JUVENAL PLUMAGE OF THE AZTEC THRUSH

KURT A. RADAMAKER, 16313 E. Crystal Point Dr., Fountain Hills, Arizona 85268; kurtrad@att.net

The monotypic Aztec Thrush (Ridgwayia pinicola) is endemic to Mexico (Howell and Webb 1995). It ranges from the mountains of central Chihuahua and Coahuila south to the Isthmus of Tehuantepec, favoring Madrean pine–oak woodland (Conservation International 2008) and pine forest from 1800 to 3500 m elevation (Howell and Webb 1995). Outside Mexico, it is casual in southeastern Arizona and southern Texas (AOU 1998). The secretive nature, irregular distribution, and nomadic habits of the Aztec Thrush make it difficult to study, leading to some uncertainty about its true status over much of its range. Also, little is known about its demography and life history; for example, the nests, eggs, and fledglings have rarely been observed.

On 1 September 2007 David Powell and I observed a recently fledged Aztec Thrush (see the photos featured on this issue’s back cover), along with an adult female. They were in a steep-walled ravine in Madrean pine–oak woodland with a small flowing creek, located off a cobblestone road above the restaurant and lodging at km 266 along Mexico Highway 16 at Mesa del Campanero, about 20 km west of the town of Yecora. This area is in a rugged region of the Sierra Oscura along the southern Chihuahua/Sonora border, surrounded by deep forested canyons (barrancas) typical of the higher reaches of the Sierra Madre Occidental. As we approached the ravine we flushed the birds from a large oak and noted the adult female carrying food. The juvenile, with only a partially grown tail (see top photo featured on this issue’s back cover), alighted nearby and allowed close approach, while the adult female was wary and kept mostly hidden. The adult stayed nearby and responded to pishing and mimicking of owl whistles by giving a raspy high-pitched “skree” call several times. The call was reminiscent of a Spotted Towhee (Pipilo maculatus) “shree” but higher pitched. The juvenile remained silent.

The juvenal plumage of the Aztec Thrush has rarely been photographed, is seldom depicted in field guides, and is infrequently encountered in the field. Outside of Mexico there is only one documented occurrence of a juvenile, of a bird photographed on 21 August 1977 at Boot Canyon, Big Bend National Park, Texas. Remarkably, that bird provided the first record for the United States (Wolf 1978). The juvenal plumage is quite different from the striking black and white of the adult and may offer some identification challenges. The overall ochraceous-buff appearance—combined with the heavily spotted/scaly breast and underparts, a characteristic shared with other juvenal-plumaged thrushes—could cause confusion, possibly with the juvenile Rufous-backed Robin (Turdus rufopalliatus) or American Robin (T. migratorius).

While there is potential for misidentification, with clear looks the identification is uncomplicated. Even with the noticeable differences from the adult in the contour feathers, on the bird we saw at Mesa del Campanero the black wings with contrasting white markings on the secondaries and primaries produced a subtle but clear resemblance to the adult. The resemblance was especially noticeable in flight. The color of the upperparts was sooty blackish brown with prominent ochraceous-buff streaking on the face, crown, nape, back, scapulars, and wing coverts. The coarse streaking on the crown formed a conspicuous supercilium, and the broad wedge-shaped spots of buff on the tips of the greater wing coverts formed a wide but broken lower wing bar. The breast and underparts were buff and heavily scalloped with black. The broad black margins to the feathers of the breast and underparts produced prominent spots. The eye was dark brown, the bill black, and the legs pink.

These photographs document only the second known nesting of the Aztec Thrush in Sonora and one of relatively few records of the species from that state. Russell and Monson (1998) cited just two reports, including one of an adult and three young birds on 17 September 1984, establishing the first breeding record for Sonora. Those birds were also near Mesa del Campanero. In fact, all Aztec Thrush sightings for Sonora of which I am aware come from the vicinity of Yecora, I suspect because of the area’s easy access via Mexico Highway 16. The 280 km of highway from Hermosillo to Yecora is a well known birding corridor, only a day’s drive from Nogales, Arizona.

A review of North American Birds (NAB) reports for the Aztec Thrush in Sonora since reporting began for Mexico in March of 2001 yielded a single report of 15 birds on 16 July 2006 at Yecora (NAB 60:584). However, I am aware of a few other sightings by birders who have visited Yecora, e.g., 5 birds on 10 July 2006 (Richard E. Webster pers. comm.), a lone female on 26 May 2008 (David Powell), and two winter reports: 12–15 birds on 19 December 1998 (Richard Palmer pers. comm.) and 25 birds on 20 December 1998 on the Yecora Christmas Bird Count (CBC). Forrest Davis (pers. comm.), compiler of the Yecora CBC, reports seeing the Aztec Thrush sporadically at Mesa del Campanero and in the surrounding barrancas above Yecora since 1990.

The status of the Aztec Thrush in Sonora, especially the northern limits of its breeding range and its status in winter, is not entirely clear. But the species is proving to be more regular in Sonora than the number of published records suggests. In Arizona there are approximately 20 accepted records, including several of multiple birds, e.g., up to nine in Madera Canyon, Santa Cruz County, 24 July 2006–7 August 2006. (Rosenberg and Witzeman. 1998, Rosenberg 2001, unpubl. data). There are four accepted records for Texas (Lockwood and Freeman 2004). Most of these sightings were during the summer monsoon season from July through September; there are only two acceptable reports in winter. This pattern of occurrence in Arizona and Texas appears to coincide with the species’ status in Sonora. Phillips (1991) suggested that summer residents withdraw from northwestern Mexico from October through February; Howell and Webb (1995) reported that the Aztec Thrush occurs in winter north at least to Sinaloa. Given the two winter reports of sizable flocks at Yecora, evidently it occasionally winters in Sonora as well.

In Sonora the Aztec Thrush should be considered a rare and local summer resident and casual winter visitant to the higher Madrean pine–oak woodlands and pine forests of the Sierra Madre Occidental.

I thank Richard E. Webster, David Powell, Cindy Radamaker, Forrest Davis, Richard Palmer, Mark M. Stevenson, Richard A. Erickson, and Osvel Hinojosa for helpful comments and suggestions.

LITERATURE CITED

American Ornithologists’ Union. 1998. Check-list of North American Birds, 7th ed. Am. Ornithol. Union, Washington, D.C.

Conservation International. 2008. Biodiversity Hotspots. www.biodiversity hotspots.org/xp/Hotspots/pine_oak/Pages/default.aspx (12 July 2008).

Howell, S. N. G., and Webb, S. 1995. A Guide to the Birds of Mexico and Northern Central America. Oxford Univ. Press, Oxford, England.

Lockwood, M. W., and Freeman, B. 2004. The TOS Handbook of Texas Birds. Texas A & M Univ. Press, College Station.

Phillips, A. R. 1991. The Known Birds of North and Middle America, Part 2. A. R. Phillips, Denver.

Rosenberg, G. H. 2001. Arizona Bird Committee report: 1996–1999 records. W. Birds 32:50–70. 

Rosenberg, G. H., and Witzeman, J. L. 1998. Arizona Bird Committee report, 1974–1996: Part 2 (passerines). W. Birds 30:94–120.

Russell, S. M., and Monson, G. 1998. The Birds of Sonora. Univ. of Arizona Press, Tucson.

Wolf, D. 1978. First record of Aztec Thrush in the United States. Am. Birds 32:156–157.