Plumages, Molts, and Structure

South African Shelducks have 10 full-length primaries (numbered distally, from innermost p1 to outermost p10), about 18 secondaries (numbered proximally, from outermost s1 to innermost s15 and including 3 tertials, numbered distally t1 to t3), and typically 14 rectrices (numbered distally from innermost r1 to outermost r7 on each side of the tail. Little or no geographic variation in appearance has been reported (see Systematics). See Molts for terminology on molts and plumages.

Natal Down

Completely downy when hatched. Natal down is strikingly patterned, brown with white cheeks and underparts (contrasting sharply with brown crown) and distinct white patches on the sides of the back, sides of the rump, and wings. Male chicks are reported to have paler-colored breasts than females, but this difference may not be readily apparent in the field (1 Geldenhuys, J. N. (1980). Breeding ecology of the South African shelduck in the southern Orange Free State. South African Journal of Wildlife Research 10:94–111. Close ).

Juvenile (First Basic) Plumage

In Juvenile Plumage, both sexes resemble the adult male but are duller, with browner heads, auriculars, and necks, usually some white on the eyebrow, and extensive dusky brown on the white wing-coverts (2 Shewell, A. L. (1959). The waterfowl of Barberspan. Ostrich Supplement 3:160–179. Close ). That juveniles resemble males is unusual among sexually dimorphic birds, but accords with the partially reversed coloration and sexual roles in this species (3 Maclean, G. L., and G. Darroll (1986). Ducks of Sub-Saharan Africa. Acorn Books, Johannesburg, South Africa. Close ). In the Paradise Shelduck (Tadorna variegata) of New Zealand, adult females also have striking white heads and the juveniles resemble adult males as in the South African Shelduck (4 Marchant, S., and P. J. Higgins, Editors (1990). Handbook of Australian, New Zealand & Antarctic Birds. Volume 1: Ratites to Ducks. Oxford University Press, Melbourne, Australia. Close ) - none of the other Tadorna species show this pattern (5 Madge, S., and H. Burn (1988). Waterfowl: An Identification Guide to the Ducks, Geese and Swans of the World. Houghton Mifflin Company, Boston, Massachusetts, USA. Close , 6 Kear, J., Editor (2005). Ducks, Geese and Swans. Oxford University Press, Oxford, UK. Close ). The sexes of juveniles can be differentiated as early as at 49 days (i.e., well before fledging) on the basis of the white rims around the eyes and bill of females; these regions are uniformly gray in juvenile males (7 Siegfried, W. R. (1966). On the post-embryonic development of the South African Shelduck Tadorna cana (Gmel.). Ostrich 37:149–151. Close ).

Formative Plumage

Similar to Definitive Basic Plumage in each sex except some scattered juvenile body feathers (especially among lower back, rump, and lower underparts) can be retained, brownish and more worn than replaced formative feathers. Juvenile remiges retained, the outer primaries browner, more pointed, and relatively worn compared to basic feathers. Some juvenile outer greater coverts are also often retained, narrow, rounded, brown, and contrasting with the squarer whiter formative coverts. Replaced formative coverts may also be washed brown, although this appears to be the case in some definitive basic feathers as well; study needed. Some outer rectrices may also occasionally be retained, narrow, brownish and notched. The head and breast of males can become bleached to buff and buffy whitish in worn plumage.

First and Definitive Alternate Plumages

Often referred to as "eclipse" plumages. Study is needed on the existence and extent of Prealternate Molts in this species (see Molts). Males may obtain paler and buffier heads post-breeding that may result from Prealternate Molts, or it could result from bleaching and wear; study needed. Otherwise, examination of Macaulay Library images indicates little or no molt or change in body-feather appearance during this period in either sex, except for the effects of wear.

Definitive Basic Plumage

Female

Females are more striking in appearance than males due to their white head pattern, which is unusual among Anatidae. In Tadorna, only the Paradise Shelduck shows stronger reverse plumage dimorphism (5 Madge, S., and H. Burn (1988). Waterfowl: An Identification Guide to the Ducks, Geese and Swans of the World. Houghton Mifflin Company, Boston, Massachusetts, USA. Close , 6 Kear, J., Editor (2005). Ducks, Geese and Swans. Oxford University Press, Oxford, UK. Close ). The hindcrown, neck, and lower throat are dark brown, contrasting with the white forehead, malar region, chin, upper throat, and through the eye, variably to include the upper sides of head to the entire sides of the head; lower auriculars can be brown, white, or white with brown feathers and often show a small rounded brown spot. The remainder of the body feathering is primarily russet. The tail, uppertail coverts, rump, and lower back are black, and this black feathering extends to the sides of the rump. The upperwing secondary coverts are primarily to entirely white and the primaries, upperwing primary coverts, and alula are black. Some proximal upperwing coverts can be washed pale brown, apparently plumage coloration and not staining. The secondaries are strongly tinged glossy green above, sometimes resulting in a green patch on the folded wing, and show white tips when fresh. The underwing secondary coverts and axillaries are white, and those of the greater primary coverts are basally white with increasingly broad black tips towards the outer wing.

