Species names in all available languages
|English||South African Shelduck|
|English (United States)||South African Shelduck|
|French||Tadorne à tête grise|
|French (French Guiana)||Tadorne à tête grise|
|Lithuanian||Pilkagalvė urvinė antis|
|Spanish (Spain)||Tarro sudafricano|
|Turkish||Gri Başlı Angıt|
This account is part of the 8th edition of Roberts Birds of Southern Africa. This project is a joint collaboration between the John Voelcker Bird Book Fund and the Cornell Lab of Ornithology. David G. Allan revised the account. Peter Pyle contributed to the Plumages, Molts, and Structure page. Peter F. D. Boesman contributed to the Sounds and Vocal Behaviors page. Arnau Bonan Barfull curated the media. Huy C. Truong revised the distribution map. Qwahn Kent copyedited the account. Guy M. Kirwan reviewed the account.
Tadorna cana ("Gmelin, JF", 1789)
The Key to Scientific Names
South African Shelduck Tadorna cana Scientific name definitions
Version: 2.0 — Published February 23, 2023
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The South African Shelduck breeds in isolated pairs, usually well separated from other pairs, probably at least partly due to their specialized nesting requirements.
Breeding has been recorded from as far north as ca. 20˚S in Namibia and as far east as 30˚E in KwaZulu-Natal (115), although breeding even further east, at ca. 29˚50’S, 30˚32’E, near Durban, has been noted (DGA personal observation).
The breeding period is highly circumscribed, unlike in the Egyptian Goose (Alopochen aegyptiaca). A comprehensive analysis of seasonality from throughout the range, comprising 681 georeferenced records, shows that hatching dates are highly synchronous with a marked September peak, and the vast majority of records are in July‒November (although hatching dates apparently cover all months) (115). Nesting is consistently in the drier months, i.e., when rainfall is below the annual average. Breeding seasonality in southern Africa is similar to that exhibited by the Egyptian Goose and African Black Duck (Anas sparsa), and is unusual compared to most other southern African waterfowl that breed during the summer, i.e., the period of highest rainfall throughout most of the region (115, 24). Egg-laying (as opposed to hatching) data from across the range confirm early winter to early summer breeding (29).
In Eastern Cape Province, courtship begins in February and continues until May, by June most pairs are firmly established, egg-laying occurs July–October, newly hatched young are observed August–November (mainly September–October), and full-grown young are seen with their parents from October until December (22, 116). In Free State Province, egg-laying occurs during a relatively short period that is consistent between years, even when rainfall varies widely (103). The earliest laying date was about 17 May and the latest about 25 September, i.e., spanning 18 weeks, peaking during the last week of July. A comparison of breeding seasonality between Northern, Eastern, and Western Cape provinces found little difference between these regions, with peak activity (largely based on observations of chicks) reported July–October in all three areas (117). Atlas data (again based largely on sightings of young) from throughout the species’ range show main breeding during July–November (peak August–October), but with a clear indication of earliest breeding, by about two months, in the north of the range (peak August) compared to the south (peak October) (43).
Nesting occurs during the dry (midwinter) period, explaining why breeding is largely restricted to permanent, and not seasonal, wetlands (103). Chicks feed largely on submerged aquatic plants in shallow water and such conditions are optimal during the dry winter period, explaining the timing of breeding. Nesting during the dry season may also be related to the species’ subterranean nests, which may be prone to flooding (118, 24). In addition, there is scant littoral vegetation at this time of year, aiding in predator detection. Breeding in the winter-rainfall Western Cape Province may be later than in other parts of the range, although still overlapping the wet period and apparently as part of a broader latitudinal trend, rather than a specific dichotomy between the summer- and winter-rainfall regions. Breeding during the wet season in Western Cape may reflect the relatively recent colonization of this area and that the species has not yet adjusted its breeding (and molt) to correspond with the rainfall regime (24).
Females lead the pair in prospecting for nest sites, and males are largely responsible for defending the area from other pairs (1).
Nests are located in holes in the ground, especially those of aardvark (Orycteropus afer) (1, 119). Of 14 nests, 11 were in aardvark burrows and three were in smaller excavations, either of springhares (Pedetes capensis) or porcupines (Hystrix africaeaustralis) (1). Another nest was situated ca. 9 m down an aardvark burrow (120). The species also apparently nests occasionally among rocks (66), once in haystack (119), and sometimes in anthropogenic ducts and culverts (3).
This unusual choice of typical nest site is probably related to the nature of the xeric vegetation at and around the wetlands this species inhabits, i.e., the absence of secure breeding sites in the form of dense wetland vegetation or tall trees (91). Underground nesting has also been related to an intolerance of high temperatures in the species (44) but this requires confirmation (115). Heavy rainfall may flood and collapse breeding burrows, resulting in the birds being precluded from nesting and prematurely concentrating at the large waterbodies usually only frequented during the post-breeding period (118, 24). The choice of nest site may therefore be implicated in the species’ largely xeric distribution. It is unclear if the choice of nest site is more or less hazardous (to the incubating female and the eggs) than more typical waterfowl nesting situations (109).
