This year’s foggy butterfly count day – June 4th, 2016 –  yielded fewer butterflies than usual, though the number of species was around the same. The Common Buckeye was the most commonly spotted butterfly in 2016, with the Cabbage White almost as frequent. These two butterflies accounted for 40% of the individuals seen.

WHAT’S THE BUTTERFLY COUNT?

Each year, the North American Butterfly Association (NABA) sponsors the July 4th series of butterfly counts at locations all across the US. Volunteers go out up to one month before or after July 4th to count butterflies in specific locations. We’ve followed the San Francisco butterfly count since 2010, with a gap in 2015 when we found no published data. (If there’s data available, we’ll be happy to publish it.)

Cabbage White sitting on Oxalis

This year, we’re back with our summary of the results. (The results for earlier years are here: 2010, 2011, 2012, 2013, and 2014. )

The San Francisco count, managed by Liam O’Brien, is tricky; San Francisco gets fog in summer and butterflies tend to lie low on foggy days. The 2016 count, on June 4th, had bad luck with the weather, with a persistent fog and only sporadic sunshine. The spotters were able to find 24 species, the same as in most years, but only 499 individual butterflies.

THE TOP THREE AND THE TOP TEN BUTTERFLIES

The highlights of this year’s observations:

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  Two Acmon Blues

  The Common Buckeye was in first place in 2016 by a small margin of just 3 individuals more than the next closest,  the Cabbage White (102 to 99). It was in the top three in 2014. The Acmon Blue, a tiny blue butterfly similar to the endangered Mission Blue butterfly (and its close relative) came in third.

• The Monarch butterfly showed up again for the first time since 2011.  Usually, these are winter visitors in San Francisco. And the Rural Skipper, which first appeared in our data in 2013, is in this year’s Top Ten. [Edited to Add: They were counted on Angel Island.] However, we don’t read too much into this – the butterflies spotted depend on weather conditions, time of the year (since there can be up to 2 months of difference between a late and early count), and maybe, the number and skill of the observers.

• The Cabbage White has been in the first or second position in the six years we’ve followed the Count. In most years, it’s the top of the chart. (In 2013, it was overtaken by the Pipevine Swallowtail.) It’s probably our most consistently present butterfly, at least in summer. It favors plants related to cabbage and mustard, so the wild mustard in San Francisco is probably good for it.  The table below shows the top three in previous years’ butterfly counts, with the numbers spotted. In 2012, two species tied for the second position, each with 92 individuals seen.

Here’s a graph of the top ten butterflies for 2016’s count, compared with how many were seen in previous years. (This year’s data are in the red bars.) This year, the top ten species accounted for 87% of  the identified butterflies, the highest percentage in 6 years.

THE DATA SET

Finally: for data nerds like us, here is the list of butterflies spotted in each count from 2010 (excluding 2015). It’s interesting to look at each species across the years.

Edited to Add: Some of the changes in species visibility is due to adding Angel Island and Yerba Buena Island as locations to the San Francisco count circle a few years ago. In 2016, three of the species were counted only on the islands: The Pipevine Swallowtail on Angel Island and Yerba Buena (though other, non-count reports say it has been seen on Mount Sutro!); the Common Wood Nymph and the Rural Skipper on Angel Island.