Plumages, Molts, and Structure

The Horned Screamer has 10 functional primaries (numbered distally, from innermost p1 to outermost p10), 15-17 secondaries (numbered proximally, from innermost s1 to outermost s12-s14 and including three tertials numbered distally, from t1 to t3), and 12 rectrices (numbered distally on each side of the tail from innermost r1 to outermost r6). Lower scapulars are broad and elongated to cover the tail. Little or no geographic variation in appearance has been reported (see Systematics). See Molts for molt and plumage terminology. The following is based primarily on plumage descriptions in Blake (1 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 ), Todd (2 Todd, F. S. (1979). Waterfowl: Ducks, Geese & Swans of the World. Harcourt Brace, New York, NY, USA. Close ), Carboneras (3 Carboneras, C. (1992). Family Anhimidae (screamers). In Handbook of the Birds of the World, Volume 1 (J. del Hoyo, A. Elliott, and J. Sargatal, Editors), Lynx Edicions, Barcelona, Spain. pp. 528–535. Close ), and Kear (4 Kear, J., Editor (2005). Ducks, Geese and Swans. Oxford University Press, Oxford, UK. Close ), along with examination of Macaulay Library images. Sexes appear similar in all plumages; definitive appearance appears to be assumed at the Third to Fourth Basic plumage, but further study is needed. Timing of plumages generally may revolve around a peak breeding season of November-May, but fresh and worn examples of all plumages likely can be found year-round (see Breeding: Phenology).

Natal Down

Hatchlings are described as yellow above and white below (4 Kear, J., Editor (2005). Ducks, Geese and Swans. Oxford University Press, Oxford, UK. Close ). Examination of Macaulay Library images (see below) confirms that a first natal down is primarily yellowish and a second natal down develops that is brownish black above and grayish below.

Juvenile (First Basic) Plumage

Juvenile Plumage is like later plumages but washed brown, the head primarily dark and the white markings to the neck and wing coverts reduced and duller. Upperpart feathers, wing coverts, and flight feathers are uniform in wear, without molt-related variation. Juvenile head and neck feathers are filamentous due to lower barb densities, and scapulars, upperwing coverts, remiges, and rectrices are narrower and more rounded or tapered at the tips than those of later plumages, duller black or only slightly glossy (scapulars, lesser, and median coverts). The juvenile outer primary (p10) is tapered or pointed at the tip, rather than squared or outwardly curved as in basic feathers. See also Bare Parts for changes in iris color and cartilaginous horn and wing spur development with age.

Formative Plumage

Formative Plumage is like Definitive Basic Plumage but averages duller and browner. Body feathering is primarily formative, duller than basic body feathering, and usually with some worn and brownish juvenile feathers retained among the upperparts, neck, and lower underparts. Molt limits occur between glossier replaced formative back feathers and duller and browner retained juvenile upperwing coverts. Look for some birds to replace some inner secondary coverts and possibly 1-2 tertials as well. Retained juvenile remiges and rectrices are otherwise narrow, brown, and tapered or pointed at the tips, including the outer primary (p10). See also Bare Parts for changes in iris color and cartilaginous horn and wing spur development that can be helpful for ageing.

Second and Third Basic Plumages

Examination of Macaulay Library images indicates that this species undergoes Staffelmauser (see Definitive Basic Plumage). Following the incomplete Second Prebasic Molt, a few formative (and possibly juvenile) body feathers may be retained, worn and brown relative to retained basic feathers of older birds. Replacement of juvenile remiges appears usually to be incomplete, with up to five or more juvenile outer primaries and some to most juvenile secondaries in the center of the tract retained, narrow, brown, and worn, contrasting with replaced, glossy black inner primaries, tertials, and outer secondaries. One or more juvenile rectrices may also be retained, perhaps most commonly among r3-r5. It may be possible that juvenile feathers may also be retained during the Third Prebasic Molt, perhaps 1-2 outer primaries (among p9-p10) and one to a few middle secondaries (among s3-s8), contrasting with two generations of basic feathers replaced in sequence (see Molts). Study is needed on variation in molt extents and the ability to identified these two plumages in Horned Screamer. See also Bare Parts for changes in iris color and cartilaginous horn and wing spur development that can be helpful for ageing.

