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Distribution, abundance and conservation of the bald ibis Geronticus calvus in Southern Africa
Biological Conservation 33 (1985) 351-362
Distribution, Abundance and Conservation of the Bald Ibis Geronticus calvus in Southern Africa D. E. Manry* Percy FitzPatrick Institute of African Ornithology University of Cape Town, Rondebosch, Republic of South Africa
ABSTRACT Updated information is provided on the breeding distribution and abundance of the bald ibis Geronticus calvus in southern Africa. Results of long-term, comprehensive surveys of the species in the Transvaal and Orange Free State are presented, and combined with information on the bird's breeding abundance in Natal to estimate its total breeding population in South Africa. The bald ibis's status in Swaziland and Lesotho is also examined. The South African breeding population is estimated at approximately 3440 birds, while its total breeding population may exceed 4600 birds. Human disturbances at its breeding sites, and degradation of its grassland biotope, pose the greatest threats to the bald ibis. Recommendationsjor improving the conservation oJ'the species are discussed.
INTRODUCTION The bald ibis Geronticus calvus is an u n c o m m o n and poorly known species endemic to the eastern highlands of southern Africa (Siegfried, 1971). Classified as rare by King (1979), the bird is confined to a restricted area in the eastern part of South Africa, ranging through the highlands of Lesotho and extending marginally into western Swaziland (Siegfried, 1971). Its sole congener, the waldrapp ibis G. eremita of N o r t h Africa and * Present address: Department of Environmental, Populational and Organismic Biology, University of Colorado, Boulder, CO 80309, USA. 351 Biol. Conserv. 0006-3207/85/$03-30 © Elsevier Applied Science Publishers Ltd, England, 1985. Printed in Great Britain
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the Middle East, has been in decline for some time and only about 400 birds remain in the wild (Kumerloeve, 1984). Like most ibis species, the bald ibis breeds in colonies, although some pairs nest solitarily. Unlike most members of its family, however, it is a cliff-nester, breeding on open ledges and in potholes on mountainsides, in river gorges, and at waterfalls. Eggs are laid from late July through midOctober, while nestlings fledge from mid-October through December. Its habitat consists of mountainous grass country, generally between 1200 and 2000 m above sea level, where it feeds primarily on insects and other small terrestrial invertebrates. Bald ibises do not undertake long migrations, but may wander for short distances within their restricted distributional range (Vincent & Symons, 1948; Siegfried, 1966a: Pocock & Uys, 1967; Cooper & Edwards, 1969; Milstein & Siegfried, 1970; Siegfried, 1971; Manry, 1982, 1984, 1985). Siegfried (1971) summarised the bald ibis's breeding status in southern Africa as it was known at that time. Since 1971, extensive survey work has been conducted in different parts of the bird's range, providing for a better understanding of its overall distribution and abundance. The aim of this paper is to present an updated review of the bald ibis's breeding distribution and abundance throughout its range, and to make recommendations for more effective conservation of the species.
BALD IBIS SURVEYS IN S O U T H E R N AFRICA Siegfried's (1966a) initial warning of the bald ibis's threatened existence stimulated amateur surveys of the species in two South African provinces (Pocock & Uys, 1967; Cooper & Edwards, 1969). In 1969, the Transvaal Nature Conservation Division initiated the comprehensive survey of bald ibis breeding localities in the province, and in 1971 the Orange Free State Nature Conservation Section began its own long-term survey (Milstein & Siegfried, 1970; Milstein & Wolff, 1973; L. P. Stoltz, pers. comm.). Both surveys focused on locating active breeding sites, censusing birds at these sites and counting nests during the breeding season. These two enquiries were officially concluded in 1977 and 1979 in the Transvaal and Orange Free State, respectively, although both organisations have continued to update their records as new breeding sites are discovered (P. le S. Milstein, L. P. Stoltz, pers. comm.). In 1982, the Transvaal Nature Conservation Division resumed its annual bald ibis survey (Allan, 1985).
Bald ibis in Southern ,4l}'ica
353
Regrettably, no official survey of the bald ibis has been conducted in Natal Province, or in the kingdoms of Lesotho and Swaziland. During 1980-1983, I compiled as many data as I could gather on the locations of bald ibis breeding sites in Natal while conducting a study of the bird's ecology and behaviour. Most information was obtained through interviews and correspondence with personnel of the Natal Parks, Game and Fish Preservation Board and the South African Department of Forestry, and from members of the Wildlife Society of Southern Africa. Appeals for information were also broadcast over national radio, and published in newsletters of local natural history societies and in a provincial newspaper. A few respondents provided information on bald ibis breeding localities in Lesotho and Swaziland, and these are also summarised here.