It has been suggested that the white face patch in females increases in size with age (7 Siegfried, W. R. (1966). On the post-embryonic development of the South African Shelduck Tadorna cana (Gmel.). Ostrich 37:149–151. Close ), but this has been questioned based on data from captive birds (8 van Ee, C. A. (1971). Variations in the head pattern of the female South African Shelduck. Ostrich 42:149–150. Close ). Four different head patterns have been identified (8 van Ee, C. A. (1971). Variations in the head pattern of the female South African Shelduck. Ostrich 42:149–150. Close ). Usually, only the facial area is white, but in a small minority of individuals (ca. 0.35%) most, or even all (about 0.08%), of the head, upper neck, and throat are white. This categorization was subsequently expanded to recognize 12 different head patterns, with extensions to the white area falling into two main groups: either from behind the eye downwards, or downwards on the throat (9 Geldenhuys, J. N. (1983). Morphological variation in wing-moulting South African Shelducks. Ostrich 54(1):19–25. Close ). In some cases, extensions in both directions are present, but females with small extensions to the white face patch predominate, whilst those with mainly white heads were scarce. There is no seasonal change in the facial pattern.

Definitive Basic Plumage in both sexes is distinguished from Formative Plumage by body feathering uniform in wear, without mixed generations; upperwing coverts uniform in wear, the feathers broad and white to predominantly white; primaries and secondaries longer, darker, glossier, and fresher; tail with uniformly broad and black rectrices.

Male

The male is similar to the Definitive Basic female but the head and upper neck are uniformly plain gray and the nape and breast are paler tan creating a broad collar. An indistinct white partial eye ring can be present, and the lower porting of the gray can darken forming an indistinct gray ring around the lower neck. The head and breast can become bleached with wear, acquiring a bright creamy hue (10 Geldenhuys, J. N. (1981). Moults and moult localities of the South African Shelduck. Ostrich 52(3):129–134. Close ), but whether an alternate plumage following molt also exists requires further study (see Molts).

Aberrant Plumages

An instance of leucism or albinism has been recorded, with the bird described as "uniformly coloured pale creamy-white" (11 Siegfried, R. (1966). Albinistic Shelduck. Promerops 80:4–5. Close ).

General

Molt and plumage terminology follows Humphrey and Parkes (12 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. (13 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 ) and Pyle (14 Pyle, P. (2005). Molts and plumages of ducks (Anatinae). Waterbirds 28(2):208–219. Close , 15 Pyle, P. (2013). Molt homologies in ducks and other birds: A response to Hawkins (2011) and further thoughts on molt terminology in ducks. Waterbirds 36(1):77–81. 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 breeding season, location, or time of the year, the latter generally referred to as “life-cycle” molt terminology (16 Jenni, L., and R. Winkler (2020). Moult and Ageing of European Passerines. Second edition. Bloomsbury, London, UK. Close ; see also 17 Pyle, P. (2022). Defining moults in migratory birds: a sequence-based approach. Journal of Avian Biology 2022(5):e02958. Close , 18 Kiat, Y. (2022). Moult terminology: Let’s make it simpler! Ibis 165(2):697-703 Close ). In north-temperate latitudes, the Humphrey-Parkes (H-P) and life-cycle nomenclatures correspond to some extent but terms are not synonyms due to the differing bases of definition. Prebasic molts often correspond to “post-breeding“ or “post-nuptial“ molts, preformative molts often correspond to “post-juvenile“ molts, and prealternate molts often correspond with “pre-breeding“ molts of life-cycle terminology. The terms prejuvenile molt and juvenile plumage are preserved under H-P terminology (considered synonyms of first prebasic molt and first basic plumage, respectively) and the former terms do correspond with those in life-cycle terminology. The molts and plumages of ducks have recently been revised based on the perceived evolution of molt strategies from geese, such that what is usually considered the pre-breeding molts in life-cycle terminology (molt of wings followed by a complete molt of body feathers following breeding), in summer and fall, is now considered the prebasic molts, and the post-breeding molts in life-cycle terminology (partial molts of some to most body feathers and some tertials and rectrices into "eclipse" plumage to provide crypsis for breeding in females and flightless period in both sexes), in spring and summer, is now considered the prealternate molts (14 Pyle, P. (2005). Molts and plumages of ducks (Anatinae). Waterbirds 28(2):208–219. Close , 19 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, California, USA. Close , 15 Pyle, P. (2013). Molt homologies in ducks and other birds: A response to Hawkins (2011) and further thoughts on molt terminology in ducks. Waterbirds 36(1):77–81. Close ).

