Sounds and Vocal Behavior

Vocal Development

Downy young give high-pitched, disyllabic distress calls (7 in 2.5s) with second syllable higher-pitched than first. Young male birds aged 2 months still peep, whereas female young have already switched voice to honking (25 Brown, L. H., E. K. Urban, and K. Newman (1982). The Birds of Africa. Volume 1. Academic Press, London, UK. Close ). Adult-like voice is established for both sexes as early as ca. 90 days old (7 Siegfried, W. R. (1966). On the post-embryonic development of the South African Shelduck Tadorna cana (Gmel.). Ostrich 37:149–151. Close ).

Vocal Array

Disyllabic honk. A distinctly disyllabic goose-like honk, typically repeated at a calm, steady pace. First syllable has a guttural tonal quality and is slightly rising, second syllable is louder, nasal trumpetlike and flat-pitched, sounding like rroh-TOO. Also described as cho-hoo' (38 Johnsgard, P. A. (1965). Handbook of Waterfowl Behavior. Cornell University Press, Ithaca, New York, USA. Close ). Total duration of honk ⁓0.30‒0.35s, with both syllables about similar length, and delivered at a pace of about 1 honk every 1‒2s. Fundamental frequency of second syllable ⁓400Hz.

Monosyllabic honk. A plaintive nasal trumpet-like hoot tooot. Note is typically overslurred, with a duration of ⁓0.35‒0.50s, much longer and marginaly higher-pitched than second syllable of Disyllabic honk. Another variant is similar, but has a distinctly rising pitch, sounding like ooah? These variants possibly have a different function.

Duet. Both members of a pair often utter their Disyllabic and Monosyllabic honk simultaneously, in an asynchronous duet.

Korr. A monosyllabic low-pitched gutural note korrr or rroh, very much like the first syllable of the Disyllabic honk. Duration ⁓0.125s.

Hiss. A threatening snake-like hissing sound is made when severely threatened, e.g. when disturbed on the nest.

Other. Both sexes give shrill screeching calls during courtship. A series of duck-like kek calls has also been observed from a female bird.

Geographic Variation

Has been regarded a superspecies together with Ruddy Shelduck (Tadorna ferruginea) (108 Johnsgard, P. A. (1978). Ducks, Geese, and Swans of the World. University of Nebraska Press, Lincoln, Nebraska, USA, and London, UK. Close ). Voice of both species has not been compared in detail, but Disyllabic honk with sudden switch from guttural to trumpet-like honking is different from homologous vocalization of Ruddy Shelduck. Within the rather limited range of South African Shelduck there is no known geographic variation in voice.

Phenology

Honking calls can be heard throughout the year, but intensity of calling is influenced by the breeding cycle, with increased calling during courtship and aggressive territorial defense during breeding. Female is quiet during incubation (July-September), in contrast with noisy behavior prior to egg-laying (25 Brown, L. H., E. K. Urban, and K. Newman (1982). The Birds of Africa. Volume 1. Academic Press, London, UK. Close ).

Daily Pattern of Vocalizing

Mainly vocal during the day, without a clear daily cycle. Vocal activity is mainly determined by daily activities, such as keeping contact with group or family members, alarming for intruders, and breeding activities.

Places of Vocalizing

Honks are given both from the ground, while swimming on the water and in flight. Pairs often duet in flight (22 Taylor, J. S. (1944). Notes on the South African Shelduck. Ostrich 15:188–193. Close ).

Sex Differences

Literature is not entirely in unison, but it is rather certain that Disyllabic honk and korrr are exclusively male vocalizations, while Monosyllabic honk is only of the female. Hissing sound can be made by both sexes.

Social Content and Presumed Functions of Vocalizations

Both male and female honking has several functions. In territorial defense, particularly in the pre-incubation period, both sexes participate, but typically the female takes the lead with loud alarm honks, inciting the male to join in (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 ). Similar calling is also observed by a mated pair when single birds approach, to defend the pair bond. Female honk is also used as an inciting call during courtship (mainly in spring), responded by male with Disyllabic honk. Outside the breeding period, honking is used as a contact between members of a pair, or when disturbance is detected. Korr call of male is more used in threatening situations, and Hiss is used in situations of imminent threat.

None documented. Wings in flight produce hardly any noise.