Tracking Nesting Activity at Local Heron/Egret Colonies
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, Bob Dyer, 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 pen 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.
Audubon Canyon Ranch has published an atlas on their Web site, www.egret.org/atlas.html , which summarizes the activity at all Bay Area colonies. “The goals of the atlas are to (1) provide a protocol for intensive regional monitoring of heronries, (2) develop current and historical perspectives on the regional, subregional, and local status of herons and egrets with regards to patterns and trends in their nesting abundance and reproductive performance, and (3) consider regional, subregional, and local implications for conservation…The results are based on field observations conducted over the last 15 years and additional data available for previous years as far back as 1967 (38 years).”
Chick count is made at “Nest Stage 4” in the protocol developed by CGRC. This is defined as “adults not continuously at 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|
* 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|
**CGRC not tracking the cormorant chicks.
|Year||Snowy Egret Chicks||Great Blue Heron Chicks|