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Saturday, November 23, 2013

On their way to the desert?

In the last post I mentioned some interesting bird sightings from Doran Beach on 21 November 2013.  That's not the only thing that caught my eye that day.  As soon as I started walking onto the beach, I noticed butterflies flying by coming in off the water or flying parallel to the shore. 

It seemed late in the year for a notable butterfly movement along the coast.  But when I left Bodega Bay and felt the very strong offshore winds that were especially apparent inland, I wondered if the weather conditions had something to do with dispersing butterflies showing up along the shore.

Some of the butterflies would land on the sand and start to bask in the sun:



Others would bask on upper beach plants:


The view above displays the characteristics of a Painted Lady (Vanessa cardui).  [For more about how to identify this species, see this post from last October.]

Many of the butterflies were stopping to nectar on flowering Sea Rocket (Cakile maritima):



In a Field Guide to Butterflies of the San Francisco Bay and Sacramento Valley Regions, Shapiro and Manolis write that Painted Ladies overwinter in deserts along the U.S.-Mexico border and then move northward in late winter and spring (e.g., late February-late April).  They breed along the way, and their offspring move further north.  Southbound individuals appear in our area in late August and "may straggle even into early December."

So from this picture of their life cycle, the butterflies observed along the coast this past week are probably late southbound migrants on their way to the desert.  Indeed, some of them were quite tattered and I wonder if they'll make it to their final destination (see below)?


I don't know if other people have kept track of the phenology of southbound Painted Lady movements along the coast, or whether it's tied to offshore winds, but I'd love to hear back from other folks with more information. 

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