06. The White Stork - going where the food is Donella Young Avian Demography Unit, UCT, Rondebosch, 7701 The White Stork Ciconia ciconia is a Palearctic migrant which usually breeds in Europe and makes the long trip through Africa to South Africa for our summer. There has been a decline in numbers in Europe, particularly Western Europe. The number of birds occurring in South Africa varies widely between years and this is probably due to factors in other parts of Africa (Allan 1997). Within South Africa this species occurs in open woodland, grassland, grassy Karoo and wetland areas, as well as agricultural cropfields and pastures, especially lucerne (Allan 1989; Rockingham-Gill & Mundy 1989). Insecticide use is not cost effective in lucerne fields and there is therefore an abundance of food in the form of insects and caterpillars (Allan 1989). The White Stork is a valuable predator on Brown Locusts Locustana pardalina in the Grassy Karoo where swarms occur (Vesey-Fitzgerald 1959; Milstein 1966). In grassland and woodland habitat, the White Stork is attracted to caterpillar outbreaks (Herremans & Herremans-Tonnoeyr 1993). The CAR (Coordinated Avifaunal Roadcounts) project has been monitoring the White Stork for the past seven years. Fig. 1 shows the network of CAR routes which are counted each summer and winter. In some areas, where routes have been established only recently, it is not possible to detect trends yet. But in other areas it is interesting to compare the results with those obtained in earlier White Stork censuses. The most recent White Stork census was conducted in 1985 by road and air; habitat use was also recorded. In that census, 86% of the storks feeding were recorded in man-altered habitats (Allan 1985). The pie chart in Fig. 2 confirms that the White Stork uses man-altered habitats extensively in the Overberg region, especially pasture and stubble fields. Fig. 3 presents the longest set of CAR results, also from the Overberg region. An exceptionally high number of birds was recorded in the summer of 1999 when there were good summer rains in this area (Hennie Lötter, pers.comm.). The results from the Karoo region (Fig. 4) show a surprisingly high number of storks (19 050) in summer 1997, which kept observers exceptionally busy! These birds were observed feeding on Brown Locusts. This locust outbreak was similar to one in February 1991, which followed good rains and attracted many White Storks (Anderson 1995). During the 1985 census very few birds were recorded in Karoo-veld, but David Allan pointed out that this habitat is attractive to these birds only after heavy rainfall (Allan 1985). The pie chart in Fig. 5 shows that the Karoo-veld was used extensively by White Stork in the summer of 1997. The 1985 census confirmed that the western KwaZulu-Natal Midlands, south to the old Transkei border, was a traditional stronghold for this species in southern Africa (Allan 1985). The CAR results presented in Fig. 6 also substantiate this; although the time series is still short, the numbers do seem to be stable in this region. However, in other regions there are unexplained fluctuations which are possibly due to the storks taking advantage of favourable conditions wherever these may be present. For example the Overberg was exceptionally dry during the summers of 2000 and 2001 and it appeared that many storks did not migrate as far south, but remained further north where there had been good rains. This confirms a pattern mentioned by Jack Winterbottom who noted that in years of good rainfall, most of the White Storks remained on the highveld in the north, but in dry years a larger proportion continued further south (Winterbottom 1977). Thus it would appear that the White Stork is opportunistic. Frans Krige, who does CAR counts in the Dullstroom area, counted over 70 White Storks feeding on an outbreak of commando worms on a farm in this area. He also reported counting 179 White Storks and 122 Abdim’s Storks within twenty minutes of setting a wheat stubble field alight. The birds seemed unafraid of the people or the flames and were in a feeding frenzy to catch the grasshoppers as they tried to fly away from the heat. There is even an interesting record of storks feeding continuously on BHC (benzene hexachloride) poisoned Brown Locust carcasses for more than a month without any apparent adverse affects! (Milstein 1966). In comparing the distribution of White Stork observed in the 1958–59 census with that in the 