The rookery is located in the Elkhorn Slough National Estuarine Research Reserve. The birds nest in the Monterey Pines rear a freshwater pond. There are historical reports that this area was used in the 1960s by herons but later abandoned for unknown reasons. The current colony began in 1985 with one breeding pair of Great Blue Herons. The numbers gradually increased, and in 1987 Great Egrets joined the colony. By 1993, 27 pairs of Great Blue Herons and 61 pairs of Great Egrets were nesting in the tops of the Monterey Pines.

The rookery in 1993. Photo taken from a helium balloon.

Breeding Season
Each season the Great Blue Herons are the first to arrive (usually from late January to early March). They choose a nest or a place to build a nest at the very top of the trees and forage for twigs from other nearby nests left from the previous season. Both female and male take part in building the nest. Second to arrive in the rookery are the Great Egrets, usually in March. Like the Herons, they look for optimum nesting sites high in the trees, then repair an existing nest or build a new one. Since both species tend to be solitary in the winter months, when they return to mate there is quite an elaborate ritual to establish pair bonding. As far as we know these birds do not mate for life and it is not clear how common it is for birds to return to the same nest or even to the same rookery.

Both species lay their eggs which hatch in 25 to 28 days. Sibling rivalry is intense and usuallly no more than two, sometimes three chicks will survive to fledge depending on the food supply. By the time the chicks reach four weeks old the adults are only at the nest long enough to feed their nagging young.

The young can fly at 7-8 weeks, but will remain at the nest to be fed by the parents for 3-4 more weeks.

The Rookery Cam
In 2000, a camera was installed in the treetops to videotape the egret and heron nests - you can view some of the footage in the Visitor Center. Click here to learn more about this project.

The Future of the Rookery The future of the Rookery is uncertain. As in all heron nesting sites, the trees eventually die from use. The original nesting trees seen in these photos are now brittle and dead. The birds are now starting to nest in a group of Monterey Pines accross the pond. The volunteers at the Elkhorn Slough Reserve are watching this colony closely, counting the nesting birds and studying their behavior. In 1997, another bird entered the picture: Double Crested Cormorants. They usually arrive in June and July to occupy the old Great Blue Heron nests, but this year they showed up much earlier to compete for nests. The Reserve and its partners are doing their part to ensure the protection of these species and to facilitate public viewing of these fascinating birds.

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