Icterus graduacauda

Audubon’s Oriole is a poorly known but brightly colored bird found only in Mexico and southern Texas. It now occurs mainly in larger, more remote tracts of brushland and forest, in the South Texas brush country and in the mountains of Mexico. Because of its secretive nature, Audubon’s Orioles are hard to find, and its breeding habits and precise distribution and abundance are poorly known. Very little work has been done on this species, with the notable exception of Flood (1990).

In Texas, Audubon’s Orioles occur in the Tamaulipan Biotic Province, also known as the South Texas brush country or Rio Grande Plain. Although a year-round resident, individuals wander into more densely populated agricultural areas during the winter. Generally a shy bird, Audubon’s Orioles will visit seed-feeders, especially outside the breeding season. The species is on the National Audubon Society Watchlist, indicating concern about its limited range and poorly known population status.

DISTRIBUTION: TBBAP records and information from other observers show that Audubon’s Oriole occurs from Webb, Frio, McMullen, and Karnes Counties (latilongs 28099, 28098, and 28097) south to Zapata, Starr, extreme western Hidalgo Counties (26099 and 26098), and southern Kenedy County (26097-F5). The range has apparently retracted from historical populations in Val Verde, Bexar (non-breeding only), Nueces, Cameron and much of Hidalgo Counties. It was a fairly common breeder in Cameron and Hidalgo Counties between the 1870s and 1920s, but has been noted as rare since 1960 (Oberholser 1974). Only one pair was present on Santa Ana National Wildlife Refuge (26098-A2) during Gehlbach’s 1973-1977 breeding bird community study (Gehlbach 1987), and it is now a rare winter wanderer there and in most of the Lower Rio Grande Valley. The best-known population in Texas (since the 1970s) is along the Rio Grande in southwestern Starr County (26099-E1,E2), but recently a population has been found in Kenedy County (26097-F5, G5)(Fall 1973, Wauer et al. 1993).

SEASONAL OCCURRENCE: Individuals and pairs can be found all year throughout the range, suggesting that most individuals are sedentary.

However, occurrence may be erratic, especially at the edge of the range (Vega & Rappole 1994; T. Brush, pers. obs.), suggesting that some individuals may shift in response to drought and/or cold weather. The potential breeding season is quite long, from late March through September, although most birds may breed between April and July. However, the breeding season is poorly known, with only three nests seen during the TBBAP years (27097-D8, 26099-H3, 26098-B4). The nest at 27097-D8 was a long, sac-like nest apparently made by the Altamira Oriole (I. gularis) member of mixed Audubon’s/Altamira pair, found on 27 June 1988 by Paul Palmer. Audubon’s Oriole nests are semi-pensile cups (Flood 1990).

BREEDING HABITAT: Despite its limited range and apparently low population density, Audubon’s Oriole is a habitat generalist,  occurring in dense mesquite forest, other thorn-forest and thorn-scrub, riparian forest, and oak forest. A relatively undisturbed forest with a dense layer of foliage may be a common feature of breeding habitat (B. Ortego, pers. comm., T. Brush, pers. obs.). Nests are usually hidden in dense foliage. They may be only 2-4 m (6-13 ft) up in the lower foliage of a mesquite forest (Bendire 1895), but they would likely be higher in taller riparian or oak forests (Flood 1990).

STATUS: Audubon’s Oriole was first found in Texas in 1838 (Bendire 1895). The species was long thought to be limited mainly to the Lower Rio Grande Valley area, where most early observations were made (Sennett 1878, 1879). This probably reflects primarily a lack of attention to the species in the northern and central sections of its current Texas range, since the species nested in Del Rio (latilong 29100) in 1941, and 8-10 birds were seen in Bexar County (29098) in February 1891 (Attwater 1892). The historic status in the oak forests of latilong 26097 is poorly known, but species probably has increased there during this century, due to the larger amount of oak forest now present on the sand plain (Fall 1973).

Although no quantitative studies have been done, Audubon’s Oriole may require large tracts of forest or brush to maintain viable populations. In the Lower Rio Grande Valley, and also probably in Nueces (27097)and Val Verde Counties (29100), the loss of much habitat and the fragmentation of remaining habitat has probably been the cause of Audubon’s Oriole declines. This species frequently raises Bronzed Cowbirds (Molothrus aeneus) instead of its own young (Bendire 1895, Friedmann 1963, Flood 1990), and also is parasitized by Brown-headed Cowbirds (M. ater). Such data suggest that Audubon’s Oriole may be one of the species hardest hit by brood parasitism in southern Texas, especially in the Lower Rio Grande Valley where Bronzed Cowbird populations are extremely high (C. Hathcock and T. Brush, unpubl. data). The ability of Audubon’s Orioles to persist in less disturbed ranchlands should be studied further, since both species of cowbirds are also present in those areas. Text by Tim Brush (ca. 1995)

Literature cited
Attwater, H. P.  1892.   List of birds observed in the vicinity of San Antonio, Bexar Co., Texas.  Auk 9: 229-238.

Bendire, C.  1895.   Life histories of North American birds.   U.S. Nat. Mus. Spec. Bull. 3.

Fall, B. A.  1973.   Noteworthy bird records from South Texas (Kenedy Co.).  Southwestern Naturalist 18: 244-247.

Flood, N. J. 1990.  Aspects of the breeding biology of Audubon’s Oriole.  J. Field Ornithol. 61: 290-302.

Friedmann, H.  1963.   Host relations of the parasitic cowbirds.   U.S. Nat. Mus. Bull. 233.

Gehlbach, F. R.  1987.   Natural history sketches, densities, and biomass of breeding birds in evergreen forests of the Rio Grande, Texas, and the Rio Corona, Tamaulipas, Mexico.  Texas J. Sci. 39:241-251.

Oberholser, H. C.  1974.   The bird life of Texas. Vol. 2.  Univ. of Texas Press, Austin.

Sennett, H. B.  1878.   Notes on the ornithology of the lower Rio Grande of Texas, from observations made during the spring of 1877.  Bull. Geol. Geogr. Surv. Terr. 4: 1-66.

Sennett, H. B.  1879.   Further notes on the ornithology of the lower Rio Grande of Texas, from observations made during the spring of 1878.  Bull. Geol. Geogr. Surv. Terr. 5: 377-440.

Vega, J. H. and J. H. Rappole.  1994.  Composition and phenology of an avian community in the Rio Grande Plain of Texas.  Wilson Bull. 106: 366-380.

Wauer, R. H., P. C. Palmer, and A. Windham.  1993.  The Ferruginous Pygmy-Owl in South Texas.  Am. Birds 47: 1071-1076.