Green Ibises spend the day silently foraging in concentrated areas of wet mud and shallow water, but roost in the understory of trees three to five m above ground during the night (Ogden and Thomas 1985). They spend less time at the roost than other species, entering after sunset and leaving before sunrise (Ogden and Thomas 1985). They are also more wary than similar species (Thomas and Ogden 1985). When disturbed, it turns its head jerkily while nodding and making a clucking sound, then flies to nearby trees where it continues to call unseen (Hancock et al. 1992).
A pair was observed harassing Sunbittens (Eurypyga helias) in their nest, attempting to and succeeding in entering the nest before being chased away (Thomas and Strahl 1990). This did not prevent a Sunbittern pair from building a nest in the same spot the next year (Thomas and Strahl 1990).
Green Ibis pairs seem to use distinct feeding and roosting sites for much of the year and establish territories by calling (Hancock et al. 1992). During the nesting season, solitary birds or pairs are observed (Hancock et al. 1992). The groups of two to six observed during other parts of the year are most likely family groups (Hancock et al. 1992).
It appears as if the color of bare body parts becomes enhanced during the breeding season, with legs shifting from pea-green to metallic green, the throat skin becoming violet, and when the gular pouch is extended during courtship, a bright blue cheek line becomes apparent (Hancock et al. 1992). The courtship display occurs at the top of a tree; one bird performs a Head Shaking display, which the other mimics, then the two duet with a soft deep "Brrr" call; necks are held near vertical with head feathers elevated (Hancock et al. 1992). When the duet ends, the head shaking resumes and the pair bump bills (Hancock et al. 1992). The gular pouch may be flared during this display, revealing a bright blue cheek line (Hancock et al. 1992). Stick Sharing and allopreening may end the courtship ritual, but these behaviors are less common in this species of ibis (Hancock et al. 1992). To initiate copulation, the male sweeps his bill back and forth in front of the female (Hancock et al. 1992). During copulation, the male tries to grab the female's bill and may hold on throughout (Hancock et al. 1992).
Social and interspecific behavior
Green Ibises are not very social, foraging alone and roosting in small groups (Ogden and Thomas 1985). They forage at the edge of mixed-species flocks, though their closest foraging neighbor is usually a conspecific (Frederick and Bildstein 1992).
Capuchin monkeys (Cebus) have been observed eating young in the nest (Hancock et al. 1992). The parents and young are both very secretive at the nest, with parents refraining from any calls except quiet gurgle and young using a light buzzing call to beg and crouching down in the nest when approached, suggesting high predation pressures during nesting (Hancock et al. 1992).