Definitive Basic Plumage

Head mostly black, the top of the head speckled white, showing substantial variation in extent, from the crown to the sides of the head, allowing identification of individuals (5 Naranjo, L. G. (1986). Aspects of the biology of the Horned Screamer in southwestern Colombia. Wilson Bulletin 98(2):243–256. Close ). The feathers of the nape, lower neck, and upper breast are white, broadly and sharply tipped black; these feathers can be extended to form a ruff with striking scaled appearance. Remaining upperpart feathers (including elongated lower scapulars) and rectrices glossy black when fresh, fading to brownish black when worn. Upperwing marginal lesser coverts white, forming distinct white triangles on the inner portions of the open wings from above; lower lesser coverts glossy black to brownish black with variable white bases, inner webs, and/or shaft streaks; median and greater coverts entirely black or variably with some white on the inner webs or thin white shaft streaks. Primary coverts and remiges glossy black to brownish black, the bases to the coverts and primaries with white extending distally on the edges each web, most extensively among the inner primaries. Lower neck and center breast glossy black forming a broad breast band that extends and thins ventrally along flanks; belly, ventral feathering, femoral feathering, and undertail coverts white. Underwing coverts black with brownish or gray margins, broader on the lesser and median coverts.

Incomplete and/or protracted molts result in mixed generations or levels of wear among fresher and glossier black and more worn and browner body feathers and upperwing coverts producing a mixed pattern of wear that differs from the uniform feathering of Juvenile Plumage. Basic remiges and rectrices are broader and blacker than juvenile feathers retained in Formative and Second Basic Plumages, the tips truncated and the outer primary curved inward at the tip. Remiges typically show 2‒4 sets of basic feathers in Staffelmauser (or stepwise) patterns (see Molts), the number of sets (defined by a more worn feather distal to a fresher feather) signifying minimum age up to at least Fourth or Fifth Basic Plumage, as in other large birds that undergo Staffelmauser (6 Pyle, P. (2006). Staffelmauser and other adaptive strategies for wing molt in larger birds. Western Birds 37(3):179–185. Close , 7 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ). See also Bare Parts for changes in iris color and cartilaginous horn and wing spur development that can be helpful for ageing.

General

Molt and plumage terminology follows Humphrey and Parkes (8 Humphrey, P. S., and K. C. Parkes (1959). An approach to the study of molts and plumages. The Auk 76(1):1–31. Close ), as modified by Howell et al. (9 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 ). Under this nomenclature, terminology is based on evolution of molts along ancestral lineages of birds from ecdysis (molts) of reptiles, rather than on molts relative to location or time of the year (see 7 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ,10 Pyle, P. (2022). Defining moults in migratory birds: a sequence-based approach. Journal of Avian Biology 2022(5):e02958. Close for more information). Little information has been published on molts in the Horned Screamer although remiges are known to molt sequentially rather than synchronously resulting in flightless periods as occurs in most other Anseriformes (11 Stresemann, E., and V. Stresemann (1966). Die Mauser der Vögel. Journal für Ornithologie 107, Sonderheft. Close ,12 Haffer, J. (1968). Notes on the wing and tail molt of the screamers and Sunbittern and immature guans. Auk. 85(4):633–638. Close ,4 Kear, J., Editor (2005). Ducks, Geese and Swans. Oxford University Press, Oxford, UK. Close ). Based on examination of Macaulay Library images, Horned Screamer appears to exhibit a Complex Basic Strategy (cf. 9 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 , 13 Howell, S. N. G. (2010). Molt in North American Birds. Houghton Mifflin Harcourt, Boston, MA and New York, NY, USA. Close ), including incomplete prebasic molts and a partial preformative molt but no prealternate molts. Remigial replacement undergoes Staffelmauser (or stepwise) molting patterns. Timing of molts may generally follow the peak breeding season of November-May (see Breeding: Phenology) but replacement of flight feathers appears to be protracted and likely can be found throughout much of the year within individuals and year-round at the population level.

