Critter

Great Blue Heron

David Rosen, Wildside Photography

Common name: Great Blue Heron

Scientific name: Ardea herodias
Phylum: Chordata
Class: Aves
Order: Ciconiiformes
Family: Ardeidae
Habitat: vernal pools, rivers and lakes
Size: 1.0 to 1.4 meters tall

Description: The Great Blue Heron is a wading bird. It has a blue-gray back, black patches on its sides and a gray and white-striped belly. The cheeks, throat, and top of the head are white. It has a black stripe over its eye and a long, black feather decorating the back of its head. Its bill is yellow and its legs are greenish-brown.

Fun facts: The Great Blue Heron makes a sound like a loud, rusty squawk. The noise that comes from a colony of nesting Great Blue Herons is very loud. What do you think is the advantage for the herons to nest in large colonies?

Life cycle: Great Blue Herons make nests and raise their young in areas called heronries. A heronry is a group of trees where about 20-50 mating pairs build their nests. These nests may be reused year after year, if they are not destroyed by winter storms.

In March, the males arrive at the heronry and select a nest. Each male then performs his courtship display and the females choose their mates. Males and females commonly mate for life. After repairing the nest with reeds, grass and moss, the female lays 3 to 5 pale blue eggs, about 5 cm in diameter. The male and female take turns sitting on the eggs for about 28 days.

When the hatchlings emerge, both parents feed them a diet of regurgitated (thrown up) food. Later, whole dead prey are dropped into the nest. A few weeks after hatching, the young begin to test their wings and fly short distances. The young grow quickly and are adult size by 42 days old. After 60 days, they leave the nest.

Ecology: Great Blue Herons wade in shallow water hunting for food. In vernal pool grasslands, the Great Blue Heron eats many things including Clam Shrimp, Tadpole Shrimp, California Tiger Salamanders, Dragonfly and Damselfly larvae, snakes, Pocket Gophers, and the tadpoles and adults of the Western Toad, Pacific Chorus Frog and Western Spadefoot. Due to its large size, an adult Great Blue Heron has few predators. However, its young are less able to defend themselves. They are preyed upon by Red-tailed Hawks, eagles, ravens and raccoons.

Conservation: The California Department of Fish and Game has discovered that the heron population is getting smaller. The Great Blue Heron is a “species of concern”, meaning that it could become endangered if this trend continues.

The loss of herons is mostly due to habitat disturbance. People are constructing buildings in places near heronries. Herons are very sensitive to human presence around their nests. They will abandon eggs and young if they are disturbed. Another problem is the pollution of the marshes, lakes, and rivers where herons feed. If these water bodies are polluted, it can kill the Great Blue Heron’s prey. If the herons do not get enough to eat, they cannot survive.

Investigate: If you visit vernal pool grasslands when the pools are full of water, you are likely to see a Great Blue Heron foraging (hunting) near the pools. Herons still come to the vernal pool grasslands after the water has evaporated in the spring when the pools are full of flowers. What critters do you think they are eating?

Commands