South African Shelduck Tadorna cana Scientific name definitions

David G. Allan
Version: 2.0 — Published February 23, 2023

Demography and Populations


During the breeding season, large flocks of non-breeding birds can still be observed, mainly comprising pairs (109, 1), although it has also been alleged that such flocks comprise chiefly females (22). In Free State Province the pre-breeding period (early winter) is characterized by the population being split into sedentary territorial pairs, nomadic non-territorial pairs, and flocks of non-breeders (1). Territorial adults comprised 69.0% of birds at one site and 74.4% at another during this time, relative to the total adult population. Sightings of solitary individuals usually (90%) involved females.

Measures of Breeding Activity

Age at First Breeding

No information (29).

Annual and Lifetime Reproductive Success

At Graaff-Reinet, Eastern Cape Province, up to 13 chicks were seen in a brood, with a mean brood size of 7.6 (n = 15) (22). In Free State Province, mean brood size decreased from a mean 7.4 for one-week-old broods to 5.8 for broods at fledging (70 days) (n = 139 broods monitored), i.e., a loss of 1.6 ducklings per brood across the fledging period, excluding seven broods that were entirely lost (5%), six when 7–14 days old, and one when 14–21 days old (1). The largest broods had the lowest rate of chick loss. Brood sizes ranged between one and 21 chicks (129). There is one record of a pair with 28 downy young all of the same size but it is suggested that some pairs may ‘kidnap’ the young of others (130).

Breeding success was high in Free State Province, and of 139 broods which safely arrived at water from their breeding burrows, only seven were entirely lost before fledging (1). Of the remainder, attrition pre-fledging accounted for only an average of 1.6 chicks per brood, i.e., a reduction in mean brood size from 7.4 to 5.8. Most mortality occurred in the first four weeks. Survival to fledging was slightly, but significantly, higher in a Karoo study (76.4%) compared to a grassland study area (71.5%), due to higher mortality during the first two weeks in the latter region. Examining all territorial pairs, the mean number of young successfully reared to fledging per annum was 5.0, with 86% of all pairs breeding successfully. High breeding success was attributed to the strongly developed pair bond, territoriality, and social hierarchy among age classes. Late broods were no less successful than early broods, but pairs that established territories earliest (but did not necessarily lay immediately) had larger brood sizes, and suffered lower rates of chick loss, than pairs establishing territories later in the highly circumscribed breeding season.

Birds captured for ringing at Barberspan comprised only 4% juveniles of the year in the post-breeding period (n = 390), but this figure is unlikely to be representative of breeding success as this site is apparently distant from the main breeding areas, and most juveniles avoid wing-molting grounds, instead apparently remaining close to their natal sites during their first year (2). At Vogelvlei 23% of birds captured during the post-breeding period were juveniles (n = 209) and little wing-molting occurs at this site (102). The high density of breeding pairs present in the wetter eastern parts of the range suggest that this region is a particularly important breeding ground, relative to the drier west (1).

Number of Broods Normally Reared per Season

Apparently single-brooded, but may replace failed clutches or broods lost when chicks are small (22, 103).

Life Span and Survivorship

Adult populations remain relatively stable, despite wide annual variations in habitat availability. Viewed in the light of the species’ high breeding productivity, this suggests that full-grown birds suffer high mortality rates (1). From ringing information, the longevity record is 13 years 11 months, with five additional records exceeding ten years (99). One captive bird lived for more than 40 years (131).

Disease and Body Parasites

Susceptible to botulism (Clostridium botulinum, type C) and at two sites 18–19% mortality was registered during outbreaks (132, 133). Captive birds are prone to tuberculosis, aspergillosis, and amidostomiasis (gizzard worm) (134). One bird probably died from avian cholera (Pasteurella multoceda) at Jutten Island in Saldanha Bay, Western Cape Province, in October 1991 (135). Avian influenza virus was isolated from the gut and organs of one of eight birds sampled at Oudtshoorn, Western Cape (136). Avian influenza virus was also identified in two additional individuals (H5 and H6 strains) (137). It is considered a fairly high-risk species for the transmission of avian influenza (138).

Causes of Mortality

Information needed.

Population Spatial Metrics

Territory Size

Territory sizes comprise 75–170 m of shoreline and a distance inward to the center of wetlands of 50–80 m, i.e., about 0.5 ha of water (n = 24) (1). At larger wetlands several territories may abut one another.

Population Status


In some parts of its range, South African Shelduck can be the most abundant waterfowl species, e.g., in southern and western Free State Province (98), and overall at large irrigation dams throughout the Free State it was the second-most common of 15 waterfowl species, after the Egyptian Goose (Alopochen aegyptiaca) (97, 98). The total population is estimated at about 50,000 (Wetlands International 2021).

At 23 known molt localities in South Africa, mainly large dams, 16 of which were in the Free State, 30,000 individuals were estimated to occur in the 1980s, or at least 70% of the South African population, the country in which the vast majority of the global population occurs (10). The six largest dams (Vaal, Bloemhof, Allemanskraal, Erfenis, Krugersdrift, and Kalkfontein) supported 78% of these birds. There are two additional major molting localities in Western Cape Province (Radyn Dam and De Hoop Vlei, the latter a natural wetland) (93). The largest flocks are present at these molting localities, with up to about 5,000 birds (25). Recent (April 2021) data from the biannual South African Coordinated Waterbird Counts Project (CWAC 2021) lists 20 sites in Free State, six in Western Cape and two in Northern Cape Province, as having recorded maximum numbers exceeding the Ramsar threshold of 500 individuals for this species (mean and maximum numbers in brackets): Free State: Allemanskraal Dam (76; 611), Bloemhof Dam (200; 2,854), Danielskuil Pan (265; 2,762), Deelpan (616; 6,447), Donkerpoort Farm Dam 1 (108; 611), Erfenis Dam (141; 1,344), Gariep Dam (270; 840), Kalkfontin Dam (504; 2,721), Knellpoort Dam (42; 644), Krugersdrift Dam (483; 3,545), Leeupan (239; 879), Vaalbank Dam (417; 3,263); Western Cape: De Hoop Vlei (84; 730), Koenskraal Pan (295; 675), Radyn Dam (334; 1,750), Verlorenvlei (132; 501), Voelvlei (461; 1,490), Wadrif Saltpan (98; 1,365); Northern Cape: Orange River Mouth (180; 678) and Spitskop Dam (534; 2,926). The total mean number of birds recorded at these 28 sites is 5,479 individuals, or 46% of the total mean number recorded at all 371 wetlands covered by this project. Biannual counts such as these, however, can overlook large temporary influxes , e.g., a temporary influx of 1,412 molting birds to De Hoop Vlei in 2015 (139). The population inhabiting the former Transvaal Province (northeast South Africa) was estimated at ca. 5,000 birds in the mid-1980s (126). It is estimated that 15% of the global population occurs in Namibia (140). Up to ca. 90 birds have been counted at regular sites in southeastern Botswana, and the total population in this region is estimated at about 200–300 birds (49). The two most regular sites in Lesotho — Letšeng-la-Letsie and Tša-Kholo — support up to about 30 individuals each, and the total Lesotho population is thought not to exceed 100 birds (51).


The South African Shelduck has undoubtedly increased in abundance both within its ancestral range and by expansion into new regions (see under Historical Changes to the Distribution and under Conservation Status).

Recommended Citation

Allan, D. G. (2023). South African Shelduck (Tadorna cana), version 2.0. In Birds of the World (G. D. Engelbrecht, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.soashe1.02