Meet the Great Blue Heron
Meet the Great Blue Heron
That tall, greyish bird with a thick, yellow bill standing motionless in the shallow water along the Alameda shore is most likely fishing. These birds are great blue herons (yes, blue, even though they may look grey), who use their long bills to catch fish. Then they toss the fish into the air, turning it head-first to swallow whole.
They may stand still for a long time before moving swiftly to nab their prey. In addition to fish, they eat frogs, snakes, mice and other small mammals, so they may also be found in fields.
Great blue herons are large, about 4.5 feet tall and 4 to 6 pounds when fully grown, with a wingspan of 65 to 80 inches, or about 6 feet. Adults have a black stripe over the eye, which extends into a black plume, and their necks often form an “S” curve. Along Florida’s southern coast a white subspecies may be found, but those in Alameda are bluish-grey.
The long, black head plume and white plumes on its neck when breeding were once sought for women’s hats and soldiers’ parade helmets, a practice that led to the creation of many local groups opposing such hunting. Many of those groups are now local Audubon chapters.
Great blue herons may be seen year-round in Alameda, though the individuals nesting here may have spent the winter further south, and those wintering here may have nested further north.
Look for nesting great blue herons at DePave Park on the west side of Seaplane Lagoon at Alameda Point. The trees behind the fence on the west side of the paved area are favored nesting habitat and house active nests again this year.
A red-tailed hawk also favors these trees this year; it will be interesting to observe what happens. The great blue herons’ large nests are built of sticks and leaves, and may also include odd pieces of cloth, string and plastic, including fishing line. The chicks may get tangled in the line, so it’s important to retrieve snagged fishing line and dispose of it properly.
These herons are colony nesters, so there are usually several active nests in each nesting tree. Some rookeries contain hundreds of nests spread over many trees. While the nests are reused for many years, the same birds may not use a nest from year to year, and they may not nest with the same mate each year. The acid in the birds’ droppings eventually kills the trees, so the nesting trees seen from the park are dying under the birds.
Great blue herons usually lay between two and six pale, blue eggs. During the day, both parents will incubate the eggs (sit on them to keep them warm); the female usually takes the night shift.
The chicks hatch in 26 to 30 days; both parents feed and brood them (sit over them to keep them warm and safe). The chicks can fly at seven to eight weeks after hatching but stay with their parents for another two to three weeks. The young birds will start to nest in their third year.
Hawks, ravens, crows and raccoons can steal great blue heron eggs or chicks. Intrusions by humans may cause adults to leave the nest temporarily, leaving eggs or chicks vulnerable to predators. Frequent human intrusions can cause adult birds to abandon a nest altogether.
Adult herons have few predators, but they are vulnerable to entanglement with fishing lines and other plastic trash. Toxins in the water or fish can accumulate in a heron’s body, eventually causing its death. A great blue heron that avoids these and other risks can live for 30 years.
Proper disposal of household and industrial chemicals will help keep the herons and people that rely on San Francisco Bay fisheries healthy.
For more information on Golden Gate Audubon Society and its Friends of the Alameda Wildlife Reserve conservation committee, go to www.goldengateaudubon.org.