|Range:||Endemic to southern Africa, isolated population in Etosha grasslands|
|Area of occupancy:||23,970 km2|
|Population estimate in Namibia:||60 birds|
|Habitat:||Wet grasslands and pans|
|Threats||Fragmented, genetically isolated? population, human encroachment|
Information on this page is from: Simmons RE & Brown CJ 2006. Birds to watch in Namibia: red, rare and endemic species. National Biodiversity Programme, Windhoek, NamibiaDistribution and abundance
Click to see distribution map
This species has the smallest range of all of the world's cranes (del Hoyo et al. 1996), and is endemic to southern Africa. It is confined to South Africa's highveld grasslands, the grain belt of the Western Cape and the eastern grassy Karoo regions, while in Namibia it is only found in Etosha National Park and the surrounding grasslands to the immediate north (Allan 1997). Birds here are distributed mainly in the wetter areas of this rather arid region (rainfall mean 440 mm). They are distributed in pairs or trios but groups up to 30 birds sometimes occur. They are associated primarily with Etosha Pan's springs which provide them with drinking water and, more importantly, safe roosting sites in the larger perennial pans (Brown 1992, Hines 1996, Simmons et al. 1996).
The species' range in South Africa is centred on the three main areas: the Overberg-Swartland region of the Western Cape, the central Karoo, northeastern Cape region, and the northeastern Free State-Mpumalanga-KwaZulu Natal (McCann 2000). There is apparently no movement between these areas and they are treated as three separate subpopulations (McCann et al. 2001). The total South African population was accurately estimated at 25,120 birds (McCann 2002), with 48% occurring in the Western Cape's grain belts.
The Namibian population has been estimated twice within the grasslands centred on Lake Oponono, between the Ekuma River in the west and Andoni in the east, and around the main salt pan of Etosha NP. In the late 1980s, Brown (1992) and T Archibald surveyed all likely areas with Etosha staff and concluded that not more than 80 birds comprise the total Namibian population. When South Africa's population decline became apparent (Allan 1994), Simmons et al. (1996) initiated a follow up estimate of Etosha's population, using volunteers, park staff and aerial surveys (C Brain) of the northern grasslands. As in earlier surveys, eastern Etosha, particularly the Andoni Flats and Namutoni, were the most utilised (73% of 60 birds) while the western drier region of Etosha was poorly populated with only seven birds recorded between Halali and Okaukuejo and two birds west of Okaukuejo at Ozonjuitji m'Bari. The northern grassland associated with the Ekuma River and Lake Oponono, surveyed from the air, realised about 10 birds, despite a lack of records from the national wetland bird surveys (Jarvis et al. 2001). Therefore, the maximum number of Blue Cranes associated with Etosha's grasslands inside and outside the Park is about 60 birds, of which 18% (11) are yearlings. This represents a 25% decline in 6 to 8 yrs. The single most important site where birds assemble to roost is the Andoni water hole with up to 30 birds. A recently completed survey by the newly formed Blue Crane Working Group in 2006 indicated about 62 adults with 7 young birds with concentrations at the flooded Lake Oponono and Ekuma River and another concentration around Fischer's Pan (Simmons et al. 2006). These figures suggest the population has stabilised and continues to breed.
The question arises how isolated is the Namibian population? The available evidence from studies of movements (in South Africa) show that no colour ringed birds from one of the three subpopulations has ever been found to move to another population (K McCann in litt); the furthest moved by 27 birds recovered from 65 ringed was 426 km, within one subpopulation (McCann et al. 2001). Satellite tagged birds have virtually stayed stationary over a 2-year period (McCann et al. 2001); and lastly, breeding seasons of the southern African and Namibian populations are spaced about 3 months apart (below). Recent genetic evidence suggests that Etosha's birds are isolated and preliminary evidence indicates that they can indeed be differentiated from South African populations (M Wink in litt).Ecology
Found primarily in dry grassland habitat where water regularly occurs (McCann 2000). In the arid grasslands of Etosha NP the favoured areas are the perennial springs around the pan edge and isolated water holes in grassy plains such as Andoni (Brown 1992, Simmons et al. 1996). Nests occur on the ground in open grassy areas, not far from water, such that chicks may be led to water to drink and escape predators. One bird nested on an island in Fischer's Pan (T Osborne pers obs). Birds feed on seeds and flowers from grasses, and frogs, reptiles, and fish (Maclean 1993). In Etosha birds regularly turn over elephant and ungulate dung to consume dung beetles and other insects (RE Simmons pers obs).