DISTRIBUTION A N D B R E E D I N G STATUS South Africa Transvaal
In the Transvaal, the bald ibis is confined to a narrow zone of montane grass country generally between 1600 and 2150 m above sea level along the Drakensberg Escarpment, with a single relict colony isolated in the northern part of the province approximately 175 km from the nearest other known breeding colony (Milstein & Siegfried, 1970; Milstein, 1973: Milstein & Wolff, 1973; Allan, 1985) (Fig. 1). Siegfried (1971) reported a total of 15 confirmed breeding sites in the province, with a breeding population not exceeding 450 birds. By the end of 1983, the Transvaal Nature Conservation Division had located an additional 30 breeding sites. The greatest total number of nests counted during an annual survey was 501 in 1977 (Table 1), indicating a potential breeding population of at least 1000 birds in the province. During 1973-1977, nest counts were conducted at between 20 and 34 bald ibis breeding sites in the Transvaal (Table 1). The mean number of nests counted per active breeding site ranged between 14-2 and 16.6, with an overall average of 15.2 nests per site (Table 1). In 1982, 478 nests were counted at 44 breeding sites (Allan, 1985), yielding an average of 10.9 nests per site. The lower mean number of nests per breeding site recorded in 1982, compared to the years 1973-1977 (Table 1) may be a reflection of the drought conditions that
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Fig. 1. Breedingdistribution of the bald ibis in southern Africa. Each black dot is centred in a quarter-degree square in which one or more bald ibis breeding sites have been verified.Abbreviations in inset map designate the countries of Namibia (Nam.), Botswana (Bats.), Zimbabwe (Zim.) and the Republic of South Africa (RSA). prevailed in the area during the early 1980s, relative to the high-rainfall years of the mid-1970s (Allan, 1985). Orange Free State
In the Orange Free State, the bald ibis breeds in the mountainous districts along the eastern margin of the highveld plateau and skirting the northern base of the Lesotho massif, generally between 1730 and 2200 m above sea level (Pocock & Uys, 1967; Siegfried, 1971; L. P. Stoltz, pers. comm.) (Fig. 1). Siegfried (1971) reported a total of 40 confirmed breeding sites in the province, with an estimated breeding population of ca 1000 birds. By
355
BaM ibis in Southern AJrica TABLE 1
Results of the Transvaal Bald Ibis Survey, 1973-1977 Year
No. o f breeding sites surveyed
No. o f nests counted
Average no. of nests per site
1973 1974 1975 1976 1977
20 21 31 23 34
284 348 450 357 501
14-2 16-6 14-5 15.5 14.7
129
1940
15.0
Cumulative
the end of 1982, the Orange Free State Nature Conservation Section had recorded a total of 64 active breeding sites in the province, and a total population o f ca 2400 birds, although the breeding segment was estimated at only ca 800 birds (L. P. Stoltz, pers. comm.). In a total of 34 active breeding sites censused in the Orange Free State in October 1971, the average number of nests per site was 6.5 (L. P. Stoltz, pers. comm.). Natal
In Natal, bald ibises breed at scattered localities in the eastern foothills of the Drakensbergescarpment, extending into the midlands of western Natal and northern Zululand (Vincent & Symons, 1948; Cooper & Edwards, 1969; this study ) (Fig. 1). Most breeding sites are situated between 1200 and 1900 m above sea level, although three sites verified in this study were located at exceptionally low elevations between 150 and 350 m above sea level. Siegfried (1971) reported a total of 12 breeding sites in Natal including Zululand, with a breeding population estimated at 300 birds. My own four-year survey revealed an additional 45 confirmed breeding sites scattered throughout the northern and western portions of the region (Fig. 1). Since ! was able to visit only four of these sites for the purpose of counting nests, information on the number of breeding pairs at other sites was obtained from alternative sources. Nest counts conducted during the late 1960s (six sites) and during 1978--1983 (18 sites) by reliable observers, together with my own data from four other sites during 1978--1980, provide some idea of the range and distribution of colony size and the average number of breeding pairs per site in Natal. In a total of 28
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TABLE 2
Estimation of the Total Breeding Population of Bald Ibises in South Africa (see text) Province
Transvaal Orange Free State Natal Cumulative
Average no. o f nests per site
No. o f breeding sites
Estimated no. o f breeding pairs
15.0a 6.5b 11.0c 12.9
45 64 57 166
675 416 627 1 718
a Based on nest counts conducted at 20-34 breeding sites during 1973 1977 (see Table 1). b Based on nest counts conducted at 34 breeding sites in 1971 (see text). c Based on nest counts at 28 breeding sites (see text).
breeding sites for which data were available, the average number of nests per site, 11.0, was intermediate between the values estimated for the Transvaal and the Orange Free State (Table 2).
Cape Province Bald ibises once ranged extensively throughout the southern Cape Province, occurring as far west as the Atlantic coast and breeding at several localities in the eastern Cape Province (including Transkei) around the turn of this century, but today the species no longer occurs in this region (Siegfried, 1966a, b, 1971). The last remaining breeding colony in the Cape Province reported by Siegfried (1966a, b, 1971) survives to this day, but since the magisterial district in which it is located was officially transferred to Natal Province by the South African Parliament as from 1 April 1978 (The Cape Times, 1978), the bald ibis can no longer be considered a breeding bird in the Cape Province.
Swaziland Siegfried (1971) indicated that the bald ibis ranged into western Swaziland, but provided no substantiated breeding records for the country. The bird occurs in the mountains of northwestern Swaziland, and is occasionally seen near the capital city, Mbabane (J. Culverwell, pers. comm.). At present, the only confirmed breeding sites for the species are two small nesting colonies located in the Malolotja Nature Reserve in northwestern Swaziland near the South African border (Fig. 1), where a
Bald ibis in Southern Africa
357
total of 12 pairs was observed breeding during August-October 1983 (T. Ballance, pers. comm. ). In addition, 10 bald ibises were observed in the Mahamba Gorge in southwestern Swaziland in 1979, and the species may breed in this area, although no nesting sites have been located as of yet (J. Culverwell, pers. comm.). Lesotho
Jacot-Guillarmod (1963) described the bald ibis as 'fairly common' in certain areas in the mountains of Lesotho, and this region may prove to be an important stronghold for the species. Jacot-Guillarmod (1963) lists four localities where bald ibises are known to breed in the country, while nesting colonies also exist at Sekakes, Semonkong, and Khopung Falls, although no data are available on the number of birds or breeding pairs at each site (K. Bonde, pers. comm.). The extreme ruggedness of the terrain, and the lack of roads in this remote region, would make a comprehensive survey of bald ibis breeding sites in Lesotho extremely difficult, although such a survey would be mandatory for assessing the species' overall status. ESTIMATION OF B R E E D I N G P O P U L A T I O N SIZE On the basis of the data gathered by the Transvaal and Orange Free State provincial bald ibis surveys and my own enquiry in Natal, it is possible to attempt a rough estimate of the size of the species' breeding population in South Africa, by multiplying the total number of known breeding sites by the average number of nests per site estimated for each province (Table 2). The resulting estimate of 1718 breeding pairs (or 3436 breeding birds) represents a substantial improvement over Siegfried's (1971) estimate of 2000 breeding birds, or Brooke's (1984) estimate of c. 2500 breeding birds, in all of southern Africa. It seems likely that once comprehensive data become available from Lesotho, where a sizeable bald ibis population may exist, and a more accurate assessment of the bird's status has been achieved for Natal Province, the species' total breeding population may be estimated in excess of 4600 birds. Moreover, results from the Transvaal and Orange Free State provincial bald ibis surveys suggest that the breeding segment represents approximately 42 °/o and 35 ~ of the total population, respectively. This apparent variation in the ratio of breeding to nonbreeding birds according to region merits further investigation.
