Plumages, Molts, and Structure

The Andean Ibis has 10 full-length primaries (numbered distally, from innermost p1 to outermost p10), 13–14 secondaries (numbered proximally, from outermost s1 to innermost s10, and including 3–4 tertials, numbered distally, t1 to t3 or t4), and 12 rectrices (numbered distally, from innermost r1 to outermost r6 on each side of the tail). Little or no geographic variation in appearance is reported (see Systematics). See Molts for molt and plumage terminology and for the possible occurrence of alternate plumages in this species. The following is based primarily on detailed plumage descriptions in Blake (2 Blake, E. R. (1977). Manual of Neotropical Birds. Volume 1. Spheniscidae (Penguins) to Laridae (Gulls and Allies). The University of Chicago Press, Chicago, IL, USA, and London, UK. Close ), Hancock et al. (3 Hancock, J. A., J. A. Kushlan, and M. P. Kahl (1992). Storks, Ibises and Spoonbills of the World. Academic Press, London. Close ), Matheu and del Hoyo (4 Matheu, E., and J. del Hoyo (1992). Family Threskiornithidae (ibises and spoonbills). In Handbook of the Birds of the World, Volume 1: Ostrich to Ducks (J. del Hoyo, A. Elliott, and J. Sargatal, Editors). Lynx Edicions, Barcelona, Spain. pp. 472-507. Close ), and Collar and Bird (1 Collar, N. J., and J. P. Bird (2011). Phenotypic discrimination of the Andean Ibis (Theristicus branickii). Wilson Journal of Ornithology 123(3):459–463. Close ), along with examination of images in Macaulay Library; see Pyle (5 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ) for age/sex-related criteria in other ibises. Definitive appearance may typically be assumed at the Third or Fourth Basic Plumage; study needed (see below). Sexes are similar in all plumages.

Natal Down

Present primarily November–January, at the nest site. Natal down not described for Andean Ibis. Examination of Macaulay Library images (see below) indicates that it may be primarily grayish above and buff below, with dusky lower underparts and femoral feathering, mimicking later plumages.

Juvenile (First Basic) Plumage

Present primarily January–March. Juvenile Plumage is similar to later plumages but duller and browner in the head, neck, and breast. Crown gray-brown; nape and sides of head whitish to buff, whitest on auriculars. Remainder of upperparts dark gray, the feathers tipped buff when fresh. Upperwing lesser coverts buff with grayish centers creating scaled appearance; median and greater coverts washed brownish and with broad buff tips and often shaft streaks. Breast buff becoming whiter ventrally, some feathers often with narrow streaks. Flight feathers as in Definitive Basic Plumage except narrower, more rounded or tapered at the tips, and browner.

Formative Plumage

Present primarily February (when fresh) to October (when worn). Similar to Definitive Basic Plumage except browner, duller, and with the neck pale buff, prominently streaked dark brown. Back feathers and sometimes upperwing coverts mixed with worn brown Juvenile and fresher grayer Formative feathers. Streaked Juvenile lower breast feathers often retained. Juvenile flight feathers retained and, by June–September, become worn and abraded, brown, narrow, and tapered or rounded at the tips. Primaries and secondaries lack molt clines or contrasts in feather generations of Definitive Basic Plumage (see below).

Second and Third Basic Plumages

Present primarily April (when fresh) to November (when worn). It appears that at least some birds in Second Basic Plumage and perhaps occasional birds in Third Basic Plumage may retain Juvenile flight feathers but study is needed. Retained Juvenile outer primaries during the Second Prebasic Molt may include up to 6 feathers among p5–p10, and retained Juvenile secondaries would typically be among s2–s4 and s6–s10 in Second Basic Plumage and s3-s4 and s8-s9 in Third Basic Plumage. One or more Juvenile rectrices may also be retained in some Second Basic birds; study needed. Body plumage appears similar to that of Definitive Basic Plumage, although birds in Second Basic Plumage may average less rufous-brown to the breast and with a less-distinct black breast collar.