1974–75 census, it was noted that there was a marked westward extension along the coastal belt in the latter census (Winterbottom 1977). A comparison of the map from the 1974–75 census with that from 1985 shows a further western extension in the Overberg region in 1985. This is confirmed by atlas data (ASAB1). Fig. 7, which shows the density of birds per route in the Overberg with the routes arranged from west to east, also confirms this. (Routes OV04, 09 and 29 are just east of Caledon.) Fig. 8 shows the mean density of White Stork per region for all CAR counts. The high density in the Karoo is due to the exceptionally high number of birds observed in summer 1997. Fig. 8 indicates that parts of the Eastern Cape are also important for this species. In the most recent January 2001 CAR count, 1580 White Storks were counted along four routes in the Humansdorp district. Agricultural activities have made it possible for the White Stork to occupy parts of the Eastern and Western Cape provinces which were unsuitable before. Note that the White Stork is almost absent from the Swartland in the far west; this confirms the findings of the bird atlas of the southwestern Cape (Hockey et al. 1989). The Swartland is a wheat-growing area similar to the Overberg, and it will be interesting to see if the stork’s westward expansion will eventually include this area. CAR results have thus confirmed that the distribution of the White Stork has extended westwards, probably as a result of agricultural activities like the planting of wheat and lucerne. In some areas, such as parts of the Eastern Cape, extensive irrigation schemes have attracted White Storks. Known threats include collisions with powerlines (Oatley & Rammesmayer 1988) and occasional severe hail storms (Milstein 1966). Reasons for the low density of White Storks in Free State precincts are not obvious, especially as the original natural grasslands of this province would have provided prime habitat in the past. It may be that the use of pesticides on maize lands prevents the build up of populations of suitable prey insects. More information is needed to understand the stork’s pattern of occurrence in this province. The itinerant behaviour of the White Stork seems to be part of an opportunistic strategy to capitalize on favourable local conditions, leading to large local fluctuations in numbers of birds. Perhaps this is predictable from the facts that (a) the White Stork is a relatively large animal, (b) occurring in the region in relatively large numbers (c) during its non-breeding season (when it does not need to stay close to a nest), and (d) that it needs to maximize its nutrient intake in preparation for migration to, and breeding in, Europe. Allan D.G. 1985. White Stork Census. South African Ornithological Society. 12 pp. Allan D.G. 1989. Results of a national stork counting weekend in South Africa. In: Rheinwald, G. & Ogden, J. (eds), White Stork – Proceedings of the First International Stork Conservation Symposium. Dachverband Deutsche Avifaunisten, Braunschweig. pp. 365–371. Anderson M.D. 1995. Large flocks of storks observed feeding on Brown Locusts in the Karoo. Mirafra 12: 3–5. 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. Herremans M & Herremans-Tonnoeyr D. 1993. White Storks Ciconia ciconia, Abdim’s Storks Ciconia abdimii and Kites Milvus migrans feeding on mopane worms. Babbler 25:40. 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. Milstein P. le S. 1966. Preliminary observations of White Storks feeding on poisoned Brown Locusts. Ostrich suppl. 6: 197–215. Oatley T.B. & Rammesmayer M.A.M.1988. Review of recoveries of White Storks Ciconia ciconia in southern Africa. Ostrich 59: 97–104. Rockingham-Gill D.V. & Mundy P.J. 1989. Status and distribution of White Stork (Ciconia ciconia) in Zimbabwe. In: Rheinwald, G. & Ogden, J. (eds), White Stork – Proceedings of the First International Stork Conservation Symposium. Dachverband Deutsche Avifaunisten, Braunschweig. pp. 361–363. Vesey-Fitzgerald D.F. 1959. Locust control operations and their possible effect on populations. Ostrich 30: 65–68. Winterbottom J.M. 1977. The White Stork in South Africa, 1974–75. Ostrich 48: 116–118. Fig. 1. Map showing CAR routes (Wakkerstroom, Uniondale and Klein Karoo routes not included yet). Fig. 8. Mean and maximum (dotted line) density of White Stork per CAR precinct.

Office Avian Demography Unit
Enquiries/More Information: adu-info@uct.ac.za
Document posted: 24-Aug-2001