Brown Jays are large and dull-colored relative to most New World jays. This species easily is identified by size, its overall dark brown plumage, pale white or light brown belly andvent, long rounded tail, and black bill. Two morphs, plain-tailed (or brown-tailed) and white-tipped, are distinguished by presence or absence of white tips on the retrices. The bare part colors vary based on age. The bill, tarsi, and eyering are completely black in adults but are yellow or mottled yellow and black in subadults. Males and females are identical in plumage but females are smaller than males.
Few species occupying the same range are similar in appearance to Brown Jay. Female or juvenile Great-tailed Grackles (Quiscalus mexicanus) may be confused for Brown Jays at a distance, however the white belly and vent of the Brown Jay makes it easily distinguishable. In flight, Brown Jays may be confused with the even larger Plain Chachalaca (Ortalis vetula), which has a longer neck and smaller head.
A large, magpie-sized jay with a dark brown uppertail, rump, back, and scapulars. Plumage gradually changes into dark brown or black at the head and neck. The upperwing feathers are olive gray and often have an indistinct bluish sheen (Selander 1959). Dark, sooty brown extends down the throat and breast. The belly and vent are pale buffish brown or pale white; however, melanistic individuals are purely sooty brown (Selander 1959). Short bristle feathers form a small frontal crest. Birds have an indistinct brown malar stripe as a result of different feather structure (dos Anjos 2009). The tail is highly graduated and retrices are uniformly brown in plain-tailed morph, while in white-tipped morphs central retrices have white on edges. Sexes are indistinguishable by plumage, however females are signficantly smaller (dos Anjos 2009). Juveniles are paler than adults and generally have gray irides.
A few months after fall molting, dark brown coloration of feathers fades into paler brown. Immediately prior to molting, feathers will often appear grayish brown (Selander 1959).
Bill, tarsi, toes, and eyering are yellow in juveniles and mostly black in adults. The age at which soft part colors turn completely black is highly variable, taking 4 or more years (Lawton and Lawton 1985). Soft part color can even be used to identify individual birds (Skutch 1960). Adults of both sexes and individuals in juvenile plumage possess a bare furcular pouch that inflates with air to create a hiccup sound. When deflated, the pouch occupies the interclavicular space near the sternum and is covered by breast and throat feathers (Sutton and Gilbert 1942). The pouch becomes visible when inflated and measures roughly 2 cm in diameter. The pouch is made of tough, "powdery" skin and contains sparsely distributed down feathers (Sutton and Gilbert 1942).
Total length: 38-44 cm
Linear measurements (from Ridgway 1904; nominate morio):
male (n = 7)
wing length, mean 208.5 mm (range 201.9-215.9 mm)
tail length, mean 218.2 mm (range 210.3-226.1 mm)
bill length (bill from nostril), mean 28.4 mm (range 26.2-31.7 mm)
tarsus length, mean 50 mm (range 47.5-52.1 mm)
female (n = 4)
wing length, mean 202 mm (range 198-206 mm)
tail length, mean 209 mm (range 200.5-214.5 mm)
bill length (bill from nostril), mean 26.5 mm (range 25.5-28 mm)
tarsus length, mean 50.5 mm (range 49.5-51.5 mm)
Mass: male, mean 209.75 ± 3.90 g (range 193.6-224.3 g, n = 8; Paynter 1955); female, mean 195.08 ± 3.18 g (range 173.2-203.2 g, n = 5; Paynter 1955)