Behavior

Many aspects of the basic behavior of this species are poorly known.

Information needed.

Information needed.

Territorial Behavior

Intra-sexual fighting (chasing and pecking) has been noted for both sexes, and breeding pairs noisily drive off intruding pairs and individuals, with the female often taking the lead in such encounters (22 Taylor, J. S. (1944). Notes on the South African Shelduck. Ostrich 15:188–193. Close , 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 ). During the incubation and chick-rearing periods, however, territorial defense is largely the preserve of the male (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 ). Mated females appear particularly intolerant of same-sex intruders (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 ) and females in mated pairs within flocks can even be intolerant of other unpaired females in close proximity (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 ). The skewed sex ratio in favor of females may be responsible for both their active role in courtship (109 Siegfried, W. R. (1976). Sex ratio in the Cape Shelduck. Ostrich 47:113–116. Close ) and their intense intra-sexual aggression.

Mating System and Operational Sex Ratio

Monogamous, and pair bonds are probably long-lasting or permanent (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 ).

Despite being monogamous (109 Siegfried, W. R. (1976). Sex ratio in the Cape Shelduck. Ostrich 47:113–116. Close ), information from large waterbodies shows that males are usually outnumbered substantially by females, i.e., 1.0:4.2 and 1.0:4.1, based on counts at two sites in Eastern Cape Province (22 Taylor, J. S. (1944). Notes on the South African Shelduck. Ostrich 15:188–193. Close ), 1.0:1.3 based on ringed birds (n = 209) and counts at Vogelvlei (102 Siegfried, W. R. (1967). Trapping and ringing of Egyptian Geese and African Shelduck at Vogelvlei, Cape. Ostrich 38:173‒178. Close ), 1:2 based on counts in the Goldfields area, Free State Province, (n = 4,224) (8 van Ee, C. A. (1971). Variations in the head pattern of the female South African Shelduck. Ostrich 42:149–150. Close ), 1:1.2 in southern Free State (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 ), and 1.0:1.5 based on ringed birds at Barberspan (n = 375) (2 Shewell, A. L. (1959). The waterfowl of Barberspan. Ostrich Supplement 3:160–179. Close ). Recent counts at Barberspan (North-West Province) and Strandfontein (Western Cape Province) found a lower bias (1.0:1.1) (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 ). At one site (Bloemfontein sewage works, Free State) a sex ratio of 2:1 in favor of males was recorded based on counts (n = 3,019) (8 van Ee, C. A. (1971). Variations in the head pattern of the female South African Shelduck. Ostrich 42:149–150. Close ).

A detailed review of sex-ratio data from counts at a large number of waterbodies from throughout the range statistically confirmed the preponderance of females (overall 1.0:1.2, n = 6,571), despite that juveniles of both sexes resemble adult males, which would tend to result in overestimates of males in some counts (109 Siegfried, W. R. (1976). Sex ratio in the Cape Shelduck. Ostrich 47:113–116. Close ). Subsequently, however, it was found that, although sex ratio was significantly skewed in favor of females in birds ringed at Barberspan (1.0:1.1, n = 822), the sex ratio from count data was ostensibly significantly skewed in favor of males (1.1:1.0, n = 4,103) (110 Dean, W. R. J., and D. M. Skead (1978). A note on the sex ratio in the South African Shelduck. Ostrich 49:203–204. Close ) . This was attributed to overestimates of males during counts due to the likely confusion of juvenile females with males.

This apparent female-biased sex ratio seems remarkable as it might be expected that the species’ unusual nesting habits would result in higher mortality among breeding females versus males, although it has also been suggested that burrow-nesting may be less hazardous than ground-nesting (109 Siegfried, W. R. (1976). Sex ratio in the Cape Shelduck. Ostrich 47:113–116. Close ). It has also been suggested that intense competition for breeding territories and a need for vigorous territorial defense results in increased mortality among males. Information presented for ringed juveniles at Vogelvlei (1:4, n = 114) (102 Siegfried, W. R. (1967). Trapping and ringing of Egyptian Geese and African Shelduck at Vogelvlei, Cape. Ostrich 38:173‒178. Close ) and Barberspan (1.0:1.2, n = 28) (110 Dean, W. R. J., and D. M. Skead (1978). A note on the sex ratio in the South African Shelduck. Ostrich 49:203–204. Close ), however, suggests that this biased sex ratio is present before either females or males attempt breeding. The shorter flightless period of females (due to their lighter body weight) may increase their survival compared to males, and may be responsible for the skewed sex ratio (2 Shewell, A. L. (1959). The waterfowl of Barberspan. Ostrich Supplement 3:160–179. Close ), but weight loss during wing molt apparently has little effect on survival and minimal mortality has been noted in molting flocks (9 Geldenhuys, J. N. (1983). Morphological variation in wing-moulting South African Shelducks. Ostrich 54(1):19–25. Close ).