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D. E. Manry
The method employed here to estimate the bald ibis's total breeding population suffers from shortcomings in the survey procedures. The species has a rather extended breeding season, and while the number of nests counted during a single visit to a colony may approximate the actual number of breeding pairs using the site, censuses conducted outside the period of peak nesting will tend to underestimate the resident breeding population, since pairs not engaged in nesting at the time of the census may be excluded from the count (Siegfried, 1971). Even at the time of peak nesting, a few pairs may not have started, or may have already failed during their initial breeding attempt but not yet renested (Manry, unpublished data), and these pairs will be excluded from nest counts as well. Moreover, the number of pairs nesting at a particular site may vary annually according to fluctuating climatic conditions, so that fewer pairs breed in drought years, and some breeding sites are not used when conditions are unfavourable for nesting (Siegfried, 1971; Milstein & Wolff, 1973; Allan, 1985; Manry, 1985; P. le S. Milstein, pers. comm.). Thus, nest counts alone are not entirely accurate measures of breeding population size at each site. Finally, small breeding colonies and single-pair nesting sites are more easily overlooked than larger colonies, so the average number of breeding pairs per site (Table 2) may be slightly overestimated. Apart from the Transvaal, where the most accurate and comprehensive data have been obtained, the estimates of the total number of breeding pairs in each province (Table 2) may be inaccurate for other reasons. Due to logistical reasons, the Orange Free State survey team was unable to visit every bald ibis breeding locality within its jurisdiction in any one particular year, requiring that fragmentary data gathered over a number of years be combined to obtain an overview of the bird's status in the province. Moreover, additional breeding sites have been located in the province since the official survey was completed (L. P. Stoltz, pers. comm.). In Natal, recent nest count data are lacking for a majority of breeding sites, so the estimated breeding population size (Table 2) may be inaccurate. HABITAT R E Q U I R E M E N T S Bald ibises inhabit open grassland, where they forage on insects and other small invertebrates in natural vegetation and in cultivated fields (Vincent & Symons, 1948; Siegfried, 1966a; Pocock & Uys, 1967; Cooper &
Bald ibis in Southern Africa
359
Edwards, 1969; Milstein & Wolff, 1973; Manry, 1982, 1984, 1985). Their breeding distribution is mainly confined to a restricted area of montane grassland, termed 'sour' because the nutritional value of its foliage to grazing ungulates decreases markedly as it matures in late summer and early autumn (Scott, 1972). Sour grassland is deliberately burned once every one to three years by landowners, usually during spring (August-October), to remove excess litter and to improve the quality of the foliage for livestock. During the prescribed winter and spring burning period, bald ibises feed extensively both in freshly burned areas and in older burns where short, post-fire regrowth is emerging, scavenging for dead insects present immediately after burning and searching for live insects that persist in or recolonise burned areas (Manry, 1982, 1984, 1985). The birds' breeding season coincides with the prescribed annual burning period, and successful breeding may partially depend on the availability of extensive areas of burned grassland (Manry, 1985). Siegfried (1966b) documented five localities in the eastern Cape Province (including Transkei) where bald ibises were recorded breeding during the mid- 19th century and the early decades of this century but have since disappeared, and attributed the species' recent decrease and extinction in this region to hunting, the loss of natural bogs and marshes to draining and livestock trampling, and the replacement of the indigenous grassland by secondary karoo vegetation following European settlement in the early 1800s. The invasion of the original sour grassland on the mountains of the eastern Cape Province by secondary macchia vegetation soon after the arrival of European settlers (Trollope & Booysen, 1971) may also have contributed to the birds' demise in this region. Only a small proportion of the total area of montane, sour grassland in southern Africa is arable, and the natural vegetation is presently used mainly for cattle and sheep production. As long as the grassland is managed properly and maintained in a vigorous condition, ranching poses little threat to the bald ibis, and may even be partially beneficial to the species (Milstein & Wolff, 1973). However, bush and karoo encroachment is still a problem in areas that are persistently overgrazed (Acocks, 1975), and any further reduction in the total area of grassland may be detrimental to the bald ibis. Another, perhaps more serious, threat to the species, particularly in Natal and the eastern Transvaal, is extensive afforestation by conifers, eucalypts and other commercially
360
D. E. Manry
valuable trees in the mesic grassland areas inhabited by bald ibises. Commercial afforestation has already contributed to the decrease of local bald ibis populations in Natal (W. R. Siegfried, pers. comm.), and further reductions in the species' range and numbers can be anticipated as more sour grassland is converted to tree plantations. CONSERVATION STATUS Bald ibises are protected by national and provincial legislation throughout their range, although adults are occasionally shot or trapped, while eggs and nestlings are removed from breeding sites to be used as food and in certain types of African tribal medicine (Vincent & Symons, 1948; Milstein & Wolff, 1973). However, human predation away from the breeding colonies is negligible, and the most serious threats to the bald ibis are human disturbances at its extremely vulnerable breeding sites, and degradation of its grassland biotope (Milstein & Wolff, 1973; Allan, 1985). In South Africa, the great majority of bald ibis breeding sites occur on privately owned land. Only seven colonies, comprising approximately 40 breeding pairs, are located in provincial nature