Definitive Basic Plumage

Present primarily May (when fresh) to November (when worn). Crown, upper nape, and and upper face rufous-brown or chestnut; hindnape, malar area, and sides of neck buff, tinged rufous when fresh; upper back, scapulars, upperwing secondary coverts, and tertials bluish-gray when fresh; lower back feathers become dusky, the feathers tipped with gray; rump blackish; uppertail coverts and tail black, the rectrices glossed greenish when fresh. Primary coverts, primaries, and secondaries black, tinged glossy green when fresh. Chin and throat buff, becoming tinged then washed with chestnut on lower breast; grayish to dusky feathering extends from upper back across breast to form U-shaped collar; abdomen feathers below collar whitish-buff; ventral feathering, undertail coverts, femoral feathering, and underwing coverts black. Extent of chestnut, buff, and whitish to the head and underparts shows individual variation. Plumage of upperparts changes with wear; the back feathers, wing coverts, and scapulars become darker gray with dusky centers and the head and breast sometimes bleaching to whitish when worn.

Definitive Basic Plumage separated from earlier plumages by showing basic flight feathers, which are blackish (when fresh), broad, and more truncate at the tips than retained Juvenile feathers. Clines in freshness are evident between earlier replaced (browner) and later replaced (blacker and glossier) remiges. Evidence from Macaulay Library images indicates that Andean Ibis undergoes Stafflemauser (or stepwise) molting patterns (see Molts) and can show up to four "sets" of basic primaries, a set defined by older outer next to newer inner primaries; the number of sets indicates minimum age (6 Pyle, P. (2006). Staffelmauser and other adaptive strategies for wing molt in larger birds. Western Birds 37:179–185. Close , 5 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ).

General

Molt and plumage terminology follows Humphrey and Parkes (7 Humphrey, P. S., and K. C. Parkes (1959). An approach to the study of molts and plumages. Auk 76(1):1–31. Close ), as modified by Howell et al. (8 Howell, S. N. G., C. Corben, P. Pyle, and D. I. Rogers (2003). The first basic problem: a review of molt and plumage homologies. Condor 105:635–653. Close ). Andean Ibis may exhibit either a Complex Basic Strategy (see8 Howell, S. N. G., C. Corben, P. Pyle, and D. I. Rogers (2003). The first basic problem: a review of molt and plumage homologies. Condor 105:635–653. Close , 9 Howell, S. N. G. (2010). Peterson Reference Guide to Molt in North American Birds. Houghton Mifflin Harcourt, Boston, MA, USA. Close ), including incomplete Prebasic Molts and a limited-to-partial Preformative Molt but no prealternate molts or a Simple Alternate Strategy including prealternate molts in the second and later cycles but not the first cycle as in other ibises (5 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ). Examination of Macaulay Library images indicates substantial variation in wear levels of back feathers of breeding adults, which could indicate the presence of a limited Definitive Prealternate Molt in September–October in at least some individual Andean Ibises; further study on the possible occurrence of this molt is needed.

Prejuvenile (First Prebasic) Molt

Complete, primarily December–February, in the nest. Details on growth of Juvenile plumage Andean Ibis is unknown. Macaulay Library images (e.g., see Juvenile Plumage) indicates that upperwing coverts and flight feathers erupt prior to most body feathers.

Preformative Molt

Limited to partial, primarily February–May, but may be protracted to July or later. Includes feathers of the head and scattered feathers of the back, perhaps also occasionally some lesser or other upperwing secondary coverts. Study needed on the extent of this molt.

Second and Third Prebasic Molts

Incomplete, primarily October–February but possibly protracted into June or later for some individuals. The Second Prebasic Molt may average earlier than later prebasic molts due to lack of time constraints for breeding. Study is needed but examination of Macaulay Library images indicates that the Second Prebasic Molt may often be incomplete, including a variable number of inner primaries (and corresponding primary coverts) and secondaries, but not all feathers. Retained Juvenile feathers may include outer primaries among p6–p10 and secondaries among s3–s4 and s7–s11; some upperwing coverts and rectrices may also be retained. It may be possible that the Juvenile p10 and 2–3 secondaries (among s4 and s8–s9) may continue to be retained following the Third Prebasic Molt. These extents for the Second and Third Prebasic Molt are consistent with other species that can show up to four sets of primaries in Staffelmauser patterns (see below). See images under Second and Third Basic Plumages.

