Audubon Canyon Ranch (ACR) has been monitoring the number of nesting herons and egrets at Marin Islands since 1979, and the annual reproductive success of Great Egrets and Great Blue Herons there since 1993. This work is part of an ongoing, regional study of heron and egret colonies in the northern San Francisco Bay area (see previous reports in References Cited).
In 2015, all of the nesting Snowy Egrets and Black-crowned Night-Herons abandoned their nest sites on West Marin Island (Kelly et al. 2015). The cause of the 2015 abandonments is unknown. In 2016, we found no evidence of successful nesting by herons or egrets on West Marin Island; however, seven Great Blue Heron nests were established on East Marin (Kelly et al. 2017). In 2017, no Great Egret, Snowy Egret, or Black-crowned Night-Heron nests were established at the Marin Islands, and no herons and egrets nested on West Marin Island; however, five Great Blue Heron nests were initiated on East Marin Island. In this report, we present our observations of nesting activity on the Marin Islands in 2018.