South African Shelduck exhibits either a Complex Basic or a Complex Alternate molting strategy (cf. 13 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 , 20 Howell, S. N. G. (2010). Peterson Reference Guide to Molt in North American Birds. Houghton Mifflin Harcourt, Boston, Massachusetts, USA. Close ). It includes complete prebasic molts and a partial preformative molt, and may also include limited prealternate molts in both first and definitive cycles; study needed (see below).

Prejuvenile Molt

Occurs primarily August–September. Complete, at or near the natal site. Following hatching, the first contour feathers appear at ca. 18 days in the flanks and tail in captive chicks (7 Siegfried, W. R. (1966). On the post-embryonic development of the South African Shelduck Tadorna cana (Gmel.). Ostrich 37:149–151. Close ). At 28 days the chicks were still mainly downy, but feathers were present on the breast, flank, abdomen and scapulars, and the remiges were just emerging. By 35 days the upperwing coverts had appeared, the tail, breast, flanks and abdomen were well feathered, and the first feathers were appearing on the back, neck, crown and forehead, but the rest of the head was downy. At 42 days the breast, flanks, abdomen, and certain parts of the head and neck had mature feathers. At 49 days down-tipped feathers were present on the nape. At 56 days the chicks were almost completely feathered, including on the wings, but the nape feathers were still tipped with down, and the back and rump feathers were not fully developed. Growth was virtually complete by 63 days.

The sexes of captive chicks can be differentiated as early as 49 days (i.e., well before fledging) based on white rims around the eyes and bill of females; these regions are uniformly gray in young males, which in addition had paler-colored breasts (7 Siegfried, W. R. (1966). On the post-embryonic development of the South African Shelduck Tadorna cana (Gmel.). Ostrich 37:149–151. Close ).

Preformative Molt

Occurs primarily September-November. Birds undergoing the preformative molt largely avoid aggregations of birds undergoing definitive prebasic molt (9 Geldenhuys, J. N. (1983). Morphological variation in wing-moulting South African Shelducks. Ostrich 54(1):19–25. Close ). Includes most body feathers, often 2–3 tertials, usually all rectrices, and some to most (perhaps occasionally all?) proximal upperwing secondary coverts, but no primaries, primary coverts, or secondaries other than the tertials. The larger scapulars, wing coverts, and rectrices are often molted last, as late as December on winter grounds. Some juvenile body feathers may be retained, especially in the lower back, rump, and lower underparts. Between 49 and 77 days of age, the white rims of females expanded, by ca. 90 days had merged to form the white face patch of the adult female, and continued to expand subsequently (7 Siegfried, W. R. (1966). On the post-embryonic development of the South African Shelduck Tadorna cana (Gmel.). Ostrich 37:149–151. Close ).

First and Definitive Prealternate Molts

These molts have not been confirmed but occur or have been reported in other species of Tadorna of seasonal climates (21 Cramp, S., and K. E. L. Simmons, Editors (1977). The Birds of the Western Palearctic. Volume 1. Ostrich to Ducks. Oxford University Press, Oxford, UK. Close , 4 Marchant, S., and P. J. Higgins, Editors (1990). Handbook of Australian, New Zealand & Antarctic Birds. Volume 1: Ratites to Ducks. Oxford University Press, Melbourne, Australia. Close ) and so might be expected in South African Shelduck, as reported (10 Geldenhuys, J. N. (1981). Moults and moult localities of the South African Shelduck. Ostrich 52(3):129–134. Close ). If present, occurs primarily in August–October and may include the head feathers but appears to include few other feathers based on examination of Macaulay images. Geldenhuys (10 Geldenhuys, J. N. (1981). Moults and moult localities of the South African Shelduck. Ostrich 52(3):129–134. Close ) also found that possibly two rectrix molts occur per cycle but confirmation is needed. The heads of males become paler during the post-breeding period, but study is needed on how much this is caused by molt vs. feather bleaching and wear (see images under Plumages).

