A typical Progne martin: a large, sexually dimorphic swallow, with a slightly forked tail. The male is mostly blue-black, with a broad white area on the lower breast and undertail coverts; the sides are blue-black. The female has a similar pattern, but is duller, with a gray-brown throat and upper breast, and sides to head. See Similar Species.
The Sinaloa Martin very closely resembles the Caribbean Martin (Progne dominicensis), and it has often been considered conspecific with that bird (see Systematics). The breeding distribution of Caribbean and Sinaloa martins do not overlap. Presumably they also winter in separate areas, but geographic overlap during the nonbreeding season is a possibility. Sinaloa Martin would be difficult to distinguish from Caribbean Martin in the field, and perhaps even in the hand, on the basis of current information. The male is described as "exactly similar to" Caribbean Martin in plumage (Ridgway 1904), but averages slightly smaller. For example, Ridgway (1904) gave the following data on wing length of males: Sinaloa is 136.7 mm (mean; range 136-138 mm) and of Caribbean is 143.5 mm (range 134-149 mm) . Zimmer (1955) Phillips (1986) also report that there is a subtle difference in the pattern of the underparts, in that the white abdomen of Sinaloa is broader, in contrast to more extensively dark flanks in Caribbean.
Females of the Sinaloa and Caribbean martins also are very similar to one another, and perhaps not distinguishable except by average differences in size. They are also similar to the Gray-breasted Martin (Progne chalybea) and to female Purple Martin (Progne subis). Female Sinaloa Martin has a darker throat and upper breast than Gray-breasted or female Purple martin, with more contrast between the dark breast and white belly, and the belly and undertail coverts are pure white; the underparts of Gray-breasted and female Purple martins are finely streaked dusky. Female Purple Martin further differs from Sinaloa by the paler (gray) forecrown and nuchal collar, and by its larger size (Davis 1972, Peterson and Chalif 1973, Howell and Webb 1995).
A large, dark swallow with a forked tail. The following description is based on Ridgway (1904) and Turner (2004):
Male: Mostly glossy steel-blue. The lower breast, belly, and undertail coverts are pure white, except for some dark spots or a dark band across the undertail coverts. Underwing coverts and axillars are gray-brown. Wings and tail are black with a bluish gloss.
Female has generally duller coloration. Upperparts duller blue, sometimes mottled with gray-brown. The sides of the face, and the throat, breast and flanks are dusky brown; the center of the throat is paler than the sides of the throat. The middle of the throat is pale compared to its darker breast. The lower breast, belly, and undertail coverts are pure white, and are sharply separated from the darker throat and upper breast.
The first year male is similar to the adult female, but has blue feathers on its upperparts and some blue feathers on its breast as well (Howell and Webb 1995).
Juvenile undescribed (Howell and Webb 1995, Turner 2004).
Very little data.
Total length 17-18 cm (Turner 2004), 17-18.5 cm (Howell and Webb 1995).
Linear measurements of three males (Ridgway 1904):
Wing length: mean 136.7 mm (range 136-138 mm)
Tail length: mean 69.5 mm (range 67-72 mm)
Depth of tail fork: mean 17.5 mm (range 16.5-19.5 mm)
Bill (exposed culmen): mean 10.1 mm (range 10-10.5 mm)
Tarsus: mean 13.2 mm (12.5-13.5 mm)
Mass: sample of 3 (combined male and female), mean 42.6 g (range 42-43.7 g; Dunning 2008)