oak-bay woodland. He found little difference in the species frequency and diversity in these two types of forest.
    He studied six forests of about 1 hectare each, three of eucalypts and three of native oaks and bays. The sites were not contiguous, but were selected so that they were of similar elevation, slope, slope orientation, and type of adjacent vegetation. He conducted inventories of species in spring and autumn. He counted the number of:
    • Species of plants in the understory
    • Species of invertebrates (insects) in samples of equal size and depth of the leaf litter
    • Species of amphibians
    • Species of birds
    • Species of rodents
    He reported his findings in Global Ecology and Biogeography (“Equal diversity in disparate species assemblages: a comparison of native and exotic woodlands in California,” Global Ecology and Biogeography, 11, 49-52, 2002):
    “Species richness was nearly identical for understory plants, leaf-litter invertebrates, amphibians and birds; only rodents had significantly fewer species in eucalypt sites. Species diversity patterns…were qualitatively identical to those for species richness, except for leaf-litter invertebrates, which were significantly more diverse in eucalypt sites during the spring.”

    Since Mr. O’Brien has a special interest in butterflies, he would be wise to inform himself of the work of Professor Art Shapiro. Art Shapiro (UC Davis) has been studying California butterflies for over 35 years. His observations as well as the work of other scientists have informed him that “…the extensive adoption of introduced host plants has clearly been beneficial for a significant segment of the California butterfly fauna, including most of the familiar species of urban, suburban and agricultural environments. Some of these species are now almost completely dependent on exotics and would disappear were weed control more effective than it currently is.” (SD Graves and AM Shapiro, “Exotics as host plants of the California butterfly fauna,” Biological Conservation, 110 (2003) 413-433)

    He explains that this is particularly true on the coast of California because this is where the highest concentration of introduced species of plants is naturalized and the butterfly population is less diverse because of the cool, foggy climate. There are apparently few non-native plants in the desert and alpine regions of California and so butterflies in those regions have not had the opportunity or need to adapt to new plants.

    The case of the Anise Swallowtail Butterfly is not an isolated example of a native butterfly that uses and is sometimes dependent upon non-native plants in California.

    We’re glad that Mr. O’Brien is not afraid to tell the whole story and we hope he will inform himself of the whole story by reading the work of these scientists who assure us that the animals, and insects—including butterflies—that live in our cities have long ago adapted to what grows in them. We should do the same: learn to live with what grows here.

  4. Keith says:

    I don’t think I need his permission to point out that the photo of monarchs on Albany Hill on O’Brien’s website also shows the monarchs in eucalyptus. Also interesting in that photo is that someone is obviously eating the leaves of those eucalyptus–contrary to the usual claim that eucs are useless because native animals can’t use them.

  5. milliontrees says:

    In Jake Sigg’s most recent Nature News, Mr. O’Brien suggests that folks organize to save the eucalypts on Yerba Buena Island that are being used by over-wintering Monarch butterflies. Mr. Sigg demurs. After all, they ARE eucalypts.

    Mr. O’Brien says, “almost no Monarch overwintering sites are protected – other than the ones in parks.” We wish that were true. Unfortunately it is not. Monarchs are not necessarily protected in parks either.

    One of the biggest populations of over-wintering Monarchs can be found in eucalypts at Pt Pinole Park, one of the properties of the East Bay Regional Park District. The Sierra Club has been advocating for years to destroy all of the eucalypts at Pt Pinole. The Park District has acquiesced with plans to destroy most of the eucalypts there, but the Sierra Club is not satisfied. They want them ALL destroyed.

    As for the Monarchs at Pt Pinole, this debate between the Park District and the Sierra Club is moot. The Park District’s plans to thin the eucalyptus forest to a small fraction of its current density will be the end of the Monarchs at Pt Pinole. The Monarchs require a dense forest to provide the necessary protection from the cold and wind. They will find another place or they will die. Since eucalypts are being eradicated everywhere, the chances that they will find another place diminish as we speak.

    When will bird and butterfly lovers learn that their alliance w/ native advocates is not helping the creatures they love?

  6. Pingback: The Plants that Monarch Butterflies Need | Save Mount Sutro Forest

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