Slender, blue-gray birds up to five feet tall, great blue herons (Ardea herodias) live all around San Francisco Bay. With half its height in its long legs, this majestic bird wades in the Bay’s shallow tidal waters, often standing silent and unmoving. Then, with a sudden thrust of its sharp beak, the great blue heron stabs a fish and swallows it whole.
Sometimes the fish is larger than the heron’s own head, and a visible lump goes in stages down the bird’s long, s-shaped neck. Great blue herons also eat small land animals. If an unwary pocket gopher sticks its head out of its hole, a heron can grab it and eat it in one gulp.
There are about 600 great blue heron pairs that nest around San Francisco Bay, including on Alcatraz, at Don Edwards National Wildlife Refuge in the South Bay and even at Stow Lake in Golden Gate Park. With a six-foot wing span, great blue herons rise into the sky with grace, beating their wings slowly. They occasionally fly close to the water’s surface and dive to spear prey.
Male and female herons look very similar. For half the year, they are solitary, each with its own feeding territory in the Bay’s wetlands. But starting in January or February, they gather in colonies to breed and nest. Males arrive first at breeding colonies, adorned with special plumes that grow during mating season. Females arrive a few days later, also with their mating plumes on display, and males begin courtship postures and behaviors. The herons pair up, forming a bond that will last until their chicks have grown, and start building a new nest or adding to a nest left over from previous years. Made from sticks, the nests are two to four feet wide, usually in tall trees.
Pairs of herons chatter with each other by rapidly snapping their beaks. Females lay three to five pale blue eggs, slightly larger than hen’s eggs. Males and females take turns sitting on the eggs, which hatch in April. The parents also take turns feeding the chicks, one finding food while the other stays at the nest. By June, great blue heron chicks test their wings in flight. By August, the chicks have grown to full size and left the nest, and are catching their own food in their own solitary territory in the Bay’s wetlands.
Adult herons have few predators, but raccoons and feral cats prey on heron eggs and chicks. If humans intrude into heron nesting areas, chicks may not survive and the herons may not return to the area in following years. You can help great blue herons thrive in the Bay Area by keeping away from nesting areas. Some adult herons will casually stroll close to humans. For others, a human coming close can be stressful. When in doubt, keep your distance.
Great blue herons need wetlands for habitat. The more Bay wetlands can be preserved and restored, the more we will see of these powerful and elegant birds. The great blue heron also needs clean, healthy Bay water to survive. Like sea lions and harbor seals, herons are among the top predators in the Bay. If the fish herons eat have been swimming and feeding amid toxic pollution, these birds accumulate a heavy load of harmful contaminants in their bodies.
Baykeeper is working to stop pollution that runs off into the Bay during storms from industrial facilities and city streets, to protect great blue herons and all the wildlife of San Francisco Bay.