Audubon Canyon Ranch (ACR) has been monitoring nesting Great Blue Herons (Ardea herodias), Great Egrets (Ardea alba) and Snowy Egrets (Egretta thula) in Picher Canyon since 1967. This colony is located at the Martin Griffin Preserve, on the northeast side of the Bolinas Lagoon, near Bolinas, CA (Figure 1). ACR has also been monitoring nesting herons and egrets at the Bolinas colony site, at the base of the Francisco Mesa adjacent to the Bolinas Channel since 1990. This colony’s subsite, located on the south end of Kent Island at the mouth of Bolinas Lagoon, has also been monitored by ACR since it was founded in 2008.

ACR biologists collect data on: (1) the number of active nests, (2) reproductive success (nest survival rates and the number of chicks fledged from successful nests), (3) the nesting stage (a measure of seasonal timing), and (4) any observed disturbances or potential predators observed or inferred in the vicinity of the nesting site. The tables included in this report contain several variables extracted from the data that is collected each year.