Definitive Prebasic Molt

Incomplete, primarily February–July but possibly protracted into September or later for some individuals; study is needed as few images are present of birds undergoing flight-feather molt in Macaulay Library. Most to all body feathers and upperwing secondary coverts are replaced but molt of flight feathers is usually incomplete; examination of Macaulay Library images indicates little or no evidence for complete prebasic molts, but it might be expected to occur in occasional individuals. Variation in wear of back feathers indicates molt of this tract may be protracted and/or suspended, but may also indicate the presence of a Definitive Alternate Plumage as in other ibises; study is needed.

Primaries are replaced distally (from innermost p1 to outermost p10), secondaries are replaced proximally from s1 and s5 and distally from the tertials (often bilaterally from t2), and the rectrices may generally be replaced distally (from inner r1 to outer r6) on each side of the tail, with some variation in this sequence possible. Staffelmauser molting patterns appear to occur in most to all individuals, whereby remiges molt in sequence, resuming from the point in which the previous incomplete molt was arrested, and also commencing with a new series of molt at p1, s1, s5, and the tertials, resulting in up to four waves of replacement within both primary and secondary tracts (see 6 Pyle, P. (2006). Staffelmauser and other adaptive strategies for wing molt in larger birds. Western Birds 37:179–185. Close , 5 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ; see images under Definitive Basic Plumage). Staffelmauser molting patterns occur when large birds lack the time to complete flight-feather molt in a single year, and it has the ultimate benefit of preventing larger gaps in the wing, enabling flight and foraging during peak molting periods (10 Pyle, P. (2005). Remigial molt patterns in North American Falconiformes as related to age, sex, breeding status, and life-history strategies. Condor 107(4):823–834. Close ).

Bill

The bill is long and decurved but generally less so in Andean Ibis than in most ibises, which need longer bills for feeding in water. In nestlings and juveniles, the bill is slate with a dull greenish distal half. In adults, the bill can be dark slate to black, sometimes tinged horn at the base and tipped with dull greenish. Slit-like nostrils are present at the base of the bill to allow feeding in water and mud (4 Matheu, E., and J. del Hoyo (1992). Family Threskiornithidae (ibises and spoonbills). In Handbook of the Birds of the World, Volume 1: Ostrich to Ducks (J. del Hoyo, A. Elliott, and J. Sargatal, Editors). Lynx Edicions, Barcelona, Spain. pp. 472-507. Close ).

Iris and Facial Skin

In nestlings and juveniles, the iris is dull brownish, gradually becoming warmer brown during the first year. In adults the iris is dark red. Bare orbital skin is slate, and adults show triangular strips of bare black skin extending from the bill in the malar area on both sides. These bare strips are feathered in nestling and juveniles and begin to become exposed during the first year of age.

Tarsi and Toes

In nestlings and juveniles, legs and feet are gray to slate, gradually becoming dusky-pink to dull reddish in the first year. In adults, legs and feet are red, perhaps becoming brighter during the courting and breeding periods and duller during molt and in the non-breeding season.

Linear Measurements

All values presented as mean ± standard deviation, and come from Collar and Bird (1 Collar, N. J., and J. P. Bird (2011). Phenotypic discrimination of the Andean Ibis (Theristicus branickii). Wilson Journal of Ornithology 123(3):459–463. Close ) unless otherwise noted.

Bill Length

118.4 cm ± 8.011 (range 105–130 cm; n = 29).

Tarsus Length

69.0 cm ± 3.914 (range 60–75 cm; n = 32).

Wing Length

391.0 cm ± 10.855 (range 369–409 cm; n = 32).

Tail Length

215.4 cm ± 9.922 (range 200–238 cm; n = 31).

Mass

Information needed.

Wing Area, Wing Aspect Ratio, Wing Loading

Information needed.