Type of Document:
This report presents an overview of the 2013 nesting season at the Picher Canyon heronry at Martin Griffin Preserve, Stinson Beach, CA, as well as at its nearest-neighbor heronry at the southwest end of Bolinas Lagoon. We provide background information about Great Egret nesting activity across the northern San Francisco Bay area and discuss important aspects of egret nesting biology. We identify factors that may have contributed to nest failure in Picher Canyon, including disease, predators, disturbance, and food availably, and evaluate the extent to which each of them may have affected the heronry. The underlying processes that led to the nesting decline are potentially complex. Therefore, the responses of the nesting birds may not reflect the consequences of a single underlying cause but, rather, the effects of multiple causes with varying direct or indirect influences. In this report we use available information to consider all possible influences. We conclude that disturbance to the colony by avian predators is the most probable explanation for the colony decline.
Millus, S. A., Kelly, J. P. and T. E. Condeso. 2013. An assessment of the 2013 decline in Great Egret nesting in Picher Canyon. ACR Technical Report 1967-1-2 © September 2013, Audubon Canyon Ranch Cypress Grove Research Center P.O. Box 808, Marshall, CA 94940