A chicken-like, ground-dwelling bird with a long neck, long legs and a hump-backed profile. Ashy gray inner wings and rump contrast strongly with their black body, and form a prominent hind-wing patch that is bordered on back by a chestnut-brown stripe. Largely terrestrial and quite gregarious, they spend most of their day in noisy flocks roaming the forest understory in search of food.
Overall quite similar to the other two species of trumpeters, the Pale-winged Trumpeter (Psophia leucoptera) and the Dark-winged Trumpeter (Psophia viridis), but are easily distinguished by the colors of their wings and rump. The Pale-winged Trumpeter is distinguished by its white or ochre hind wing patch, while the Dark-winged Trumpeter has dark wings and an overall greenish sheen. There also is little or no range overlap between any of these species.
The neck, usually held in an S-curve, appears quite slender and the head seems quite small, as both are covered with short, dense, and velvety looking feathers. The eyes are large and dark brown and the beak is reminiscent of that of a gallinaceous bird, being sharp, stout, and slightly decurved at the tip.
The body appears large and hump-backed, as the broad wings are held slightly open and cover the short tail and much of the body. The Gray-winged Trumpeter, like all trumpeters, is predominantly black, but the rump, lower back, and inner wings (secondaries, tertials, and their coverts) are light ashy grey, and bordered on the middle back by a chestnut-brown stripe. All together this gives the appearance of a large oval-shaped "hind-wing patch" that covers much of the back end of the bird. This patch appears more uniform due to the presence of hair-like filaments, originating in the lower parts of the inner wing coverts, which soften the constrast between the different feather tracts that comprise the patch. The lower throat has purplish-blue to greenish iridescence, which can be seen up close in the following video. Trumpeter plumage does not vary between the sexes, but males tend to be slightly larger (See Measurements).
The following detailed dscription is based on Blake (1977):
Sexes similar. General color black. The lower back and the scapulars are more less ferruginous. The secondaries and tertials are ash gray. The feathers of the lower foreneck and the chest are tipped with metallic green and violet or bronzy purple.
Little information. In the closely related Pale-winged Trumpeter (Psophia leucoptera), feathers in the adult plumage are replaced gradually over the course of a year; presumably the same is true for the Gray-winged Trumpeter (Sherman 1996).
Data from Blake (1977, Haverschmidt and Mees 1994):
Iris: dark brown.
Bill: yellowish green.
Tarsi and toes: Greenish olive.
Total length 45-52 cm (Blake 1977), 46-52 cm (Ridgely and Greenfield 2001).
Blake (1977) provided measurements of wing length, exposed culmen, and tarsus for 35 birds, representing both races and sexes. All measurements are in millimeters.
For males (n=9) of the nominate subspecies, crepitans:
Wing (flat): mean 280.1 mm (range 270-286 mm); exposed culmen: mean 33.6 mm (range 31-35 mm); tarsus: mean 128.3 mm (range 121-137 mm)
For females (n=9) of the nominate subspecies, crepitans:
Wing (flat): mean 278.6 mm (range 267-293 mm); exposed culmen: mean 32 mm (30-34 mm); tarsus: mean 122.3 mm (range 121-125 mm)
For males (n=7) of the subspecies napensis:
Wing (flat): mean 291.9 mm (range 281-311 mm); exposed culmen: mean 33.6 mm (range 31-35 mm); tarsus: mean 129.7 mm (range 118-138 mm)
For females (n=10) of the subspcies napensis:
Wing (flat): mean 289.6 mm (range 273-302 mm); exposed culmen: mean 33.1 mm (range 30-36 mm); tarsus: mean 126 mm (range 110-136 mm)
Mass: Data from Haverschmidt and Mees (1994): 2 males, 820, 1019 g; females (n=6), mean 1060 g (range 790-1500 g)