reserves and on state forest land where they are assured adequate, long-term protection. Combining these figures with the two nesting colonies (consisting of c a 12 breeding pairs) protected in a Swaziland nature reserve, it becomes readily apparent that the bulk of the bald ibis's breeding population is dependent on the attitudes of numerous individual private landowners for its well being. These attitudes range from indifference to protectiveness towards the birds, but provide no long-term security for the species. Privately owned land in South Africa tends to change ownership on a frequent basis, so any arrangements by an individual landowner to safeguard a bald ibis breeding colony on his property can at best be considered only temporary. The most immediate requirement for conserving the bald ibis is to obtain more reliable estimates of its numerical abundance throughout its distributional range, and to implement a censusing programme to monitor its overall breeding status at regular, pre-defined intervals. The provincial bald ibis survey should be repeated as soon as possible in the Orange Free State, censusing all known breeding sites in the province and repeated thereafter at four- to six-year intervals in order to detect any possible trends in the breeding population. Meanwhile, the responsible
BaM ibis in Southern A[rica
361
nature conservation authorities in Natal, Lesotho and Swaziland should initiate their own bald ibis survey and monitoring schemes, to obtain comprehensive data on the species' distribution and abundance throughout the full extent of its range. Finally, a few of the larger breeding colonies in each territory should be purchased by the national or provincial authorities to serve as specially protected sanctuaries, to ensure that a substantial proportion of the total population is maintained under adequate safeguard. In the Transvaal, for example, purchasing the five largest colonies would result in the protection of ca 49 ~ of the total provincial breeding population (Allan, 1985). Since bald ibises regularly forage up to 20km from their breeding sites and may range even farther in their daily search for food (Manry, unpublished data), the area surrounding a breeding colony considered for special protection should be carefully assessed with respect to habitat quality, current land-use patterns, future development (especially the prospects of mining, commercial afforestation, and hydroelectric schemes), and the potential threat of bush encroachment and other forms of habitat degradation, before the site is purchased. Finally, with new techniques being developed to restore sour grassland secondarily invaded by macchia vegetation to its original condition (Trollope & Booysen, 1971 ; Downing e t al., 1978), it may be possible in the foreseeable future to reintroduce the bald ibis to parts of its former range in the eastern Cape Province (including Transkei) once grassland restoration is applied to these areas on a wide scale.
ACKN OWLEDGE MENTS I thank the Directors, Transvaal Nature Conservation Division, and Orange Free State Nature Conservation Section, for generously providing information on the breeding distribution and abundance of bald ibises in their respective provinces. I am grateful to T. C. Ballance, K. Bonde, J. M. Crowson, J. Culverwell, S. de Jager, D. Johnson, R. Little, P. le S. Milstein, L. P. Stoltz, and W. Tarboton for information on bald ibis breeding localities. I wish to acknowledge the South African Department of Forestry, the Wildlife Society of Southern Africa, and the Natal Parks, Game and Fish Preservation Board for their cooperation. I thank R. K. Brooke, R. P. Pr~,s-Jones, and W. R. Siegfried for providing helpful comments on an early draft of this paper.
362
D. E. Manry REFERENCES
Acocks, J. P. H. (1975). Veld types of South Africa. Mere. Bot. Surv. S. Afr., 40. Allan, D. (1985). The bald ibis--a false alarm? Fauna & Flora (Transraal Nature Conservation DiHsion), 42, 16-21. Brooke, R. K. (1984). South African red data book--birds. S. A[r. Natn. Sci. Progr. Rpt., 97. Cooper, K. H. & Edwards, K. Z. (1969). A survey of bald ibis in Natal. Bokmakierie, 21, 4-9. Downing, B. H., Robinson, E. R., Trollope, W. S. W. & Morris, J. W. (1978). The effects of macchia eradication techniques on botanical composition of grasses in the D6hne Sourveld of the Amatole mountains. Proc. Grassld Soc. S. Afr., 13, 111-15. Jacot-Guillarmod, C. (1963). Catalogue of the birds of Basutoland. S. Afr. Avifauna Ser., 8. King, W. B. (1979). Red data book. Ayes, part 2. Morges, IUCN. Kumerloeve, H. (1984). The Waldrapp Geronticus eremita (Linn. 1758). Historical review, taxonomic history and present status. Biol. Conserv., 30, 363-73. Manry, D. E. (1982). Habitat use by foraging bald ibises Geronticus cah'us in western Natal. S. Afr. J. Wildl. Res., 12, 85-93. Manry, D. E. (1984). Factors influencing the use of winter-burnt grassland by foraging bald ibises Geronticus calvus. S. Afr. J. Zool., 19, 12-15. Manry, D. E. (1985). Reproductive performance of the bald ibis Geronticus calvus in relation to rainfall and grass-burning. Ibis, 127, 159-73. Milstein, P. le S. (1973). Buttons and bald ibises. Bokmakierie, 25, 57-60. Milstein, P. le S. & Siegfried, W. R. (1970). Transvaal status of the bald ibis. Bokmakierie, 22, 36-9. Milstein, P. le S. & Wolff, S. W. (1973). Status and conservation of the bald ibis in the Transvaal. J. S. Afr. Wildl. Mgmt Ass., 3, 79-83. Pocock, T. N. & Uys, C. J. (1967). The bald ibis in the north-eastern Orange Free State. Bokmakierie, 19, 28-31. Scott, J. D. (1972). Veld burning in Natal. Proc. Ann. Tall Timbers Fire Ecol. Conf., 11, 33-51. Siegfried, W. R. (1966a). The bald ibis. Bokmakierie, 18, 54-7. Siegfried, W. R. (1966b). The past and present distribution of the bald ibis in the Province of the Cape of Good Hope. Ostrich, 37, 216-18. Siegfried, W. R. (1971). The status of the bald ibis of Southern Africa. Biol. Conserv., 3, 88-91. The Cape Times (1978). Transkei break: the text. The Cape Times, 11 April 1978, 2. Trollope, W. S. W. & Booysen, P. de V. (1971). The eradication of the macchia (fynbos) vegetation on the Amatole mountains in the eastern Cape. Proc. Grassld Soc. S. Afr., 6, 28-38. Vincent, J. & Symons, G. (1948). Some notes on the bald ibis. Ostrich, 19, 58-62.
