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!
(The picture here isn’t from San Francisco, it’s from a commercial stock-photo site.)
MONARCHS AMONG US
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.]
MONARCHS LOVE EUCALYPTUS
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.