15. Changes in distribution and abundance of waterbirds in South Africa D.M. Harebottle & J.A. Harrison Avian Demography Unit, UCT, Rondebosch, 7701 Following on from the article ‘Changing suburban birds – terrestrial species’ in Bird Numbers 9(2), this article focuses on waterbirds. We will look at urban environments but also consider larger scale distributional changes over the last 30–40 years. – Ed. Habitat changes The destruction of wetlands has a negative impact on waterbirds, but waterbirds are adapted to exploit constantly changing conditions, especially in a relatively arid region such as southern Africa. Waterbirds will naturally move in response to changing water levels, food availability, etc. When a wetland is destroyed by draining or infill, or damaged by pollutants or nutrient-overloads, or becomes too disturbed by recreational activities, most waterbirds will simply vacate and move off in search of another suitable site. (This is not to say that reduction in available habitat does not have a long-term negative effect on populations.) The creation of artificial wetlands provides waterbirds with alternative options and, if conditions are good, will attract an array of species over time. The itinerant and opportunistic nature of waterbirds, coupled with changes in the availability of habitat, result in changes in distribution and local abundance. An example of short-term exploitation of newly created habitat is the response of waterbirds to the construction of a storm-water retention dam at a new development, Century City, in Cape Town. To enhance the aesthetics of the dam, a rocky island was created in the centre, and reeds were planted along the banks. Within a year, Redknobbed Coot Fulica cristata, Cape Shoveller Anas smithii and Dabchick Tachybaptus ruficollis, among others, had settled on the dam, and within three years a colony of over 1000 pairs of Hartlaub’s Gulls Larus hartlaubii had adopted the island as the species’ principal breeding site (see BN 9(1)). Sewage and waste-water treatment works create a mosaic of habitats, such as open water, reedbeds, exposed shoreline and shallow mud flats. These environments are believed to have encouraged range expansion and, in some cases, subsequent residency of several species. In the southwestern Cape, localities such as the Strandfontein and Paarl sewage works have probably aided the westward expansion of species like Glossy Ibis Plegadis falcinellus, Sacred Ibis Threskiornis aethiopicus, Hottentot Teal Anas hottentota and Whitefaced Duck Dendrocygna viduata. Water supply at these facilities is regulated and often maintained at constant levels, and this permanent supply of water is attractive to many species. In fact, sewage works are sometimes more productive in terms of numbers and variety of species than some large natural wetlands. Strandfontein Sewage Works, on average, accommodates 2–3 times more birds than Lake St Lucia and, on occasions, as many birds as Langebaan Lagoon! Sportsfields, golf-courses and racecourses are attractive to many species including Hadeda Ibis Bostrychia hagedash, Sacred Ibis, Egyptian Goose Alopochen aegyptiacus, Cattle Egret Bubulcus ibis and Blackheaded Heron Ardea melanocephala. The presence of large trees (usually Pinus and Eucalyptus spp.), at or around these areas, provide suitable nesting sites for some of the larger waterbirds. Agricultural landscapes can be beneficial to certain waterbirds and are likely to have contributed to range expansion in some species. Egyptian Goose, Spurwinged Goose Plectropterus gambensis and Blackheaded Heron are species that are often found in large numbers in pastures, irrigated lands and croplands. The construction of farm dams has also provided additional aquatic habitats and many species can now be found breeding and/or roosting at these dams. Cormorants, egrets and herons are often found in mixed heronries at large farm dams that contain suitable nesting structures (e.g. large trees situated on the edge of the wetland or on an island). Other developments that could influence suburban waterbird abundance are botanical gardens. Most are situated within or peripheral to large cities or towns and, although they do not always contain large waterbodies, they do provide certain landscape elements that attract waterbirds (see Nuttall 1994). In addition, gardens that have water features, fish ponds or, in some cases, patches of natural wetland habitat, can provide suitable micro-habitats for certain species such