Distribution, Abundance and Conservation of the Bald Ibis Geronticus calvus in Southern Africa D. E. Manry* Percy FitzPatrick Institute of African Ornithology University of Cape Town, Rondebosch, Republic of South Africa
ABSTRACT Updated information is provided on the breeding distribution and abundance of the bald ibis Geronticus calvus in southern Africa. Results of long-term, comprehensive surveys of the species in the Transvaal and Orange Free State are presented, and combined with information on the bird's breeding abundance in Natal to estimate its total breeding population in South Africa. The bald ibis's status in Swaziland and Lesotho is also examined. The South African breeding population is estimated at approximately 3440 birds, while its total breeding population may exceed 4600 birds. Human disturbances at its breeding sites, and degradation of its grassland biotope, pose the greatest threats to the bald ibis. Recommendationsjor improving the conservation oJ'the species are discussed.
INTRODUCTION The bald ibis Geronticus calvus is an u n c o m m o n and poorly known species endemic to the eastern highlands of southern Africa (Siegfried, 1971). Classified as rare by King (1979), the bird is confined to a restricted area in the eastern part of South Africa, ranging through the highlands of Lesotho and extending marginally into western Swaziland (Siegfried, 1971). Its sole congener, the waldrapp ibis G. eremita of N o r t h Africa and * Present address: Department of Environmental, Populational and Organismic Biology, University of Colorado, Boulder, CO 80309, USA. 351 Biol. Conserv. 0006-3207/85/$03-30 © Elsevier Applied Science Publishers Ltd, England, 1985. Printed in Great Britain
352
D. E. Manry
the Middle East, has been in decline for some time and only about 400 birds remain in the wild (Kumerloeve, 1984). Like most ibis species, the bald ibis breeds in colonies, although some pairs nest solitarily. Unlike most members of its family, however, it is a cliff-nester, breeding on open ledges and in potholes on mountainsides, in river gorges, and at waterfalls. Eggs are laid from late July through midOctober, while nestlings fledge from mid-October through December. Its habitat consists of mountainous grass country, generally between 1200 and 2000 m above sea level, where it feeds primarily on insects and other small terrestrial invertebrates. Bald ibises do not undertake long migrations, but may wander for short distances within their restricted distributional range (Vincent & Symons, 1948; Siegfried, 1966a: Pocock & Uys, 1967; Cooper & Edwards, 1969; Milstein & Siegfried, 1970; Siegfried, 1971; Manry, 1982, 1984, 1985). Siegfried (1971) summarised the bald ibis's breeding status in southern Africa as it was known at that time. Since 1971, extensive survey work has been conducted in different parts of the bird's range, providing for a better understanding of its overall distribution and abundance. The aim of this paper is to present an updated review of the bald ibis's breeding distribution and abundance throughout its range, and to make recommendations for more effective conservation of the species.
BALD IBIS SURVEYS IN S O U T H E R N AFRICA Siegfried's (1966a) initial warning of the bald ibis's threatened existence stimulated amateur surveys of the species in two South African provinces (Pocock & Uys, 1967; Cooper & Edwards, 1969). In 1969, the Transvaal Nature Conservation Division initiated the comprehensive survey of bald ibis breeding localities in the province, and in 1971 the Orange Free State Nature Conservation Section began its own long-term survey (Milstein & Siegfried, 1970; Milstein & Wolff, 1973; L. P. Stoltz, pers. comm.). Both surveys focused on locating active breeding sites, censusing birds at these sites and counting nests during the breeding season. These two enquiries were officially concluded in 1977 and 1979 in the Transvaal and Orange Free State, respectively, although both organisations have continued to update their records as new breeding sites are discovered (P. le S. Milstein, L. P. Stoltz, pers. comm.). In 1982, the Transvaal Nature Conservation Division resumed its annual bald ibis survey (Allan, 1985).
Bald ibis in Southern ,4l}'ica
353
Regrettably, no official survey of the bald ibis has been conducted in Natal Province, or in the kingdoms of Lesotho and Swaziland. During 1980-1983, I compiled as many data as I could gather on the locations of bald ibis breeding sites in Natal while conducting a study of the bird's ecology and behaviour. Most information was obtained through interviews and correspondence with personnel of the Natal Parks, Game and Fish Preservation Board and the South African Department of Forestry, and from members of the Wildlife Society of Southern Africa. Appeals for information were also broadcast over national radio, and published in newsletters of local natural history societies and in a provincial newspaper. A few respondents provided information on bald ibis breeding localities in Lesotho and Swaziland, and these are also summarised here.
