San Francisco Butterfly Count Results, July 2011

The San Francisco butterfly count, led by Liam O’ Brien and sponsored by the North American Butterfly Association, has announced its results. This year, it was held on July 3 on a bright sunny day, compared with last year’s June 7th in cold foggy weather. It paid off in record numbers: The same number of observers as last year (34 people) saw  990 967 individual butterflies, against last year’s 775; and 26 species compared to last year’s 24 (some of last year’s didn’t show up, but some new ones did). The top ten species accounted for 82% of the sightings (85% last year). This year, the count included Angel Island, which accounted for some of the new species.

Spring Azure/ Echo Blue – Katja Schulz Creative Commons

The most numerous species this year were again the Cabbage White (378) and the Anise Swallowtail (110). Both years, these two species accounted for nearly half the butterflies seen (49% in 2011, 48% in 2010).

After that, everything changes:

  • Last year, Umber Skippers were third second most common, but they’re way down the list this year, barely making the top ten.  Instead, the Echo Blue (only 5 spotted last year) and the Common Wood Nymph (none spotted last year) came in third and a close fourth.
  • Similarly, the teams  spotted fewer Acmon Blues and Sandhill Skippers this year, and no Field Crescents.
  • By contrast, they saw many more Red Admirals, West Coast Painted Ladies, Common Checkered Skippers, and Western Tiger Swallowtails.

Could be the weather, the month’s delay, or just random events. O’Brien notes that San Francisco leads the nation’s counts in Anise Swallowtails, which prefer hill tops and use fennel as a nursery plant. San Francisco has an abundance of both — despite fennel being treated as an invasive non-native. (Liam O’Brien keeps the website and blog.)

The graph below shows the totals for 2011 (upper bars, in yellow) and 2010 (lower bars, in orange). If you click on the graph, and click again, a larger version shows up.

[Edited to add: This was edited for minor corrections and to add a picture of the Spring Azure/Echo Blue.]

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