as wagtails and kingfishers. There are many wetlands, both natural and artificial, around which suburbs and industrial precincts have developed (e.g. Rietvlei and Seekoeivlei in Cape Town, the Benoni Lake complex on the East Rand), and the changes such developments cause at these wetlands can play a role in changing local waterbird communities. Much depends on the sensitivity – or lack of it – shown to the functioning of wetland ecosystems. This is an area in which most engineers and developers still have much to learn. Selected examples From corroborating evidence gathered from informal surveys on SABIRDNET, and from bird club newsletters, published material and data from the Coordinated Waterbird Counts (CWAC) database, we have selected species to illustrate relatively recent changes in waterbird abundance and distribution. Herons The Goliath Heron Ardea goliath has undergone a southern and western expansion of its range in South Africa over the past 30 years. This species was rarely recorded in the Free State and as far south as Port Elizabeth, and was absent from the lower Orange River and southern Namibia (McLachlan & Liversidge 1970; Maclean 1985). Eight years later, Maclean (1993) showed the distribution covering southern Namibia, including the lower Orange River, and certain areas in the Eastern Cape, as far south as Port Elizabeth. None of these publications mentioned any records from the Western Cape or northern Karoo. Hockey et al. (1989) did not record it from 1982–86 and stated that it is a vagrant to the southwestern Cape, with only two known records – one from Zoetendalsvlei in the 19th century and the other from Cape Agulhas in 1957. Prior to 1990, the most westerly record was just west of 25°E (2924DC), in the south-western Free State (Earle & Grobler 1987). More recent atlas data, 1987–92 (ASAB1), showed how the species’ range had expanded in the southwest, penetrating the central and south-eastern parts of the Karoo. It also confirmed the species’ occurrence on the lower Orange River, from Upington down to the mouth, an area now considered prime Goliath Heron territory. ASAB1 still indicated an absence of Goliath Herons from the south-western Cape. However, in the last seven years, 1994–2000, there have been numerous records from several localities in the south-western Western Cape Province, including four from Verlorenvlei, three from the lower Berg River, one from Koeberg Nature Reserve, and one from Paarl Sewage Works, the last-mentioned individual remaining at the locality for several months before leaving. (CWAC data; Y. Weiss in litt.). In addition, there has been a recent (May 2001) record from Oudtshoorn sewage works. This recent increase in the number of westerly records may be early evidence of a westerly range expansion. However, these birds are known to move long distances in response to changing water levels (Martin 1997) and, in the absence of records of breeding or residency, the Goliath Heron may remain an irregular visitor to the south-west. It is interesting to note records from sewage works, a habitat not previously mentioned for this species and which may be aiding its spread westward. Elsewhere in South Africa, Goliath Herons have their highest concentrations at many of the large state dams with few natural wetlands holding large numbers of birds. The Great White Heron Casmerodius albus is most abundant at the larger waterbodies in central and north-eastern South Africa (e.g. Lake St Lucia, Pongolapoort Dam, Bloemhof Dam, Spitskop Dam and Barberspan) and is generally sparsely distributed elsewhere. It is described as being nomadic and dispersive, moving to areas with suitable feeding and breeding habitat (Brown et al. 1982). ASAB1 showed low reporting rates for the Western and Northern Cape, and some seasonal variation in the Eastern Cape. Hockey et al. (1989) described it as an erratic summer visitor to the south-western Cape, but mentioned that it was being recorded more frequently in the region. Relatively recent CWAC data confirm numerous winter observations in the south-western Western Cape. Observations from Namaqualand, e.g. Gariep and the lower Orange River during May and June respectively, provide evidence that birds may be resident throughout the year (Allsop et al. 1991; Euston-Brown 1993). The species was not recorded in these parts in ASAB1. Great White Herons have also been reported from some suburban or built environments, including a section of the Liesbeeck River in Cape Town (Kirsch 