Netta

Abstract: Summary Milstein, P. Le S. 1979. The evolutionary significance of wild hybridization in South African Highveld ducks. Ostrich Suppl. 13. Wild hybrid ducks of interspecific and intergeneric origin were unexpectedly captured at Barberspan, the major waterfowl-ringing station in Africa. In addition to a single record by Shewell (1957), 24 hybrids and back-crosses between Yellowbilled Ducks Anas undulata, Red-billed Teal A. erythrorhyncha and Southern Pochard Netta erythrophthalma were captured over a three-year period. These hybrids call for a revision of current theory concerning wild hybridization with respect to monomorphic and dimorphic ducks. Frequencies are apparently only exceeded in the literature by the controversial American Black Duck Anas rubripes x Mallard A. platyrhynchos incidence. A comparative description and statistical comparison of the different phenotypes is given. Hybrid syringes and tracheae are illustrated and compared with the parent species. The apparent evolution of a biological is...

Abstract: Summary The occurrence, chronology of breeding and wing-moult, and feeding habits of seven commonly occurring species of filter-feeding ducks on the Kafue Flats in Zambia are described, based on 20 aerial surveys over the central section of floodplain and intensive observations on the ground at Lochinvar National Park, between October 1970 and January 1974. At high flood levels ducks were almost restricted to areas heavily utilized by lechwe; this association persisted until the floodplain became dry, but during the dry season ducks were also found on vegetated lagoons. Five species—Dendrocygna bicolor, Dendrocygna viduata, Thalassornis leuconotus, Netta erythropthalma and Anas erythrorhyncha—were most abundant between June and September; a sixth—Anas punctata—was most abundant between December and March, while the seventh—Anas undulata—was probably resident. At times the numbers of D. bicolor, D. viduata and A. erythrorhyncha probably exceeded 25 000; those of N. erythropthalma reached 6500, but the numbers of T. leuconotus, A. punctata and A. undulata were much lower and at Lochinvar did not exceed 500. Small numbers of D. bicolor, N. erythropthalma, A. punctata and A. undulata nested on the floodplain in the vicinity of Lochinvar between March and July. All seven species completed their wing-moult between April and October in the area; large numbers, particularly of A. erythrorhyncha and D. bicolor, were involved. At Lochinvar, A. punctata fed mainly on aquatic invertebrates; the remaining species fed largely on shed fruits and seeds. The most important food plants were a terrestrial herb, Ambrosia maritima (January–April), two aquatic herbs, Nymphaea capensis and Nymphoides indica (May–August), and two aquatic grasses, Echinochloa stagnina and Vossia cuspidata (September–December). The herbs grew where grassland had been suppressed by lechwe; fruits of the aquatic grasses were found where lechwe had removed the overlying mat of stems. Despite similarities in diet the ducks differed from each other in feeding behaviour and/or preferred habitat. Five other species of filter-feeding ducks, Anas capensis, Anas smithii, Anas clypeata, Anas acuta and Anas querquedula, have been recorded from the Flats, but all are rare.

Abstract: The first molecular phylogenetic hypothesis for the possibly extinct pink-headed duck Rhodonessa caryophyllacea unambiguously shows that it belongs to the pochard radiation that also includes the genera Aythya and Netta. It is the sister to all modern-day pochards and belongs to a lineage that branched off from the others more than 2.8 million years ago. Rhodonessa caryophyllacea is believed to never have been common in modern time and we show this has probably been the situation for as long as 100,000 years. Our results suggest that their effective population size varied between 15,000 and 25,000 individuals during the last 150,000 years of the Pleistocene. The reasons behind this are largely unknown as very little is known about the life-history and biology of this species. Presumably it is due to factors related to feeding or to breeding, but we may never know this for sure.

Abstract: Summary Dean, W. R. J. 1978. Moult seasons of some Anatidae in the western Transvaal. Ostrich 49:76-84. Spurwinged Geese Plectropterus gambensis, Egyptian Geese Alopochen aegyptiacus, Yellow-billed Ducks Anas undulata, Redbilled Teal A. erythrorhyncha and Southern Pochard Netta erythrophthalma have a flightless moult mainly during the dry season, from April to August, in the western Transvaal. South African Shelduck Tadorna cana moult during October to February after breeding during July and August. The Cape Shoveller Anas smithii has two main flightless periods, April-May and October-January. Cape Teal A. capensis have been recorded in flightless moult in October, December and January. The duration of the flightless period correlates with wing length; larger and longer winged Anatidae require proportionally more time for wing moult than do smaller and shorter winged Anatidae. Geese and shelducks moult on large open lakes with an open shore. Ducks have been recorded flightless on lakes and dams, with or w...