Definitive Prebasic Molt

Occurs primarily in October-March, with flight feathers replaced prior to body feathers, as in other waterfowl (14 Pyle, P. (2005). Molts and plumages of ducks (Anatinae). Waterbirds 28(2):208–219. Close ). Throughout the range, the remiges are replaced during a relatively narrow midsummer window (late October to late February, mainly November‒January), when birds congregate at large, permanent freshwater bodies, apparently preferring sites undisturbed by man (22 Taylor, J. S. (1944). Notes on the South African Shelduck. Ostrich 15:188–193. Close , 2 Shewell, A. L. (1959). The waterfowl of Barberspan. Ostrich Supplement 3:160–179. Close , 23 Dean, W. R. J. (1978). Molt seasons of some Anatidae in the Western Transval. Ostrich 49(2):76–84. Close , 10 Geldenhuys, J. N. (1981). Moults and moult localities of the South African Shelduck. Ostrich 52(3):129–134. Close , 9 Geldenhuys, J. N. (1983). Morphological variation in wing-moulting South African Shelducks. Ostrich 54(1):19–25. Close , 24 Ndlovu, M., P. A. R. Hockey, and G. S. Cumming (2017). Geographic variation in factors that influence timing of moult and breeding in waterfowl. Zoology 122:100–106. Close ). The largest recorded flocks occur at these molting localities, where concentrations of up to ca. 5,000 birds have been noted (25 Brown, L. H., E. K. Urban, and K. Newman (1982). The Birds of Africa. Volume 1. Academic Press, London, UK. Close ). This midsummer molting period is unusual. Other common southern African waterfowl, e.g., Spur-winged Goose (Plectropterus gambensis) , Egyptian Goose (Alopochen aegyptiaca) , Yellow-billed Duck (Anas undulata) and Anas erythrorhyncha, typically molt during midwinter (24 Ndlovu, M., P. A. R. Hockey, and G. S. Cumming (2017). Geographic variation in factors that influence timing of moult and breeding in waterfowl. Zoology 122:100–106. Close ). Midsummer molting corresponds with the peak rainfall season throughout most of the species’ distribution. At one major molting locality (Barberspan) the number of molting shelducks was positively correlated with rainfall. However, in the Western Cape Province winter-rainfall region, this species still molts in midsummer when rainfall is low. Molting during the dry season in the Western Cape may reflect the relatively recent colonization of this area, where the species has not yet had time to adjust its annual cycle to correspond with the local rainfall regime.

All of the remiges are shed within one to six days, starting with the primaries (2 Shewell, A. L. (1959). The waterfowl of Barberspan. Ostrich Supplement 3:160–179. Close , 23 Dean, W. R. J. (1978). Molt seasons of some Anatidae in the Western Transval. Ostrich 49(2):76–84. Close ). A few days later the primary and secondary coverts are molted. The flightless period spans ca. 28–40 days, including 3–6 days prior to the remiges being shed, and the flight feathers take approximately three days to harden. There is an apparent increase in body mass immediately prior to molt, unlike in several other southern African waterfowl (26 Ndlovu, M. (2012). Environmental influences on moult and movement strategies in southern African waterfowl. Ph.D. thesis, University of Cape Town, Cape Town, South Africa. Close ), followed by a loss in weight of ca. 25%–35%, proportionately slightly greater in females than in males (mean 28% versus 26%), during the wing-molting period (2 Shewell, A. L. (1959). The waterfowl of Barberspan. Ostrich Supplement 3:160–179. Close , 9 Geldenhuys, J. N. (1983). Morphological variation in wing-moulting South African Shelducks. Ostrich 54(1):19–25. Close ). Body mass and pectoral muscle size decrease after the onset of molt, stabilize when the flight feathers are about two-thirds grown, and subsequently increase until molt is completed (27 Ndlovu, M., G. S. Cumming, and P. A. R. Hockey (2017). Body mass and pectoral muscle size changes in African waterfowl during moult. African Journal of Wildlife Research 47(1):24–31. Close ). This pattern is similar to that in Spur-winged Goose and Egyptian Goose, but differs from that of Yellow-billed Duck, Red-billed Duck, and Southern Pochard (Netta erythrophthalma). It appears likely that the reduced body mass recorded during the early molting period facilitates some flight on partially grown remiges later in the cycle, thereby permitting resumption of feeding as soon as possible.

