Heron and Egret Survey

Shollenberger’s heron and egret colony is a successor to a long-established colony which was located in the eucalyptus trees near the wastewater treatment ponds off Lakeville Highway. In 2003 a pair of immature Golden Eagles set up residence near the colony at a critical time when nest building had just begun and scared all the other birds away. Some of the displaced birds may have established the Shollenberger colony, Colony #121, located north of Haystack Landing and across the Petaluma River from Shollenberger Park in the giant eucalyptus trees.

Two more local colonies have been established and are tracked: the Ellis Creek Colony (#40), located in the eucalyptus trees off Lakeville Highway (perhaps a revival of the former colony which was dispersed by Golden Eagles in 2003) and the McNear Colony (#139), located in several trees on the eastern shore of the Petaluma River just south of the McNear Peninsula.

PWA docents Dennis Buss, and Len Nelson are tracking the activity of these colonies for the Cypress Grove Research Center (CGRC) of Audubon Canyon Ranch, which has developed an atlas of all heron/egret colonies in the Bay Area. Once the birds start to arrive in mid-March, the docents take scopes, paper, and pens to the viewing site. Each nest is given a designation while identifying the species occupying it. Every two weeks until late June, they watch for the emergence of chicks.

Chick count is made at “Nest Stage 4” in the protocol developed by CGRC. This is defined as “adults not continuously at the nest (may remain after feeding) and chicks (usually) on nest platform.” Below is a record of chicks produced at Nest Stage 4 in the colonies.

Year Great Egret Chicks Snowy Egret Chicks Great Blue Heron Chicks
2003 32 10 4
2004 48 8 2
2005 58 8 2
2006 50 2 3
2007 25 0 0
2008 71 2 6
2009 63 3 8
2010* 0 0 0
2012 19 0 0

* Early in 2010, a pair of Red-tailed Hawks nested in this colony and the aggressive male chased away all egrets and herons which attempted to nest.

Year Great Egret Chicks Snowy Egret Chicks Great Blue Heron Chicks Double-crestedCormorant chicks
2009 0 0 9 0
2010 063 2 20 3
2011 26 0 11 6
2012 31 10 0 **not counted

**CGRC not tracking the cormorant chicks.

Year Snowy Egret Chicks Great Blue Heron Chicks
2010 15 10
2011 26 7
2012 40 12

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