Our late season survey of known Monarch roosting sites was a tremendous success.  A total of 4 brave biking-naturalists arrived by public transit and bike (see Transit and Trails here) in order to visit and record occurrence data at a location with a healthy monarch population.  The site information was corroborated with records at Xerces Society.  Although the Xerces thanksgiving count visited this site in late November, our goal was to observe what the site looked like in late January, 2 months later.  Liam O’Brien was helpful in helping us think about survey logistics and goals.  Thanks Liam!

We observed two areas where tree canopy looked to be beneficial for overwintering.  We recorded GPS location, habitat information, searched for clusters, and counted monarchs observed.  We found monarchs at both sites in reasonable densities – 50 individuals per 10 minute search and 20 individuals/10 min.  We could not locate clustering at either site.   Here’s the Golden Hour modified monarch survey form we used – a very similar original was designed by Mia Monroe, Bay Area monarch expert.


Before the day was over we searched one more site that seemed promising but was never surveyed for monarchs.  This publicly accessible site – on East Bay Regional Park District land – was perfectly situated and seemed to have promising canopy structure.  When we surveyed the site, we in fact observed quite a few monarchs circling overhead!  Closer inspection revealed 3 clusters.  Several more were located by volunteers only a short while later.  We are tentatively identifying this as a new overwintering site, adding to the potential (and occupied) habitat for monarchs in the East Bay.  Results will be reported to Xerces and we plan on surveying this site for the Thanksgiving Count in order to compare its population numbers to other Bay Area populations. 

Thanks everyone who made this possible and especially Tim, Emmy and Ry who surveyed with me!  It was truly a wonderful afternoon of transit, biking, and bay wildlife – capped off with the location of a new roosting site!

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