Great Blue Heron Behaviour

Coastal dwelling herons eat mostly small fish that they catch while wading in shallow water. The fish are snatched from the water and only large prey is speared. The rapid uncoiled neck and long pointed bill act like a spring loaded tweezers. Herons will eat any animal they can swallow including fish, small muskrats, rats, meadow voles, birds, reptiles, amphibians and insects. In the Northwest, herons wade in water, and balance on floating seaweed, logs and wharves to hunt fish. They will also move into streams, ditches and ponds in search of fish and amphibians, and into fields for small mammals.

Flight Patterns of the Great Blue Heron

Herons fly with slow but powerful wing beats often in straight and steady flight. The neck is folded over the shoulders most of the time. Herons can take advantage of thermals that lift them high in the sky to glide or slowly fly to distant feeding locations.  

Aggressive, Defensive & Territorial Displays of the Great Blue Heron

Territorial display sequence

Herons will attempt to defend several hundred meters of shore along river edges, ponds and other wetland areas against other herons. The most noticeable way they defend these sites is by chasing off intruders. Herons on adjacent territories display to one another by extending the wings away from the body, arching the neck, pointing the bill a few degrees above horizontals and erecting the feathers.

Courtship & Breeding Behaviour of the Great Blue Heron

Unpaired males perform the stretch display that begins by raising the bill until it is held vertical, extending the neck and erecting the feather plumes while uttering a ‘goooo-gooo’ sound. The display shows off the plumes and coloured soft skin parts around the eye and bill to females seeking mates. The snap display begins with the erection of neck and head feathers. The heron moves its head forward and downward to culminate with a snapping of the bill. Both the snap and stretch displays are confined to the nest or nearby branches. Herons also display in the air by slow glides or laboured flaps of the wings with the neck outstretched. Throughout the nesting season herons will alight at the nest often uttering a loud croak and erection of the feathers. This display is likely a greeting between mated pairs.

Nesting Habits of the Great Blue Heron

Herons display to show off their plumages to their mates during courtship, to signal arrival at the nest, and to defend favourite foraging places. The plumes of feathers are thought to be signals of their quality at providers. Elsie Krebs and her coworkers showed in a paper published in the journal ‘Behaviour’ in 2004 that egrets tended to select mates with similar length plumes and females tended to mate with males other than their own that had the same or longer plumes. Herons also develop brightly coloured soft parts around the eye and bill. The soft parts can be aquamarine or yellow. The bill colour turns bright orange yellow when pairs are mating – at other times of the year the bill is washed out yellow and grey green in colour. Great Blue Herons exhibit many displays at or near the nest. Doug Mock described several of the courtship displays in a paper he penned in 1976 in the journal ‘Wilson Bulletin’. 

Nests are built from twigs place in trees carried there by the male and placed by the female. Eggs are laid as early as February in the south and April in the north. A Great Blue Heron lays an egg about the size of a chicken’s egg. The egg weighs about 70 grams when it is laid and it is greenish blue in colour. Eggs measure 50.7 to 76.5 mm in length and 29.0 to 50.5 mm in breadth. A very small egg is occasionally found in a clutch. Females lay an egg about every 2 to 3 days until the clutch is complete. In Florida, a clutch is 1 or 2 eggs while in Alberta a clutch is about 5 eggs.

Summary of breeding data for herons across North America (adapted from Butler 1997)

Females begin to incubate before the last egg is laid. Incubation requires about 27 days – the time is divided between the male and female with each sitting for many hours. They briefly stand to stretch their wings and legs, defecate, and to turn the eggs. Mates will be off feeding or perched in the trees asleep, watching or tending their feathers. The colony is very quiet at this time as the parents attentively care for the eggs deep inside the nest.

Eggs hatch over several days. The reason why herons hatch eggs asynchronously is not fully understood. Some researchers believe that it adjusts the size of the brood to the food supply but the evidence is not strong. It is more likely related to a premium on survival for early nest departure of young herons. Early departing herons probably have more time to learn how to catch prey when food is still plentiful.

Upon hatching the young chicks begin to call with weak peeping sounds. They sport white top-knots on their heads and grey feather tracts along their pink skinned bodies. A newly hatched chick weighs in at about 53 grams. They have tiny beady blue eyes. At a week old, they begin to preen their feathers and by two weeks they are capable of staggering to their feet.  By four weeks of age, a heron chick is well feathered and it can flap its wings. The parents can leave the chicks for long periods at this age becsue their feathering allows them to remain warm without the body warmth of the parent. Chicks make short hops to branches at about seven weeks of age and recognize their parents. By 8 weeks, some of the young herons will leave the nest for their inaugural flight. They now weigh in at 2100 to 2400 grams. About two thirds of the food brought by the parents is used by chicks to remain warm and move about the nest. One third goes into growth.

A young heron is fully fledged but its foraging skills are very poor. Learning to find and catch fish takes days or weeks for a young heron to master and several years to become proficient. Many young herons will die at this time.

Vocalizations and Calls of the Great Blue Heron

Herons are largely silent birds. When they become alarmed, herons utter a loud call sounding like ‘wronk’ repeated several times. They also have a nesting repertoire that includes cooing, and hoarse ‘fraunk’ sounds.