Green herons are seasonally monogamous. Courtship displays are stereotyped. They begin with Flying Around displays resembling natural flight, but oriented to breeding sites with skow calls. From here, courtship becomes aggressive. Pursuit Flight, Circle Flight and Forward displays are used, where a rasping 'raah-raah' call exposes the red mouth-lining. Crooked-Neck Flight displays are more aggressive, where the neck is partially flexed, legs are dangled, and wingbeats are audible. Much like the Crooked-Neck Display, the Flap Flight Display shows the greatest intensity of flight displays. Here, the male lurches through the air with exaggerated flapping producing a whoom-whoom-whoom sound in a crooked-neck posture with crest, neck, and scapular feathers erect and often giving a roo-roo call before landing.
Nonaerial displays are interspersed with display flights. In the Snap Display, the male perches, then points body, head and neck down until bill tip is at or below the level of his feet and then snaps his mandibles together, producing a click while also erecting his feathers. The Stretch Display involves the male pointing his bill straight up, stretching his neck, and then bending it backwards until the head almost touches its back with interscapular plumes erect and fanned. In this posture, he sways his neck and head from side to side with crest, breast, and flank feathers sleeked back, eyes bulging, and iris possibly turning from yellow to deep orange while emitting an aaroo-aaroo sound.
Males perform this Stretch Display before a female is allowed to enter the eventual nest area. The female then performs a less intense Stretch silently after the male, which confirms the pair-bond. At this time, the male stops Flight and Snap displays. The pair then engages in mutual bill-snapping and feather nibbling, though those behaviors are reduced soon thereafter. Copulation occurs on the nest platform during the nest-building stage. It lasts about ten seconds with several hours between copulations. (Davis and Kushlan, 1994; Hancock and Kushlan, 1984)
Mating System: monogamous
After the last egg is laid, copulations cease and incubation persists for 19-21 days. A normal clutch is 2 to 4 eggs, laid in 2-day intervals. Fledging occurs when chicks are 16 to 17 days old, and independence is gained between 30 and 35 days.
Nesting takes place in forest and swamp patches, over water or in plants near water. Nesting pairs normally nest alone, but loose aggregations of mated pairs can form. Nest building is a cooperative effort, with the male participating more in protection versus actual construction. Nest placement can be from ground level to 20 meters, depending on plant height and thickness; branches in trees are favored. There is no attempt at nest sanitation, though chicks void over the edge of the nest once they're able to walk.
Breeding interval: Green herons breed once yearly.
Breeding season: The time of breeding varies considerably geographically, generally breeding begins anytime from March through July.
Average eggs per season: 2-4.
Range time to hatching: 19 to 21 days.
Range time to independence: 30 to 35 days.
Average age at sexual or reproductive maturity (female): 1 years.
Average age at sexual or reproductive maturity (male): 1 years.
Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); fertilization (Internal )
Average eggs per season: 4.
Both adults feed and brood chicks, though at less frequent intervals as the chicks become more independent.
Parental Investment: altricial ; male parental care ; female parental care
- Davis, W., J. Kushlan. 1994. The Green Heron. The Birds of North America.
- Hancock, J. 1999. Herons and Egrets of the World. London, UK: Academic Press.
- Hancock, J., J. Kushlan. 1984. The Herons Handbook. New York City, NY: Harper and Row Publishers.