Prejuvenile (First Prebasic) Molt

Complete in or near the natal territory. No detailed information on this molt in Horned Screamer.

Preformative Molt

Examination of Macaulay Library images indicates that the Preformative Molt is limited to partial, similar in extent to other large Anseriformes (e.g., geese and swans; 7 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ), including some to most body feathers, with some juvenile feathers often retained, most commonly among scapulars, rump feathers, and lower underparts; perhaps some inner upperwing secondary coverts or rarely one or more teritals can also be replaced (see images under Formative Plumage). Molt may be protracted, occurring from 2 to 10 months following fledging, as in other large Anseriformes, with longer scapulars and tertials (if replaced) molted last.

Second and Third Prebasic Molts

Examination of Macaulay Library images indicates that prebasic molts are usually if not always incomplete. Replacement of juvenile body feathers and upperwing coverts often incomplete, resulting in mixed juvenile and basic feathers in second and perhaps sometimes third basic plumage. Sequence of flight-feather replacement as in definitive prebasic molt. Following the Second Prebasic Molt, up to five or more juvenile outer primaries and corresponding primary coverts, and 6-10 or more juvenile secondaries in the center of the tract may often be retained. Staffelmauser (stepwise) replacement patterns (11 Stresemann, E., and V. Stresemann (1966). Die Mauser der Vögel. Journal für Ornithologie 107, Sonderheft. Close , 6 Pyle, P. (2006). Staffelmauser and other adaptive strategies for wing molt in larger birds. Western Birds 37(3):179–185. Close , 7 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ) ensue (see below), the Third Prebasic Molt commencing where Second Prebasic Molt arrested and new sequences sometimes commencing at p1 and the tertials (see images under Second and Third Basic Plumages). During these initial remigial molts, symmetry is usually maintained between the wings but patterns can begin to become asymmetrical following the Third Prebasic Molt.

Definitive Prebasic Molt

Usually if not always incomplete; non-breeding birds may typically molt more feathers than breeding adults due to lack of breeding constraints. A high proportion of Macaulay images show birds replacing primaries, indicating that molt may be protracted, occurring rather continuously apart from breeding. Most to many body feathers, upperwing coverts, and rectrices are usually replaced every year, but many feathers may be retained; primaries and secondaries are usually (if not always) partially replaced every year. Primaries are replaced distally (p1 to p10), secondaries appear to be replaced convergently, distally from the tertials (perhaps most often bilaterally from the middle tertial, t2) followed by a proximal wave commencing at s1, and rectrices may generally be replaced distally on each side of the tail, although the outer rectrix appears to be molted before feathers among r3-r5 as is common in large birds such as raptors.

Molting patterns among primaries and secondaries exhibit Staffelmauser (11 Stresemann, E., and V. Stresemann (1966). Die Mauser der Vögel. Journal für Ornithologie 107, Sonderheft. Close , 6 Pyle, P. (2006). Staffelmauser and other adaptive strategies for wing molt in larger birds. Western Birds 37(3):179–185. Close , 7 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ) whereby incomplete molts result is a series of commencement points, beginning with termination points of previous prebasic molt and also initiating new series commencing at p1, the tertials, and s1. Replacement thus typically proceeds in 2–4 waves through the wing. After several years replacement patterns can become quite asymmetrical between the wings. Staffelmauser appears to be a product of insufficient time to undergo a complete wing-feather molt but has adaptive benefits in producing multiple small gaps in the wing during molt, which retains wing integrity and ability to fly and forage (14 Tucker, V. A. (1991). The effect of molting on the gliding performance of a Harris' Hawk (Parabuteo unicinctus). Auk 108:108–113. Close , 15 Shugart, G. W., and S. Rohwer (1996). Serial descendant primary molt or Staffelmauser in Black-crowned Night-Herons. Condor 98:222–233. Close , 16 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 ).