Nests are sited up to 2.0 km from the territorial waters (1, 119).
Structure and Composition
Eggs are laid in a bowl of grass and down feathers constructed by the female (119). In three nests under captive conditions, both contour (9–71 feathers) and down (61–940 feathers) feathers were used (121). One nest under natural conditions apparently included a large dry thistle weed (120).
Maintenance or Reuse of Nests
64.5–72.0 × 48–52 mm (mean 68.7 × 50.3 mm, n = 13) (122, Ditsong Museum of Natural History collection).
74.5–99.5 g (mean 89.0 g, n = 50) (31).
Color and Surface Texture
Unmarked pure white or cream-colored with a matt surface (22, 31).
All apparently confirmed complete clutches (n = 26) comprised 4–11 eggs (120, 123, 124, 125, Ditsong Museum of Natural History collection), except for one record of 15 eggs (35). There are three apparently confirmed records of complete four-egg clutches. The mean and modal clutch sizes are 7.4 and 7.0 eggs, respectively.
The egg-laying period is highly circumscribed (115). Egg-laying data from across the range confirm early winter to early summer breeding, with a marked peak in late winter, in July–August (68%), the vast majority in June–September (86%), and all records are during March–December (n = 115) (29).
In Free State Province, the earliest laying date was about 17 May and the latest about 25 September, i.e., spanning 18 weeks, peaking during the last week of July, and 90% of clutches were started during the seven-week period 20 June–17 August (n = 171) (103). Other precise egg-laying dates for specific regions include:
- Namibia: April (n = 1), May (n = 2), June (n = 5), July (n = 3), August (n = 2), September (n = 1) (125).
- Botswana: May (n = 1), June (n = 3), July (n = 5), August (n = 2), September (n = 1), September/October (n = 1), November (n = 1), December/January (n = 1) (49).
- South Africa: Former Transvaal Province (northeastern South Africa): April (n = 1), May (n = 1), June (n = 1), July (n = 3), August (n = 8) (126).
- South Africa: Western Cape Province: August (n = 1), September (n = 4) and October (n = 1) (45).
This regional egg-laying information tends to confirm earlier laying in the north, although sample sizes are small and coverage uneven.
The incubation period and the interval between the laying of eggs is unknown, but has been assumed to be about 30 days and one day, respectively (103). Incubation probably only commences when the clutch is complete or close to completion, such that the young hatch fairly close together and can be taken simultaneously to water.
Incubation is solely by the female (109). Males seem to spend most of the incubation period close to the nesting burrow and away from the aquatic breeding territory, and apparently warn the female of potential predators by loud hissing (1, 127). The female leaves the nest once or twice a day, joining the male to feed (119).
Condition at Hatching
Captive day-old chicks weighed 45.2–57.2 g (mean 52.8 g, n = 7) (128), or 52.0–61.5 g (mean 56.5, n = 9) (25). A five-day-old captive chick weighed 60 g and had mainly dusky brown upperparts, broken by white blotches, and its underparts were white (7). The wing had a white bar and there were elongated white blotches on the sides of the back immediately behind the base of the wings. There were also two large white patches on the rump near the base of the tail. The cheeks and sides of the neck were white, continuing without interruption to the chin, throat and breast, and over the abdomen to the tail. The maxilla was blackish gray, tipped pale gray, and the mandible was blackish gray tinged olive and tipped pink. The iris was dusky brown, the legs and feet buffy brown, and the membranes and toes blackish gray. The chick resembled that of the Egyptian Goose (Alopochen aegyptiaca), except that it lacked the white supercilium of the latter species. It also differed in the darker color of its soft parts, and the white blotches on the lower rump and wing were larger, as was the ‘egg-tooth’.
Growth and Development
The first contour feathers appear at ca. 18 days in the flanks and tail in captive chicks (7). 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 wing-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. At 42 days the head and neck had gray feathers (as in the adult male) and contrasted distinctly with the tawny-orange lower neck and breast. At 49 days female chicks had narrow white rims around the eyes and base of the bill, whereas these regions were uniformly gray in males, which in addition had paler-colored breasts. Between 49 and 77 days 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. While flightless, wild chicks dive to escape predators (22). Flight is possible at ca. 70 days in captive chicks (7) and wild chicks take approximately 60–75 days to achieve adult size and flight capabilities (22). Families apparently separate when the young are about 90–120 days old (92).
Both members of a pair lead the chicks to water, usually in the early morning (1). Both sexes also subsequently care for the young, which are kept in muddy areas with shallow water, unless disturbed when family parties take refuge in deeper water (22). Both pair members vigorously chase large birds, e.g., herons and cormorants, away from their chicks.
Brood Parasitism by Other Species
Brood parasitism by other waterfowl species has not been recorded.