DISTRIBUTION A N D B R E E D I N G STATUS South Africa Transvaal
In the Transvaal, the bald ibis is confined to a narrow zone of montane grass country generally between 1600 and 2150 m above sea level along the Drakensberg Escarpment, with a single relict colony isolated in the northern part of the province approximately 175 km from the nearest other known breeding colony (Milstein & Siegfried, 1970; Milstein, 1973: Milstein & Wolff, 1973; Allan, 1985) (Fig. 1). Siegfried (1971) reported a total of 15 confirmed breeding sites in the province, with a breeding population not exceeding 450 birds. By the end of 1983, the Transvaal Nature Conservation Division had located an additional 30 breeding sites. The greatest total number of nests counted during an annual survey was 501 in 1977 (Table 1), indicating a potential breeding population of at least 1000 birds in the province. During 1973-1977, nest counts were conducted at between 20 and 34 bald ibis breeding sites in the Transvaal (Table 1). The mean number of nests counted per active breeding site ranged between 14-2 and 16.6, with an overall average of 15.2 nests per site (Table 1). In 1982, 478 nests were counted at 44 breeding sites (Allan, 1985), yielding an average of 10.9 nests per site. The lower mean number of nests per breeding site recorded in 1982, compared to the years 1973-1977 (Table 1) may be a reflection of the drought conditions that
D. E. Manry
354 I
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.jr'-" ~ NATAa o~/" . "~: ao ~ " LESOTHO ~ ' o
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E31 °
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E33 ° 31°
Fig. 1. Breedingdistribution of the bald ibis in southern Africa. Each black dot is centred in a quarter-degree square in which one or more bald ibis breeding sites have been verified.Abbreviations in inset map designate the countries of Namibia (Nam.), Botswana (Bats.), Zimbabwe (Zim.) and the Republic of South Africa (RSA). prevailed in the area during the early 1980s, relative to the high-rainfall years of the mid-1970s (Allan, 1985). Orange Free State
In the Orange Free State, the bald ibis breeds in the mountainous districts along the eastern margin of the highveld plateau and skirting the northern base of the Lesotho massif, generally between 1730 and 2200 m above sea level (Pocock & Uys, 1967; Siegfried, 1971; L. P. Stoltz, pers. comm.) (Fig. 1). Siegfried (1971) reported a total of 40 confirmed breeding sites in the province, with an estimated breeding population of ca 1000 birds. By
355
BaM ibis in Southern AJrica TABLE 1
Results of the Transvaal Bald Ibis Survey, 1973-1977 Year
No. o f breeding sites surveyed
No. o f nests counted
Average no. of nests per site
1973 1974 1975 1976 1977
20 21 31 23 34
284 348 450 357 501
14-2 16-6 14-5 15.5 14.7
129
1940
15.0
Cumulative
the end of 1982, the Orange Free State Nature Conservation Section had recorded a total of 64 active breeding sites in the province, and a total population o f ca 2400 birds, although the breeding segment was estimated at only ca 800 birds (L. P. Stoltz, pers. comm.). In a total of 34 active breeding sites censused in the Orange Free State in October 1971, the average number of nests per site was 6.5 (L. P. Stoltz, pers. comm.). Natal
In Natal, bald ibises breed at scattered localities in the eastern foothills of the Drakensbergescarpment, extending into the midlands of western Natal and northern Zululand (Vincent & Symons, 1948; Cooper & Edwards, 1969; this study ) (Fig. 1). Most breeding sites are situated between 1200 and 1900 m above sea level, although three sites verified in this study were located at exceptionally low elevations between 150 and 350 m above sea level. Siegfried (1971) reported a total of 12 breeding sites in Natal including Zululand, with a breeding population estimated at 300 birds. My own four-year survey revealed an additional 45 confirmed breeding sites scattered throughout the northern and western portions of the region (Fig. 1). Since ! was able to visit only four of these sites for the purpose of counting nests, information on the number of breeding pairs at other sites was obtained from alternative sources. Nest counts conducted during the late 1960s (six sites) and during 1978--1983 (18 sites) by reliable observers, together with my own data from four other sites during 1978--1980, provide some idea of the range and distribution of colony size and the average number of breeding pairs per site in Natal. In a total of 28
D. E. Manry
356
TABLE 2
Estimation of the Total Breeding Population of Bald Ibises in South Africa (see text) Province
Transvaal Orange Free State Natal Cumulative
Average no. o f nests per site
No. o f breeding sites
Estimated no. o f breeding pairs
15.0a 6.5b 11.0c 12.9
45 64 57 166
675 416 627 1 718
a Based on nest counts conducted at 20-34 breeding sites during 1973 1977 (see Table 1). b Based on nest counts conducted at 34 breeding sites in 1971 (see text). c Based on nest counts at 28 breeding sites (see text).
breeding sites for which data were available, the average number of nests per site, 11.0, was intermediate between the values estimated for the Transvaal and the Orange Free State (Table 2).
Cape Province Bald ibises once ranged extensively throughout the southern Cape Province, occurring as far west as the Atlantic coast and breeding at several localities in the eastern Cape Province (including Transkei) around the turn of this century, but today the species no longer occurs in this region (Siegfried, 1966a, b, 1971). The last remaining breeding colony in the Cape Province reported by Siegfried (1966a, b, 1971) survives to this day, but since the magisterial district in which it is located was officially transferred to Natal Province by the South African Parliament as from 1 April 1978 (The Cape Times, 1978), the bald ibis can no longer be considered a breeding bird in the Cape Province.
Swaziland Siegfried (1971) indicated that the bald ibis ranged into western Swaziland, but provided no substantiated breeding records for the country. The bird occurs in the mountains of northwestern Swaziland, and is occasionally seen near the capital city, Mbabane (J. Culverwell, pers. comm.). At present, the only confirmed breeding sites for the species are two small nesting colonies located in the Malolotja Nature Reserve in northwestern Swaziland near the South African border (Fig. 1), where a
Bald ibis in Southern Africa
357
total of 12 pairs was observed breeding during August-October 1983 (T. Ballance, pers. comm. ). In addition, 10 bald ibises were observed in the Mahamba Gorge in southwestern Swaziland in 1979, and the species may breed in this area, although no nesting sites have been located as of yet (J. Culverwell, pers. comm.). Lesotho
Jacot-Guillarmod (1963) described the bald ibis as 'fairly common' in certain areas in the mountains of Lesotho, and this region may prove to be an important stronghold for the species. Jacot-Guillarmod (1963) lists four localities where bald ibises are known to breed in the country, while nesting colonies also exist at Sekakes, Semonkong, and Khopung Falls, although no data are available on the number of birds or breeding pairs at each site (K. Bonde, pers. comm.). The extreme ruggedness of the terrain, and the lack of roads in this remote region, would make a comprehensive survey of bald ibis breeding sites in Lesotho extremely difficult, although such a survey would be mandatory for assessing the species' overall status. ESTIMATION OF B R E E D I N G P O P U L A T I O N SIZE On the basis of the data gathered by the Transvaal and Orange Free State provincial bald ibis surveys and my own enquiry in Natal, it is possible to attempt a rough estimate of the size of the species' breeding population in South Africa, by multiplying the total number of known breeding sites by the average number of nests per site estimated for each province (Table 2). The resulting estimate of 1718 breeding pairs (or 3436 breeding birds) represents a substantial improvement over Siegfried's (1971) estimate of 2000 breeding birds, or Brooke's (1984) estimate of c. 2500 breeding birds, in all of southern Africa. It seems likely that once comprehensive data become available from Lesotho, where a sizeable bald ibis population may exist, and a more accurate assessment of the bird's status has been achieved for Natal Province, the species' total breeding population may be estimated in excess of 4600 birds. Moreover, results from the Transvaal and Orange Free State provincial bald ibis surveys suggest that the breeding segment represents approximately 42 °/o and 35 ~ of the total population, respectively. This apparent variation in the ratio of breeding to nonbreeding birds according to region merits further investigation.
