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. The Marin Islands supported large numbers of nesting herons and egrets from at least as early as 1979 through 2015 (Table 1). In 2015, all the nesting Snowy Egrets and Black-crowned Night-Herons abandoned the site before completing the nesting cycle and there were substantially reduced numbers of Great Egrets and Great Blue Herons (Kelly and Fischer 2018). Since the 2016 season, West Marin Island has supported zero nesting herons or egrets. East Marin Island supported only small numbers of nesting Great Blue Herons between 2016-2019. Here I present my detailed observations of heron and egret nesting activity on the Marin Islands in 2020 and 2021
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Jennings, S. 2021. Heron and egret monitoring results at Marin Islands National Wildlife Refuge: 2020 and 2021 nesting season. Report to the San Pablo Bay National Wildlife Refuge. ACR Technical Report 90-3-51 © December 2021. Audubon Canyon Ranch, Cypress Grove Research Center, P. O. Box 808, Marshall, CA 93940