Pre-breeding groups of between 6 and 30 birds are not uncommon and twenty records of active nests indicate that egg-laying occurs December - March with a peak in February (Brown 1992). A larger sample (n = 33), including the Brown (1992) records from the Namibian Avifaunal database (Jarvis et al. 2001), indicates that nests with eggs were found in January (2), February (4), March (2), June (1). Nests with chicks were found from January (2), February (9), March (9), April (2), May (1), and October (1). This is several months later than the September-January breeding season in South Africa (Allan 1997), and particularly the October - December peak in the grasslands of South Africa (Allan 1993). Average clutch size is 1.71 (n = 7), with two one-egg clutches and five two-egg clutches the only clutches recorded in Etosha. Nests are recorded from Batia (Namutoni), Twee Palms (commonly) Chudop, Andoni Vlakte, Fischer's Pan and the Halali Plains (Jarvis et al. 2001). Brood size varied from one to three (chick sizes not given) with broods of two (n = 12) more common than broods of one (n = 8) or three (n = 1) (Jarvis et al. 2001).Threats
The 25% decline in population size in Etosha is unexplained (Simmons et al. 1996). Lower than typical rainfall through the late 1980s and early 1990s in northern Namibia (Mendelsohn et al. 2002) could explain poorer recruitment and lowered populations, even though 18% of the population in 1996 were yearlings, indicating that breeding does continue at such times. Expanding human populations in northern Namibia, and the encroachment of local people with cattle into the grasslands north of Etosha will eventually drive cranes from these areas. Lake Oponono for example, with its fresh water, is a focal point for cattle and people who place snares in many trees and other roost areas to capture and eat birds (W Versfeld pers obs). Instances of cranes being killed are unknown but not unlikely, and collisions with power lines in the eastern grasslands of Etosha are possible given that Blue Cranes are known to be highly vulnerable to powerline collisions in South Africa (McCann 2000). Furthermore the pan's springs are fed by aquifers that drain towards this lowest part of northern Namibia (Christelis & Struckmeier 2001), and increased human population size and bore hole drilling in the north will probably eventually reduce the permanence of these perennial springs, driving cranes away.
Elsewhere in South Africa, poisoning (direct and indirect) in agricultural fields and loss of habitat due to afforestation and agricultural ploughing have been the two main contributory factors to population decline (Allan 1997, McCann 2000). This is not apparently a problem in Namibia. Isolated and small populations can be prone to inbreeding effects if genetic heterogeneity has been lost (Westemeier et al. 1998); this could apply to Etosha's cranes given the small breeding population of 24 pairs (Simmons et al. 1996), and their apparent genetic isolation (M Wink in litt). This, disease and catastrophic events such as severe drought under global climate change could push such a small population to extinction within a generation or two.Conservation Status
This species is classified as Critically Endangered in Namibia because of its tiny population size, and the 25% decline since the late 1980s. It is additionally highly isolated given that the closest breeding populations are found in the North West Province of South Africa, over 1,000 km to the south east. Thus little immigration, if any, is likely given that the longest movement of a Blue Crane ever recorded was 426 km and most populations are sedentary (Underhill et al. 1999, McCann et al. 2001); the Etosha population must be self-sustaining. Its global (Stattersfield and Capper 2000) and South African (McCann 2000) populations are categorised as Vulnerable given the healthier (25,000 birds) but declining populations there.Actions
Five-yearly total population assessments - coinciding with Etosha aerial game counts - should be conducted to assess populations continually. If low rainfall is the root cause of decreasing populations then increased populations (and recruitment) are expected following high rainfall years. Areas such as Lake Oponono, covered well during wetland monitoring (W Versfeld), should be continually checked for cranes and other areas in the northern Etosha grasslands should be systematically searched for (all) cranes. Critical waterholes (e.g. Andoni and Twee Palms) should be given special attention and should be pumped when necessary to maintain levels during drought periods.