1990), the small Klavervlei dam near Somerset West (Kakebeeke et al. 1991), irrigated rugby fields (Allsop et al. 1991) and, more recently, at Century City, Cape Town (M. Maciver in litt.), where artificial wetlands have been created adjacent to a large shopping complex. It seems possible that these two largest ardeids, the Goliath and Great White Herons, are, by adapting to smaller wetlands, closer to human habitation, expanding their ranges and probably recapitulating patterns of expansion set much earlier by the smaller members of the family, such as the Cattle Egret, Little Egret and Grey Heron. Both species have benefited from the construction of large impoundments, especially those in the Free State, and these have probably provided nuclei from which further range expansion has taken place (ASAB1). Ducks Many ducks are nomadic and undertake local movements in response to food availability, fluctuations in water-level and/or rainfall (Maclean et al. 1997) . These movements are not fully understood but it is possible that in search for more suitable habitat, range expansions could occur. Two species, Whitefaced Duck Dendrocygna viduata and Hottentot Teal Anas hottentota, were absent from, or vagrants to, the south-western Western Cape in the 1970s and early 1980s. These birds are now regularly recorded throughout the year, although in small numbers, at several localities on the Cape Peninsula (Schmidt & Schmidt 1993; Dorse 1997; Anon. 2000), the teal also having been recorded breeding at Strandfontein Sewage Works (McCarthy 1990). Waterbird counts at Paarl and Oudtshoorn sewage works seem to suggest that numbers of Whitefaced Duck are on the increase and that they favour these wetland conditions. This species has undergone a similar increase in Port Elizabeth where they were recorded as vagrants during the 1980s; they are now seen regularly at various wetlands in and around the city. Fulvous Duck Dendrocygna bicolor seems to have increased in certain areas. In Port Elizabeth it was vagrant during the 1980s but is now recorded regularly, with the first known breeding record made in December 1999. In the south-western Western Cape, CWAC counts from 1992–99 show some variation in numbers and, although present in low numbers, they do seem to be more numerous and recorded more frequently than during the late 1970s and 1980s (Hockey et al. 1989). Of all the Anatidae, the Egyptian Goose is probably the species which has been able to adapt to the greatest variety of habitats. Normally associated with any waterbody, although occurring in higher numbers at large, permanent wetlands, these birds can regularly be found in cultivated fields, sportsfields, suburban open spaces, and even in the CBD of some cities. In Cape Town’s southern suburbs, the species has become more common in recent years and individuals can often be seen perched on roadside lampposts and rooftops (DH pers. obs.). The species’ ability to habituate to humans and the built environment has enabled it to exploit additional feeding and breeding opportunities. This species’ habit of nesting in trees has no doubt played a role in attracting it into the suburbs. In contrast, CWAC data show numbers decreasing at certain localities (e.g. Pongolapoort Dam, Nyamithi Pan), while there have been reports of increases in suburbs such as Rivonia (Jhb), Rondebosch (CT), Bellville (CT), Durbanville (CT) and in Nelspruit. The Egyptian Goose is regarded as a pest in some agricultural communities because of the damage it does to young crops. For this reason it is hunted in some areas. On the other hand, the attitude of people in the middle-class suburbs of the big cities has become progressively more tolerant and favourable towards wildlife, especially birds, with the result that breeding and the rearing of chicks is generally safer and, in some cases, actively aided by nature lovers. These factors may be behind different demographic trends in different areas. Woollynecked Stork The Woollynecked Stork Ciconia episcopus breeds, and is resident, in the north-eastern lowveld areas of South Africa, although it is suspected that some birds move south along the KwaZulu-Natal coast, especially during the rainy season (Berruti 1997). This southward movement appears to have contributed to the birds becoming more common in southern KwaZulu-Natal. These storks are known to occur in a variety of wetland habitats, including rivers, pans, estuaries and floodplains, and require large trees, usually riparian, for