Usually solitary birds, great blue herons and great egrets abandon their private ways during the breeding season, when they nest in colonies in tree tops. Rookeries in the Bay area include Audubon Canyon Ranch in West Marin (opening March 14, 2009), West Marin Islands near the west end of the Richmond Bridge, Stow Lake in San Francisco’s Golden Gate Park, 9th Street at Blair in Santa Rosa, and the edge of the Pescadero Marsh.
The females usually arrive at the colony site a few days before the males in the early spring. When the males arrive, courtship begins with distinctive behaviors (check our our feature on this for more info). Once a female has accepted a male’s overtures, both sexes take part in building a platform-like nest; the male generally gathers sticks and then passes them to the female who places them in the nest. Often the same nests are used year after year.
In April and May the eggs are laid and young chicks emerge. For the first few weeks after hatching, the parents will take turns incubating the eggs and guarding the young, while the other forages for food. The returning parent then regurgitates food into the nest for the chicks to eat. By June and July, the chicks will become increasingly noisy and demanding. The parent will place the food directly into the open bills of the chicks. By mid summer, the parents and young leave to resume their solitary lives.
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Islais Creek Park is the first official San Francisco site on the San Francisco Bay Area Water Trail.