Given the sedentary nature and different breeding periods of Etosha's cranes their genetic status should be further investigated to determine if inbreeding effects are likely. Blood samples can be collected from flightless chicks to cause the least disturbance. A colour-ringing study will assist in determining population size, the residence and survival of select pairs, and low level studies of their movements and use of habitats around Etosha will assist in identifying critical areas which should be given conservation attentionReferences
Allan DG 1993. Aspects of the biology and conservation of the Blue Crane Anthropoides paradiseus, and the Ludwig's Neotis ludwigii and Stanley's N. denhami stanleyi Bustards in southern Africa. MSc thesis, University of Cape Town.
Allan DG 1994. Haven for Blue Cranes. African Wildlife 48:8-14.
Allan DG 1997. Blue Crane. In: Harrison JA, Allan DG, Underhill LG, Herremans M, Tree AJ, Parker V, Brown CJ (eds). The Atlas of Southern African Birds. Vol. 1: 314-315. BirdLife South Africa, Johannesburg.
Barnes KN (ed) 2000.The Eskom Red data book of birds of South Africa, Lesotho and Swaziland.
Brown CJ 1992. The status of cranes in Namibia. Pp 73-78 In: Proc. 1st Sthn Afr. Crane Conf. Natal.
Christelis G & Struckmeier W (eds) 2001. Groundwater in Namibia and explanation of the hydrogeological map. Ministry of Agriculture, Water and Rural Development, Windhoek
Del Hoyo J, Sargatal J & Elliot A 1996. Handbook of the Birds of the World. Vol 3 Hoatzins to Auks. Lynx Edicions, Barcelona, Spain
Jarvis AM, Robertson A, Brown CJ & Simmons RE 2001. Namibian avifaunal database. National Biodiversity Programme, Ministry of Environment & Tourism, Windhoek
Hines CJH 1996. Cranes in Namibia In: Beilfuss RD Tarboton WR Gichuki NN (eds) Proceedings of 1993 African crane and wetland training workshop. Pp 305-306, International Crane Foundation Baraboo Wisconsin USA
Maclean GL 1993. Roberts Birds of Southern Africa. John Voelcker Bird Book Fund, Johannesburg.
McCann KI 2000. Blue Crane In: Barnes KN (ed).The Eskom Red data book of birds of South Africa, Lesotho and Swaziland. Pp92-94. Birdlife South Africa, Johannesburg.
McCann KI, Shaw K, Anderson MD & Morrison K 2001. Techniques for determining movement patterns of Blue and Wattled Cranes in South Africa - colour ringing versus satellite telemetry. Ostrich Supplement 15: 104-108.
McCann KI 2002. Results of the 2002 National Crane census. Unpublished Report, Endangered Wildlife Trust, Johannesburg.
McCann, Kevin personal communication
Mendelsohn JM, Jarvis AM, Roberts C & Robertson A 2003. Atlas of Namibia: a portrait of the land and its people. David Phillip Cape Town.
Stattersfield AJ & Capper DR (eds) 2000. Threatened Birds of the World. Birdlife International, Cambridge.
Underhill LG, Tree AJ, Oschadleus HD & Parker V 1999. Review of ring recoveries of waterbirds in southern Africa. Avian Demography Unit, University of Cape Town
Westemeier RL, Brawn JD, Simpson SA, Esker TL, Jansen RW, Walk JW, Kershner EL, Bouzat JL & Paige KN 1998. Tracking the long-term decline and recovery of an isolated population Science 282: 1695-1698.