Study may be needed on replacement sequence of the secondaries, which do not appear to have a node at s5 as in other large diastataxic birds that undergo Staffelmauser (7 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ). Primaries reportedly molted from several nodes (11 Stresemann, E., and V. Stresemann (1966). Die Mauser der Vögel. Journal für Ornithologie 107, Sonderheft. Close , 12 Haffer, J. (1968). Notes on the wing and tail molt of the screamers and Sunbittern and immature guans. Auk. 85(4):633–638. Close ) but examination of Macaulay Library images indicates typical distal replacement with initiation points depending on previous incomplete molts (see images below and under Definitive Basic Plumage).

The following is based on Herklots (17 Herklots, G. A. C. (1961). The birds of Trinidad and Tobago. Collins, London, UK. Close ), Blake (1 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 ), and Kear (4 Kear, J., Editor (2005). Ducks, Geese and Swans. Oxford University Press, Oxford, UK. Close ) along with examination of Macaulay Library images to evaluate changes in bare-part coloration and structure with age.

Bill

In adults, the bill is brownish to blackish. In nestlings, it is paler bluish gray (see images under Natal Down), quickly becoming brownish in juveniles.

Iris and Facial Skin

In adults, the iris varies from deep yellowish to orange or red. In many pairs shown in Macaulay Library images, the iris is washed more heavily with orange or red in one of the two birds (see, e.g., below and ML189021921 , ML412000801 ), suggesting that males may get redder irides than females, as occurs in some raptors such as those in genus Accipiter (7 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close ); study is needed on this. In hatchlings the iris is dark, gradually becoming gray or yellowish gray in Juveniles and pale yellow during the first year (see images under Natal Down, Juvenile Plumage, and Formative Plumage). The orbital and loral skin is grayish (tinged bluish or pinkish in younger birds) to black in some adults.

Tarsi and Toes

At all ages, the tarsi and toes can be grayish brown, brownish yellow, or ash gray, potentially averaging pinker at younger ages.

Horn and Spurs

An unusual character of the Horned Screamer is the spiny, cartilaginous, pale-yellow to ivory "horn" or spike protruding forward from the forecrown, which can be up to 150 mm in length (4 Kear, J., Editor (2005). Ducks, Geese and Swans. Oxford University Press, Oxford, UK. Close ). The horn is absent in nestlings and juveniles, and develops during the first year (while in Formative Plumage), being thin and straight at first. The length of the horn may indicate age, with older birds developing longer and more curved or sinuate horns. There also are two spurs on the manus (fused metacarpals) at the bend of the wing; the more proximal spur is the larger, and can be up to 60 mm long (18 Rand, A. L. (1954). On the spurs on birds’ wings. Wilson Bulletin 66:127–134. Close ). The wing spurs are gray with pale ivory tips, and are also absent in nestlings and juveniles. The spurs develop during the first year, and continue to develop and become thicker and stronger in older individuals.

Linear Measurements

Bill Length (Culmen, 1 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 )

• female: mean 51.7 mm (range 49–55 mm, n = 9)
• male: mean 52.2 mm (range 49–55 mm, n = 10)

Wing Length (Flat, 1 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 )

• female: mean 548.7 mm (range 504–590 mm, n = 9)
• male: mean 545.1 mm (range 482–585 mm, n = 10)

Tail Length

• female: mean 260.4 mm (range 216–305 mm, n = 9)
• male: mean 256.4 mm (range 214–293 mm, n = 10)

Spurs (18 Rand, A. L. (1954). On the spurs on birds’ wings. Wilson Bulletin 66:127–134. Close )

• female: proximal spur: 50–55 mm; distal spur: 11–17 mm
• male: proximal spur: 58-61 mm; distal spur: 15–16 mm

Mass

• 3,000–3,150 g (3 Carboneras, C. (1992). Family Anhimidae (screamers). In Handbook of the Birds of the World, Volume 1 (J. del Hoyo, A. Elliott, and J. Sargatal, Editors), Lynx Edicions, Barcelona, Spain. pp. 528–535. Close , 4 Kear, J., Editor (2005). Ducks, Geese and Swans. Oxford University Press, Oxford, UK. Close ); 3,150 g (19 Sick, H. (1993). Birds in Brazil: A Natural History. Princeton University Press, Princeton, NJ, USA. Close )