Butterflies of San Bruno Mountain

Ever since I knew I would be coming out to the Bay Area I’d been checking the listservs and NABA Recent Sightings to see what butterflies might be flying in this year’s fairly early spring.  I had a couple of targets — Sonoran Blue, which I had tried for last year on a similar work-related trip with colleague Mark Adams, Margined White, Large Marble if it was flying, California Tortoiseshell, and the endemic race of Moss’s Elfin on San Bruno Mountain, the San Bruno Elfin.

I frankly don’t remember what we did before the Internet.  With a few days of research, I narrowed down locations, times, directions and general behavior for all the target species.  As it happened, they pretty much all resolved onto one man:  David Rawlinson.

David was very generous with advice before I got out to California, providing a great deal of critical information that would make my visit both enjoyable and productive.  And he gave me great hope for finding four of the five targets — sadly, it appears Large Marble isn’t out yet, and my California sojourn ends Wednesday morning!

My first stop would be San Bruno Mountain to look for San Bruno Elfin, which haunts the rock faces where its caterpillar hosts — succulents, Dudleya farinosa and Sedum spathulifolium — are not uncommon on some of the trails at the mountain summit.  The elfins lay their eggs on these host plants, which will soon be sending up flower stalks, and the caterpillars feed on the flower buds and seed capsules.  And the adult’s favored early spring nectar source, desert parsley (the species on San Bruno is Lomatium utriculatum), occurs on many of the slopes. 

Fresh off my non-stop flight from DC, I picked up a rental SUV and headed the 15 minutes north on 101 from SFO to San Bruno Mountain State & County Park (with an obligatory LepLunch at Daisey’s Taqueria in Brisbane, of course!).  I arrived at the summit around 2 pm with only a vague notion of the location of the prime spots for elfins from a previous post of David’s on NorWestLeps, and pretty much frittered away the afternoon stumbling around all the wrong places for San Bruno Elfin.  Plus, like eastern elfins, San Bruno Elfins seem to take a powder after mid-morning or at least be harder to find.  So I turned up nothing that resembled an elfin.

But … the sunny sky, calm winds, and warm temps (low 70’s) did provoke a good bit of hill-topping by other species.  Near the parking lot at the summit I watched two fresh Anise Swallowtails zipping around the high spots, and about a half mile out on the Ridge Trail I ran into a veritable multi-species dogfight of West Coast Ladies, Red Admirals, and — target acquisition #1 — several California Tortoiseshells.

2016 Feb. 23 California Tortoiseshell, one of several seen hilltopping in mid-afternoon at the summit of San Bruno Mountain.

2016 Feb. 23 California Tortoiseshell, one of several seen hilltopping in mid-afternoon at the summit of San Bruno Mountain.

This was a dearly bought picture, as I stepped backwards to get it into focus and into a deep hole that nearly broke my leg.  Limping back to the car, I did manage a couple of Gray Hairstreaks and a few more Anise Swallowtails, but no sedum and no Dudleya.

San Bruno Elfin would have to wait.

This entry was posted in endangered species, Field Trips/Annual Counts, general butterfly news. Bookmark the permalink.

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