Trumpeters are highly social birds, and spend their lives in cohesive flocks. The details of the behavior of Gray-winged Trumpeters are little studied, but probably are similar to the behaviors of the Pale-winged Trumpeter (Psophia leucoptera), which has been studied in southern Peru. Trumpeter flocks have a defined dominance hierarchy and consist of birds of all ages and sexes. Dominance is recognized by means of a highly ritualized "Wing-spread" display, during which subordinate birds face a dominant bird, lower their heads, extend their wings horizontally, and give a call similar to the high-pitched twittering call of trumpeter chicks. This display is given by birds of all ages and is most commonly given just after dawn, a period during which birds fly down from their roost and reestablish their social rank for a few minutes. The Wing-spread display exposes the secondaries, which are darker on juveniles, and makes the bird vulnerable to attack, and thus a low-ranking bird seems to show a higher ranking bird that it is younger and subordinate. Dominant birds often respond to the Wing-spread display with a "Wing-flick," in which the folded wings are swiftly lifted up and forward and then brought down again.
In Pale-winged Trumpeters, individuals under three months old preform the wing-spread to all individuals, but older birds generally display to individuals of the same sex, maintaining a within-sex dominance hierarchy.
Most of the day is spent roaming the forest understory in search of fruit and arthropods and patrolling the flock's territory. Should a flock detect a trespassing group of trumpeters, the flock will run very rapidly towards them. Sometimes the trespassers are chased off, but more likely the trespassers are caught and a fight ensues. While driving out trespassers, birds run towards birds of the same sex with their head down and their wings arched upwards and the primaries and secondaries drooping towards the ground, and proceed to alternately peck and then flap up and kick the intruding birds, ever after they have fallen down, until the intruder flees or fights back. This continues until the intruders are chased back into their territory. Males are more likes to fight, while females and juveniles often stand back and give the loud territorial trumpeting call. After the intruders are chased onto their territory, Pale-winged Trumpeter males in both groups will then make submissive Wing-spread and dominant Wing-flick displays and will even offer food to males of the other group. It is during this time that subordinate adult males will often switch between groups, but will return to his home group after a few weeks if he does not succeed in achieving a higher rank. It is thought that males do this to increase their chance of breeding, and as a result there is genetic mixing between groups.
Allopreening and Social Feeding
Pale-winged Trumpeters spend more time loafing in response to increases in their food supply, and forage more diligently when food is scarce. When food is abundant, groups move slowly, and stop often to preen and bathe and sun. Adult Pale-winged Trumpeters frequently solicit preening from each other by bowing their heads towards other adults, who then rapidly open and close their beak as they run it through the feathers of the head and neck of the receiving bird, removing parasites and dead skin. Juveniles will solicit preening from adults or other juveniles. It does not seem that rank explains the amount a bird solicits or receives allopreening.
Trumpeters will often use food socially, especially when it is abundant. Pale-winged Trumpeters have been observed picking up a piece of fruit or an arthropod and hold its head high and arch its wings and walk around repeating a single, medium-pitched call note. Adults of the same sex or juveniles will then lower their head and give the submissive twittering and the food-begging call. The feeding bird will hold the food above the begging birds for a few seconds to a few minutes before it is given to one of the begging birds. Instead of swallowing it, occasionally the recipient of the food will pass it back and forth with the food donor several times until one of them swallows it. Dominant birds will even beg for food from lower-ranked individuals, but if the lower-ranked bird does not give the food within a few seconds the dominant bird will snatch it away.
Play, both solitary and social, is common among trumpeters, and much of it seems to mimic territorial squabbles. Birds will peck and kick at leaves and twigs, jump up in the air and flap, and run with the head lowered and the wings arched. When more than one individual plays they often chase each other between pecking at objects and will even face off and peck at each other without hitting, after which the birds split up and chase other birds. Birds tend to play for only a few minutes at a time.
When night falls trumpeters fly 8-15 m up to roost in trees, and tend to spread out into different parts of the same tree or different nearby trees. Trumpeters roost in different areas each night.