|Verreaux's (Black) Eagle|
Distribution and abundance
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There is only one recognised race of this large familiar eagle which occurs as far north as Israel. In Africa it breeds in the Balé Mountains of Ethiopia (Clouet et al. 2000) where it co-exists with the Golden Eagle A. chrysaetos - its closest relative (Wink & Sauer-Gürth 2000). It is not found in otherwise suitable habitat in the Sahel (Davies & Boshoff 1997), but is widespread through eastern and southern Africa. In southern Africa it exhibits a U-shaped distribution pattern with a large gap apparent in most of Botswana and ne Namibia. This arises from the lack of prominent highlands in a region dominated by Kalahari sands. Density of breeding pairs varies from 1 pr/10.3 km2 (one of the highest known for a large eagle) in the Matobo Hills, Zimbabwe, 1 pr/24 km2 in the Karoo, SA, 1pr/25 km2 in E Africa, 1 pr/28 km2 in Ethiopia's Balé Mountains, to 1 pr/ 35 km2 - 65 km2 in the Magaliesberg and Drakensberg ranges, RSA (Brown et al. 1982, Steyn 1982, Brown 1988a, Allan 1988, Gargett 1990, Davies 1994, Clouet et al. 2000). There are no comparable figures for Namibia. However along cliffs around the Waterberg Plateau Park, pairs occur along the 150 km escarpment at a linear density 1pr/25-30 km (Brown & Cooper 1987, Simmons 2002).
The global breeding population is unknown but populations for the Cape Province South Africa, have been estimated at between 400 and 2000 pairs (Davies & Allan 1997). This allows us to estimate a slightly lower population (of c.500 - 1000 prs) for Namibia based on lower reporting rates in the Atlas (Harrison et al. 1997) in an area of similar size. Populations fluctuate surprisingly little despite four-fold changes between peaks and troughs in hyrax numbers (Davies & Ferguson 2000, R. Davies in litt); at troughs birds may temporarily disappear or switch to alternate prey. This is only especially marked in drought periods (Gargett et al. 1995) and on average occurs once every 20 yr (R. Davies in litt).
Breeding starts in April, with eggs peaking in May and extending through to August; if successful the single nestling fledges several months later in the spring and remains dependent through the summer months. Availability of prey appears to be the main determinant of timing of breeding and breeding density (Gargett 1990), but winter sheep carrion may advance laying dates in Karoo habitat (Davies 1994). Hyrax population crashes are associated more with breeding failure in eagle pairs than eagle population declines, presumably because eagles can temporarily switch to other prey (R. Davies in litt).
Breeding success recorded for a pair near Windhoek was very high with c/2 each year for 5 years and 1 young reared in 4 of the 5 years (von Ludwiger 2001).
Like other raptors they are opportunistic predators preying on medium-sized mammals such as hares, large birds (guineafowl), tortoises and occasionally carrion (Steyn 1982, Gargett 1990, Davies 1994). Prey base varies between the Karoo and Fynbos biomes with hyrax comprising 89% of prey in the Karoo and only 49% in the Fynbos (Boshoff et al. 1991). More rabbits, hares and tortoises are taken in the Karoo. Given that Verreaux's Eagles inhabit Nama Karoo and escarpment areas in Namibia, hyrax probably form the main diet in Namibia. At times Verreaux's Eagles appear capable of regulating hyrax populations by taking a significant proportion of the immatures and adults. The removal of Verreaux's Eagles, therefore, significantly increases hyrax populations in the vacuum created, increasing competition for grazing with small livestock, which in turn increases costs to small-stock farmers (Davies & Ferguson 2000). Verreaux's Eagles prefer upland areas where rocky terrain is cracked and fissured probably because its hyrax prey can always find refuge in such areas.
For a large bird of prey this species seems to be relatively immune from the depredations of farmers' poisons and guns in Namibia. Its montane habitat and low reliance on scavenging thus protect it from such mortality factors. However, this immunity is lost where sheep are farmed in or near montane areas such as the Karoo (Davies 1994). Eagles have disappeared completely only from areas where their hyrax prey has been decimated e.g. Lesotho and communal land in Matobo Hills (Davies & Allan 1997). Use and mis-use of poisons in Namibia is well known and has been responsible for the demise of scavenging species such as Tawny and Martial Eagles (Brown 1991). Thus a large predatory bird such as the Verreaux's Eagle is at risk to poisons and direct persecution. Verreaux's Eagles also drown in steep-sided farm reservoirs and they feature in the top four most likely raptors to drown: 17 drownings are recorded from arid parts of southern Africa (Anderson et al. 1999). Young occasionally disappear from well-known nest sites in Namibia and South Africa some may be due to interference by man (Allan 1988, D Hienrich in litt).
This species is classified as Near Threatened because of the threat from the high incidence of poisoning that occurs in Namibia (Brown 1991, Simmons 1995, Bridgeford 2001), and its population size of about 1000 breeding pairs. The reasonable widespread population in areas of low human density, the relative immunity from human-induced mortality in Namibia and a lack of evidence of any decline keep it from being classified as Vulnerable.
Nevertheless, poison abuse should be reduced in Namibia, free access to poisons such as Strychnine should be strictly limited by Veterinary Authorities, the beneficial nature of Verreaux's Eagles should be promoted through farmer awareness programmes; educational material for farmers and schools (developed by NARREC and the Namibian VSG) should be continued; video monitoring or a hide at appropriate nests should be experimented with for education and visitor awareness. Reservoir drownings can be prevented by farmers covering their water points with nylon mesh, keeping their reservoirs full, providing alternative drinking/bathing facilities, or attaching a log to the side on to which the bird can climb (Anderson et al. 1999).
From: Simmons RE & Brown CJ 2006. Birds to watch in Namibia: red, rare and endemic species. National Biodiversity Programme, Windhoek, Namibia
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