Streak-backed Oriole Icterus pustulatus Scientific name definitions

The Streak-backed Oriole is a widespread oriole found from N Mexico south through Central America, although largely restricted to the Pacific Slope. It has bred on occasion in Arizona, and vagrants have made it well to the north, suggesting that there are some regular migratory movements in the northern populations at least. Perhaps the most unusual and intriguing aspect of this oriole’s biology is that in the north of the range the males are superbly bright, and the females reasonably dull. However as one proceeds southwards, the females become more and more male like until at the south end of the distribution the two sexes are nearly alike! Also male like females are more apt to help in territorial defense. The ecological difference appears to be that in the south they are year-round territorial, requiring a greater effort by the female to help in territorial matters than in the north where they are territorial only during the breeding season and also partly migratory. It is also interesting that monomorphic plumage in all orioles tends to occur when the female looks bright and male like, not as in many other birds where monomorphic species are both dull colored. The northern population of the Streak-backed Oriole has males which are very salmon to reddish orange on the head, at one point they were given the name Flame-headed Oriole. This very reddish coloration is not common in orioles, nor is the streaked back of this species; other orioles have either black backs or orange to yellow backs.

19–21 cm; male average 43·1 g, female average 34·6 g; sexes combined 31·8–41·6 g (microstictus), 29–39·4 g (graysonii), male average 57 g (alticola and sclateri). Male nominate race has head and chest deep orange, contrasting black lores and chin to upper breast; upperparts orange, rather heavy black streaks on mantle and back; tail black, feathers with whitish tips, outer edge of outermost rectrix white; lesser upperwing-coverts orange, rest of upperwing black, median coverts broadly tipped white (prominent wingbar), greater coverts edged and tipped whitish (pale panel), flight-feathers edged whitish; underparts orange to orange-yellow; iris dark brown; bill black, basal half of lower mandible bluish-grey; legs bluish-grey. Female is similar to male, but slightly less richly coloured. Juvenile resembles dull female, but no black on lores and chin to breast, has crown olive-tinged, back greyer and almost unstreaked, less white in wing, dirty yellowish below; immature similar to female. Races differ mainly in intensity of bright coloration, amount of streaking on back, and size: microstictus is like ­nominate, but brighter, head and chest orange-yellow to fiery orange-red, black streaks above smaller, female sometimes duller and greener than male; graysonii has orange-yellow head, fewer black streaks on back; alticola has orange-yellow head, back so heavily streaked as to look solidly black; sclateri resembles previous in having orange-yellow head, but back is evenly streaked black and yellow; formosus resembles last, but smaller, and streaks above are in form of tear-shaped black spots; maximus is similar to alticola, but paler, more yellow than orange-yellow; pustuloides differs from nearby populations (sclateri) in smaller size and deep orange head.

Editor's Note: This article requires further editing work to merge existing content into the appropriate Subspecies sections. Please bear with us while this update takes place.

• Black-vented x Streak-backed Oriole (hybrid) Icterus wagleri x pustulatus

Editor's Note: Additional distribution information for this taxon can be found in the 'Subspecies' article above. In the future we will develop a range-wide distribution article.

Occupies canopy and edges of deciduous forest, swamps with palo verde (Parkinsonia aculeata) shrubs, thorny woodland and scrub, savannas, and trees at roadsides and villages. Occurs from lowlands up to c. 500 m; races maximus and alticola also range higher, locally reaching up to 2000 m. In El Salvador, pustuloides lives in xeric woodland at 800–1000 m, sometimes in nearby lowlands.

Apparently resident; in 1930s, race sclateri reported as making some local movements. Rare visitor in SW USA (Arizona, California).

Insects and other arthropods, also nectar and fruits. Two stomachs from El Salvador contained only insects. Gleans insects from foliage, and extracts larvae of beetles (Coleoptera) from rotten wood. Feeds on several fruits and arils of native plants. Takes nectar from flowers of the trees Erythrina breviflora, Erythrina oliviae and Pseudobombax ellipticum in Mexico, also from brush-like inflorescences of the vine Combretum fruticosum (individuals captured near the vine had pollen in plumage). Also catches bees (Apoidea) near flowers. Forages mostly in pairs and in family parties, occasionally in larger groups.

Song, by both sexes, mostly a melodic warbled series of whistles, somewhat like that of a vireo (Vireonidae), sometimes including dissonant “churr” notes; females usually sing less frequently than males. Common calls include chatters and a sharp “chit”.

Season May–Jul, later in N and at higher elevations. Probably largely monogamous; polygyny recorded. Solitary breeder. Nest a pensile bag 25–50 cm long, sometimes longer (to 70 cm), made from plant fibres and fungal rhizomorphs (reported as stealing nesting material from unguarded nests of conspecifics, and behaviour reciprocated by latter), placed rather high up in bush or tree, sometimes suspended from power line; often in thorny tree, including acacia (Acacia) species that harbour aggressive stinging ants (Formicidae), and reported also as nesting near wasp (Vespidae) nests; may nest in same tree with other orioles (mostly I. gularis, also I. pectoralis) and diverse birds, e.g. Rose-throated Becard (Pachyramphus aglaiae) and Campylorhynchus wrens. Clutch 3–4 eggs, rarely 5, white to pale blue with dark brown lines and blotches, mean dimensions 26 × 17·4 mm; incubation period 12–14 days; chicks fed by both sexes, nestling period c. 14 days. Nests are regularly parasitized by Molothrus aeneus, e.g. two of eleven nests in Oaxaca were parasitized; adults of present species have been reported feeding fledgling of Molothrus oryzivorus in Nicaragua.

Not globally threatened. Fairly common to common; locally rather abundant. Race microstictus, recorded very occasionally in SW USA, bred in Arizona in 1993 and subsequently in some years. The insular Tres Marías population (graysonii) deserves protection, because of its tiny global range and its distinctiveness.