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D. E. Manry
The method employed here to estimate the bald ibis's total breeding population suffers from shortcomings in the survey procedures. The species has a rather extended breeding season, and while the number of nests counted during a single visit to a colony may approximate the actual number of breeding pairs using the site, censuses conducted outside the period of peak nesting will tend to underestimate the resident breeding population, since pairs not engaged in nesting at the time of the census may be excluded from the count (Siegfried, 1971). Even at the time of peak nesting, a few pairs may not have started, or may have already failed during their initial breeding attempt but not yet renested (Manry, unpublished data), and these pairs will be excluded from nest counts as well. Moreover, the number of pairs nesting at a particular site may vary annually according to fluctuating climatic conditions, so that fewer pairs breed in drought years, and some breeding sites are not used when conditions are unfavourable for nesting (Siegfried, 1971; Milstein & Wolff, 1973; Allan, 1985; Manry, 1985; P. le S. Milstein, pers. comm.). Thus, nest counts alone are not entirely accurate measures of breeding population size at each site. Finally, small breeding colonies and single-pair nesting sites are more easily overlooked than larger colonies, so the average number of breeding pairs per site (Table 2) may be slightly overestimated. Apart from the Transvaal, where the most accurate and comprehensive data have been obtained, the estimates of the total number of breeding pairs in each province (Table 2) may be inaccurate for other reasons. Due to logistical reasons, the Orange Free State survey team was unable to visit every bald ibis breeding locality within its jurisdiction in any one particular year, requiring that fragmentary data gathered over a number of years be combined to obtain an overview of the bird's status in the province. Moreover, additional breeding sites have been located in the province since the official survey was completed (L. P. Stoltz, pers. comm.). In Natal, recent nest count data are lacking for a majority of breeding sites, so the estimated breeding population size (Table 2) may be inaccurate. HABITAT R E Q U I R E M E N T S Bald ibises inhabit open grassland, where they forage on insects and other small invertebrates in natural vegetation and in cultivated fields (Vincent & Symons, 1948; Siegfried, 1966a; Pocock & Uys, 1967; Cooper &
Bald ibis in Southern Africa
359
Edwards, 1969; Milstein & Wolff, 1973; Manry, 1982, 1984, 1985). Their breeding distribution is mainly confined to a restricted area of montane grassland, termed 'sour' because the nutritional value of its foliage to grazing ungulates decreases markedly as it matures in late summer and early autumn (Scott, 1972). Sour grassland is deliberately burned once every one to three years by landowners, usually during spring (August-October), to remove excess litter and to improve the quality of the foliage for livestock. During the prescribed winter and spring burning period, bald ibises feed extensively both in freshly burned areas and in older burns where short, post-fire regrowth is emerging, scavenging for dead insects present immediately after burning and searching for live insects that persist in or recolonise burned areas (Manry, 1982, 1984, 1985). The birds' breeding season coincides with the prescribed annual burning period, and successful breeding may partially depend on the availability of extensive areas of burned grassland (Manry, 1985). Siegfried (1966b) documented five localities in the eastern Cape Province (including Transkei) where bald ibises were recorded breeding during the mid- 19th century and the early decades of this century but have since disappeared, and attributed the species' recent decrease and extinction in this region to hunting, the loss of natural bogs and marshes to draining and livestock trampling, and the replacement of the indigenous grassland by secondary karoo vegetation following European settlement in the early 1800s. The invasion of the original sour grassland on the mountains of the eastern Cape Province by secondary macchia vegetation soon after the arrival of European settlers (Trollope & Booysen, 1971) may also have contributed to the birds' demise in this region. Only a small proportion of the total area of montane, sour grassland in southern Africa is arable, and the natural vegetation is presently used mainly for cattle and sheep production. As long as the grassland is managed properly and maintained in a vigorous condition, ranching poses little threat to the bald ibis, and may even be partially beneficial to the species (Milstein & Wolff, 1973). However, bush and karoo encroachment is still a problem in areas that are persistently overgrazed (Acocks, 1975), and any further reduction in the total area of grassland may be detrimental to the bald ibis. Another, perhaps more serious, threat to the species, particularly in Natal and the eastern Transvaal, is extensive afforestation by conifers, eucalypts and other commercially
360
D. E. Manry
valuable trees in the mesic grassland areas inhabited by bald ibises. Commercial afforestation has already contributed to the decrease of local bald ibis populations in Natal (W. R. Siegfried, pers. comm.), and further reductions in the species' range and numbers can be anticipated as more sour grassland is converted to tree plantations. CONSERVATION STATUS Bald ibises are protected by national and provincial legislation throughout their range, although adults are occasionally shot or trapped, while eggs and nestlings are removed from breeding sites to be used as food and in certain types of African tribal medicine (Vincent & Symons, 1948; Milstein & Wolff, 1973). However, human predation away from the breeding colonies is negligible, and the most serious threats to the bald ibis are human disturbances at its extremely vulnerable breeding sites, and degradation of its grassland biotope (Milstein & Wolff, 1973; Allan, 1985). In South Africa, the great majority of bald ibis breeding sites occur on privately owned land. Only seven colonies, comprising approximately 40 breeding pairs, are located in provincial nature