Life History
Great blue herons breed across the United States and southern Canada, and more than half of the Atlantic coast's breeding population nest in Chesapeake Bay--predominantly in wetlands. Although many herons migrate through the Bay region, some great blues remain in the Bay area year-round. These waterbirds use a variety of different feeding methods to procure their primary diet. Great blue herons are one of the top predators of the Bay food chain.
Physical characteristic
Great blue herons are large birds (6-8 lbs.) with long legs. They have long necks and stand up to four feet tall. Their heads are white with a dark wide stripe and their bodies are blue-gray.
Habitat
Great blue herons live around both fresh and salt water. They nest close to each other in colonies called rookeries. They can be found along the edges of streams, ponds, lakes, rivers and bays. They breed in the eastern portion of the state but can be found state wide other times of the year.
Food
Wading in shallow water, great blue herons hunt for fish, frogs, crayfish and snakes. Their long pointed bill also helps them catch insects, mice and other small animals. Other kinds of Herons in Maryland: Eight other herons live in Maryland. These are the little blue heron, tricolored heron, green heron, black crowned night heron, and the yellow crowned night heron. The cattle egret, snowy egret, and great egret are white herons which live here.
Other Characteristics
Great blue herons have a seven foot wingspan and can fly 20-30 mph. Although some will spend the winter in Maryland, most will migrate to states further south.
In flight, the Great Blue Heron's large size, broad wings, and bent neck make it almost unmistakable. This bird gives the general impression of being tall and thin: its wings, neck, bill, and legs are long. The long limbs dictate the heron’s movements: it flies with deep, slow wing beats, and on land, or in the water, it walks erect with long strides. In flight, the neck is doubled back, the head resting against the shoulders, and the long legs held straight behind The top of the adult’s head is white with a black stripe on each side extending from the yellow eyes to slender black plumes at the back of the head. Its back is greyish blue, and its breast is white streaked with black.
Life Cycle
Female herons lay 3 to 5 eggs on average with smaller clutches in the south and larger ones in the north. Eggs are laid in March or April at the northern edge of the range in British Columbia and Alberta and in January and February in northern California. In Florida, eggs are laid at all times of the year with most of the breeding occurring in the autumn and late winter. Eggs are pale blue in colour and measure about 50 to 76 millimetres in length and 29 to 51 millimetres in breadth. A freshly laid egg weighs about 71 grams. Both members of the pair incubate the eggs for about 26 or 27 days. Incubation begins shortly after the first egg is laid so that the clutch hatches asynchronously. Each incubation bout lasts several hours interspersed with bouts of egg turning every few hours. A hatched chick weighs about 50 grams.
Herons can live for 18 years in the wild but most adults probably live for about 10 years. Young herons have a much high mortality rate than adults. About half the eggs laid become fledged chicks. There are few data on how many juveniles survive their first year but it is likely about 20%.