The three trumpeter species are some of a very small number of polyandrous cooperative breeding birds. Since their flocks have a strict pecking order, the rank of an individual bird determines if it will be one of the few that breed, and all members of a flock assist with raising the offspring. Only eight other birds species are known to have this mating system where several males copulate with a single female and help to raise the young; these include the Tasmanian Native-hen (Gallinula mortierii), the Galapagos Hawk (Buteo galapagoensis), the Dunnock (Prunella modularis), and the Striped-backed Wren (Campylorhynchus nuchalis).
Much of the work done on trumpeter breeding has been done on the Pale-winged Trumpeter (Psophia leucoptera), but as the two species are very closely related much of the information is likely quite similar.
Mating and Courtship
It seems that trumpeters time their breeding so that the eggs hatch at the start of the rainy season, the time when insects and fruits become most abundant.
Nesting site selection
In Pale-winged Trumpeters, the dominant pair begins examining nest sites two and a half months before the clutch is laid. Most nest site are tree cavities that were originally excavated by other species such as parrots, thus providing some shelter from the rain. A roof does not seem to be needed: twice the Pale-winged Trumpeter has been recorded nesting in the crack where a tree trunk splits into two (Sherman 1995a), and Gray-winged Trumpeters will nest in a roofless cavity atop a snag of the tree Vouacapoua vouacapoua 13.5 meters up (de Mercey and Théry 1999). No nest is built within this wooden cavity.
Laying and Incubation
Trumpeters lay between two and four eggs, most commonly three. Eggs are all white, and are 56-61 x 46-50 mm in dimension. In one study in French Guiana between 1993-1997, all eggs (n=7) were laid in February or March (de Mercey and Théry 1999). Breeding records in the Guyana shield range from December to May: chicks in March in French Guiana (Tostain et al. 1992) and in February and April in Guyana (Haverschmidt 1985), an egg laying in December and May for a captive pair in Suriname (Haverschmidt 1963), and an adult male in breeding condition was captured in March near the upper Orinoco, Venezuela (Hilty and Brown, 1986). The Gray-winged Trumpeter has bred in captivity in two North American zoos, and it has been found out that the eggs are incubated for 28 days before hatching (Horning et al. 1988, Male 1989).
Trumpeter chicks are nidifugous and precocial and are born covered with a thick layer of down. The face and wings are a russet color, while the crown and back are dark gray. The underparts are cream-colored, and a black bib covers the throat and upper breast. A russet strip runs over the top of the head from the top base of the mandible to the back of the neck, and other reddish stripes run lengthwise down the back.
Chicks jump out of their nest box before they can fly, apparently to little ill effect, and begin begging for food almost immediately. The duty of chick feeding is shared by all members of a group, though some individuals feed the chicks more than others. Sherman found that in Pale-winged Trumpeters non-breeding females and the dominant male contributed somewhat less to feeding the chicks, but such information is not known for Gray-winged Trumpeters.
Chicks are reliant on older members of their flock for protection and feeding. By ten days they flight feathers begin to come in, and by six weeks they can fly short distances and look like small adults. For the first three weeks they rely on other birds for feeding, by week four they contribute 25% of their own food intake, and by three months they are self-reliant but continue to beg for some time.