reserves and on state forest land where they are assured adequate, long-term protection. Combining these figures with the two nesting colonies (consisting of c a 12 breeding pairs) protected in a Swaziland nature reserve, it becomes readily apparent that the bulk of the bald ibis's breeding population is dependent on the attitudes of numerous individual private landowners for its well being. These attitudes range from indifference to protectiveness towards the birds, but provide no long-term security for the species. Privately owned land in South Africa tends to change ownership on a frequent basis, so any arrangements by an individual landowner to safeguard a bald ibis breeding colony on his property can at best be considered only temporary. The most immediate requirement for conserving the bald ibis is to obtain more reliable estimates of its numerical abundance throughout its distributional range, and to implement a censusing programme to monitor its overall breeding status at regular, pre-defined intervals. The provincial bald ibis survey should be repeated as soon as possible in the Orange Free State, censusing all known breeding sites in the province and repeated thereafter at four- to six-year intervals in order to detect any possible trends in the breeding population. Meanwhile, the responsible
BaM ibis in Southern A[rica
361
nature conservation authorities in Natal, Lesotho and Swaziland should initiate their own bald ibis survey and monitoring schemes, to obtain comprehensive data on the species' distribution and abundance throughout the full extent of its range. Finally, a few of the larger breeding colonies in each territory should be purchased by the national or provincial authorities to serve as specially protected sanctuaries, to ensure that a substantial proportion of the total population is maintained under adequate safeguard. In the Transvaal, for example, purchasing the five largest colonies would result in the protection of ca 49 ~ of the total provincial breeding population (Allan, 1985). Since bald ibises regularly forage up to 20km from their breeding sites and may range even farther in their daily search for food (Manry, unpublished data), the area surrounding a breeding colony considered for special protection should be carefully assessed with respect to habitat quality, current land-use patterns, future development (especially the prospects of mining, commercial afforestation, and hydroelectric schemes), and the potential threat of bush encroachment and other forms of habitat degradation, before the site is purchased. Finally, with new techniques being developed to restore sour grassland secondarily invaded by macchia vegetation to its original condition (Trollope & Booysen, 1971 ; Downing e t al., 1978), it may be possible in the foreseeable future to reintroduce the bald ibis to parts of its former range in the eastern Cape Province (including Transkei) once grassland restoration is applied to these areas on a wide scale.
ACKN OWLEDGE MENTS I thank the Directors, Transvaal Nature Conservation Division, and Orange Free State Nature Conservation Section, for generously providing information on the breeding distribution and abundance of bald ibises in their respective provinces. I am grateful to T. C. Ballance, K. Bonde, J. M. Crowson, J. Culverwell, S. de Jager, D. Johnson, R. Little, P. le S. Milstein, L. P. Stoltz, and W. Tarboton for information on bald ibis breeding localities. I wish to acknowledge the South African Department of Forestry, the Wildlife Society of Southern Africa, and the Natal Parks, Game and Fish Preservation Board for their cooperation. I thank R. K. Brooke, R. P. Pr~,s-Jones, and W. R. Siegfried for providing helpful comments on an early draft of this paper.
362
D. E. Manry REFERENCES
Acocks, J. P. H. (1975). Veld types of South Africa. Mere. Bot. Surv. S. Afr., 40. Allan, D. (1985). The bald ibis--a false alarm? Fauna & Flora (Transraal Nature Conservation DiHsion), 42, 16-21. Brooke, R. K. (1984). South African red data book--birds. S. A[r. Natn. Sci. Progr. Rpt., 97. Cooper, K. H. & Edwards, K. Z. (1969). A survey of bald ibis in Natal. Bokmakierie, 21, 4-9. Downing, B. H., Robinson, E. R., Trollope, W. S. W. & Morris, J. W. (1978). The effects of macchia eradication techniques on botanical composition of grasses in the D6hne Sourveld of the Amatole mountains. Proc. Grassld Soc. S. Afr., 13, 111-15. Jacot-Guillarmod, C. (1963). Catalogue of the birds of Basutoland. S. Afr. Avifauna Ser., 8. King, W. B. (1979). Red data book. Ayes, part 2. Morges, IUCN. Kumerloeve, H. (1984). The Waldrapp Geronticus eremita (Linn. 1758). Historical review, taxonomic history and present status. Biol. Conserv., 30, 363-73. Manry, D. E. (1982). Habitat use by foraging bald ibises Geronticus cah'us in western Natal. S. Afr. J. Wildl. Res., 12, 85-93. Manry, D. E. (1984). Factors influencing the use of winter-burnt grassland by foraging bald ibises Geronticus calvus. S. Afr. J. Zool., 19, 12-15. Manry, D. E. (1985). Reproductive performance of the bald ibis Geronticus calvus in relation to rainfall and grass-burning. Ibis, 127, 159-73. Milstein, P. le S. (1973). Buttons and bald ibises. Bokmakierie, 25, 57-60. Milstein, P. le S. & Siegfried, W. R. (1970). Transvaal status of the bald ibis. Bokmakierie, 22, 36-9. Milstein, P. le S. & Wolff, S. W. (1973). Status and conservation of the bald ibis in the Transvaal. J. S. Afr. Wildl. Mgmt Ass., 3, 79-83. Pocock, T. N. & Uys, C. J. (1967). The bald ibis in the north-eastern Orange Free State. Bokmakierie, 19, 28-31. Scott, J. D. (1972). Veld burning in Natal. Proc. Ann. Tall Timbers Fire Ecol. Conf., 11, 33-51. Siegfried, W. R. (1966a). The bald ibis. Bokmakierie, 18, 54-7. Siegfried, W. R. (1966b). The past and present distribution of the bald ibis in the Province of the Cape of Good Hope. Ostrich, 37, 216-18. Siegfried, W. R. (1971). The status of the bald ibis of Southern Africa. Biol. Conserv., 3, 88-91. The Cape Times (1978). Transkei break: the text. The Cape Times, 11 April 1978, 2. Trollope, W. S. W. & Booysen, P. de V. (1971). The eradication of the macchia (fynbos) vegetation on the Amatole mountains in the eastern Cape. Proc. Grassld Soc. S. Afr., 6, 28-38. Vincent, J. & Symons, G. (1948). Some notes on the bald ibis. Ostrich, 19, 58-62.