Molting birds spend the day in deep water and only approach shallow water and shorelines at night to feed (2 Shewell, A. L. (1959). The waterfowl of Barberspan. Ostrich Supplement 3:160–179. Close ). It has been suggested that flightless birds apparently take little food (28 Geldenhuys, J. N. (1977). Feeding habits of South African Shelducks. South African Journal of Wildlife Research 7:5–9. Close ) but this has been questioned (26 Ndlovu, M. (2012). Environmental influences on moult and movement strategies in southern African waterfowl. Ph.D. thesis, University of Cape Town, Cape Town, South Africa. Close ). Flightless birds swim low in the water, are secretive, dive readily, and sometimes hide in emergent vegetation (23 Dean, W. R. J. (1978). Molt seasons of some Anatidae in the Western Transval. Ostrich 49(2):76–84. Close ). Molt of rectrices is gradual and usually occurs about one month after wing molt is completed (2 Shewell, A. L. (1959). The waterfowl of Barberspan. Ostrich Supplement 3:160–179. Close ).

Bill

Black in adults. The bills of hatchlings can be grayish washed pink, becoming grayish as juveniles.

Iris and Facial Skin

Iris is dark brown at all ages.

Tarsi and Toes

In adults, the tarsi are black. Females usually (80%) have dark gray feet blotched variably with light pink on the inner sides of the toes; the remainder have uniformly black feet as in males (9 Geldenhuys, J. N. (1983). Morphological variation in wing-moulting South African Shelducks. Ostrich 54(1):19–25. Close ). The tarsi of hatchlings may be grayish washed pink, becoming grayish as juveniles.

Linear Measurements

Overall length 61‒64 cm (29 Allan, D. G. (2005). South African Shelduck Tadorna cana. In Roberts Birds of Southern Africa. Seventh Edition. (P. A. R. Hockey, W. R. J. Dean, and P. G. Ryan, Editors), The Trustees of the John Voelcker Bird Book Fund, Cape Town. pp. 93–95. Close ). Males larger than females.

Linear measurements, in mm (30 South African Bird Ringing Unit (SAFRING), University of Cape Town (2021). Unpublished data. Close ):

Mass

Males are heavier than females. Males: 900–2,150 g (mean 1,452 g, SD = 208.9 g, n = 277 confirmed adult males only with 90% of records from Nov.–Dec. when captured at molting localities mainly in the Free State and North-West provinces) (30 South African Bird Ringing Unit (SAFRING), University of Cape Town (2021). Unpublished data. Close ), 910–2,200 g (mean 1,357 g, n = 1,171; 31 Maclean, G. L. (1993). Roberts’ Birds of Southern Africa. Sixth edition. John Voelcker Bird Book Fund and New Holland, Cape Town, South Africa. Close ), 1,032–2,032 g (mean 1,527 g, n = 171) (Barberspan; 32 Dean, W. R. J., and D. M. Skead (1979). The weights of some southern African Anatidae. Wildfowl 30:114–117. Close ), mean 1,758 g (n = 152) (Barberspan; 2 Shewell, A. L. (1959). The waterfowl of Barberspan. Ostrich Supplement 3:160–179. Close ), 1,012–1,295 g (mean 1,187 g, n = 5) (Free State Province; 33 Herholdt, J. J. (1988). Bird weights from the Orange Free State (Part 1: nonpasserines). Safring News 17:3–14. Close ). Females: 800–1,665 g (mean 1,197 g, SD = 187.4 g, n = 235 confirmed adult females only with 87% of records from Nov.–Dec. when captured at molting localities mainly in the Free State and North-West provinces) (30 South African Bird Ringing Unit (SAFRING), University of Cape Town (2021). Unpublished data. Close ), 700–1,835 g (mean 1,115 g, n = 1,092) (31 Maclean, G. L. (1993). Roberts’ Birds of Southern Africa. Sixth edition. John Voelcker Bird Book Fund and New Holland, Cape Town, South Africa. Close ), 872–1,835 g (mean 1,229 g, n = 215) (Barberspan; 32 Dean, W. R. J., and D. M. Skead (1979). The weights of some southern African Anatidae. Wildfowl 30:114–117. Close ), mean 1,417 g (n = 222) (Barberspan; 2 Shewell, A. L. (1959). The waterfowl of Barberspan. Ostrich Supplement 3:160–179. Close ), 1,049–1,240 g (mean 1,173 g, n = 3) (Free State; 33 Herholdt, J. J. (1988). Bird weights from the Orange Free State (Part 1: nonpasserines). Safring News 17:3–14. Close ). The radical variation in both males and females is largely due to extensive weight loss during the wing-molting period (9 Geldenhuys, J. N. (1983). Morphological variation in wing-moulting South African Shelducks. Ostrich 54(1):19–25. Close ).