breeding (Scott 1975). It has been suggested that the species’ ability to adapt to non-wetland habitats, such as golf courses, firebreaks and roads in sugar-cane plantations, has led to the apparent extension of its range in southern KwaZulu-Natal (Berruti 1997). There are now frequent reports from a suburban park in Pinetown and recorded breeding from a small natural enclave in suburban New Germany. Some individuals are even known to visit a garden in New Germany where they feed on left-over dog food. CWAC has reported Woollynecked Storks from several man-made habitats, including sewage treatment works (Northern Treatment Works and St Lucia Sewage Works), aquaculture stations (Mtunzini Prawn Hatchery) and mine dams (Palabora Mining Company). The utilization of man-made habitats was not previously mentioned for this species, indicating that its adaptation to artificial habitats is a relatively recent phenomenon. The use of sewage works, in particular, may be an important contributing factor to the spread and abundance of the Woollynecked Stork in southern KwaZulu-Natal. Ibises Ibises will be discussed in a future article. Acknowledgements We wish to thank all those observers who responded to the informal survey on SABIRDNET (M. Brown (Pmb), C. Cilliers (Stell.), W. Collingwoods (Newcastle), W. du Buy (CT), P. Lawson (Nelspruit), P. Martin (PE), T. Snyman (Durb.), D. Whitelaw (CT)) as well as all CWAC participants. Anderson M.D. 1997. Glossy Ibis Plegadis falcinellus. In: Harrison J.A., Allan D.G., Underhill L.G., Herremans M., Tree A.J., Parker V. & Brown C.J. (eds).The atlas of southern African birds. Vol. 1: Non-passerines. pp. 106–107. BirdLife South Africa, Johannesburg. Anon. 1991. Promerops 200: 16 Anon. 2000. Interesting sightings. The Batis 4: 21 Allsop B., Thomson P. & Thomson M. 1991. Great White Egret in Namaqualand. Promerops 199: 10 Berruti A. 1997. Woollynecked Stork Ciconia episcopus. In: Harrison J.A., Allan D.G., Underhill L.G., Herremans M., Tree A.J., Parker V. & Brown C.J. (eds). 1997. The atlas of southern African birds. Vol 1: Non-passerines. pp. 89–91. BirdLife South Africa, Johannesburg. Dorse C. 1997. Rondevlei news – Making way for fynbos. Promerops 229: 10 Earlé R.A. & Grobler N.J. 1987. First atlas of bird distribution in the Orange Free State. National Museum, Bloemfontein. Euston-Brown M. 1993. Orange River birds. Promerops 209: 11 Fraser M. & McMahon L. 1991. Sacred Ibises on the southern Peninsula. Promerops 198: 7 Harrison J.A., Allan D.G., Underhill L.G., Herremans M., Tree A.J., Parker V. & Brown C.J. (eds). 1997. The atlas of southern African birds. Vol. 1: Non-passerines. BirdLife South Africa, Johannesburg. Hockey P.A.R, Underhill L.G., Neatherway M. & Ryan P.G. 1989. Atlas of the birds of the southwestern Cape. Cape Bird Club, Cape Town. Kakebeeke B., Lamont G. & Scott J. 1991. African Jacanas and Great White Egrets at Klaver Vlei. Promerops 198: 7 Kirsch B. 1990. Sightings – Great White Egret. Promerops 191: 15 Maclean G.L. 1985. Roberts’ birds of southern Africa – Fifth edition. John Voelcker Bird Book Fund, Cape Town Maclean G.L. 1993. Roberts’ birds of southern Africa – Sixth edition. John Voelcker Bird Book Fund, Cape Town Maclean G.L., Spottiswoode C.N., Cohen C. & Harrison J.A. 1997. Family Anatidae: ducks, geese and swans. In: Harrison J.A., Allan D.G., Underhill L.G., Herremans M., Tree A.J., Parker V. & Brown C.J. (eds). The atlas of southern African birds. Vol. 1: Non-passerines. BirdLife South Africa, Johannesburg. pp. 116–150. Martin A.P. 1997. Goliath Heron Ardea goliath. In: The atlas of southern African birds. Vol. 1: Non-passerines. Harrison J.A., Allan D.G., Underhill L.G., Herremans M., Tree A.J., Parker V. & Brown C.J. (eds). pp. 116–150. BirdLife South Africa, Johannesburg. McCarthy M. 1990. Sightings – Hottentot Teal. Promerops 194: 16 Mclachlan G.R. & Liversidge R. 1970. Roberts’ birds of South Africa. John Voelcker Bird Book Fund, Cape Town Mearns C. 1990. Founder’s Day outing to Wildevoëlvlei, near Kommetjie. Promerops194: 16–17 Middlemiss E. 1955. Nest of Glossy Ibis at Rondevlei. Ostrich 26: 137–138. Neall P.J.P. 1952. Points from letters. Ostrich 23: 62 Nuttall R.J. 1994. Sightings of interest – OFS region. Mirafra 11(2): 32 Schmidt O. & Schmidt, R. 1993. Sightings – Whitefaced Duck. Promerops 209: 12 Scott J.A. 1975. Observations on the breeding of the Woollynecked Stork. Ostrich 46: 201–207

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Document posted: 24-Aug-2001