Courtship, Copulation, and Pair Bond

Unlike at other times of the year, when the birds spend most of the day sleeping or preening along shorelines, social activity is marked during the pre-breeding period and occurs throughout the day (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 ). Courtship behavior occurs on both land and water, and in the air, and is characterized by loud vocalizations by both sexes (22 Taylor, J. S. (1944). Notes on the South African Shelduck. Ostrich 15:188–193. Close ). It can be initiated by either sex, usually more frequently by the female. Birds pursue their mates, running at or around them in a crouched posture with their necks outstretched and their bills almost touching the ground, frequently raising their heads to utter a shrill call. The female is more likely to pursue her mate than vice versa, and similar chases and circling occur on the water. The male has been reported to bob his head in response to such attention from his mate. Copulation usually occurs on the water and a pair was observed to fly there to mate. The male initially swam rapidly around the female and then mounted her by standing on her back and held her neck in his bill, submerging her except for her head and neck. Copulation lasted just a few seconds and both birds subsequently washed and preened. A similar copulation sequence has been reported, but after mating the male was noted to again circle the female, continually and stiffly raise his head and neck up and back, then lower it down and forward (2 Shewell, A. L. (1959). The waterfowl of Barberspan. Ostrich Supplement 3:160–179. Close ).

Brood Parasitism by Conspecifics

Intraspecific brood parasitism is unknown in this species (111 Geffen, E., and Y. Yom-Tov (2001). Factors affecting the rates of intraspecific nest parasitism among Anseriformes and Galliformes. Animal Behavior 62:1027–1038. Close ) and no parasitic egg-laying was found in 14 nests examined (112 Siegfried, W. R. (1964). Parasitic egg laying in South African Anatidae. Ostrich 35(1):61–62. Close ).

Degree of Sociality

In non-breeding flocks, single birds typically stay in the center, with mated pairs at the periphery (25 Brown, L. H., E. K. Urban, and K. Newman (1982). The Birds of Africa. Volume 1. Academic Press, London, UK. Close ).

Nonpredatory Interspecific Interactions

Mated pairs are intolerant of the close proximity of Egyptian Goose (Alopochen aegyptiaca) (22 Taylor, J. S. (1944). Notes on the South African Shelduck. Ostrich 15:188–193. Close ). Several chicks at solar plant evaporation ponds were believed to have been killed by Cape Teal (Anas capensis) (89 Jeal, C. (2017). The impact of a ‘trough’ concentrated solar power facility on birds and other animals in the Northern Cape, South Africa. M.S. thesis, University of Cape Town, Cape Town, South Africa. Close , 90 Jeal, C., V. Perold, S. Ralston-Paton, and P. G. Ryan (2019). Impacts of a concentrated solar power trough facility on birds and other wildlife in South Africa. Ostrich, 90(2):129–137. Close ).

Predators

Fully grown birds are taken as prey by Martial Eagle (Polemaetus bellicosus) (113 Boshoff, A. F., N. G. Palmer, and G. Avery (1990). Regional variation in the diet of Martial Eagles in the Cape Province South Africa. South African Journal of Wildlife Research 20:57–68. Close ) and Verreaux's Eagle (Aquila verreauxii) (114 Boshoff, A. F., N. G. Palmer, G. Avery, R. A. G. Davies, and M. J. F. Jarvis. (1991). Biogeographical and topographical variation in the diet of the Black Eagle in the Cape Province, South Africa. Ostrich 62:59–72. Close ). Loss of chicks is extensive in Eastern Cape Province and is attributed to predation by freshwater marsh terrapins (Pelomedusa subrufa) (92 Taylor, J. S. (1957). Notes on the birds of inland waters in the eastern Cape Province with special reference to the Karoo. Ostrich 28(1):1–80. Close ).

Response to Predators

The South African Shelduck is notoriously shy and wary in its habits (66 Horsbrugh, B. (1912). The Game-birds and Water-fowl of South Africa. Witherby and Co., London, UK. Close , 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 ).