|Range:||Widespread, uncommon Botswana, Namibia, South Africa, Zimbabwe|
|Area of occupancy:||242,956 km2|
|Population estimate in Namibia:||< 350 pairs|
|Habitat:||Grasslands, scrubland and wooded savannas|
|Threats:||Shooting, drowning, poisons, diminishing food resources|
Distribution and abundance
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This species is a widespread but uncommon Afrotropical species found from the Sahel south to the Cape Province of South Africa (del Hoyo et al. 1994). It is locally common only in protected areas where nesting trees occur (Boshoff 1997), but it avoids dense forest habitat (Steyn 1982). It occurs right across southern Africa with concentrations in Kruger NP, and the Kalakgadi Trans Frontier Park of South Africa, and the Chobe NP, Botswana (Boshoff 1997). In Namibia it is thinly spread throughout the country, with gaps only in the Namib sand sea and some central-south farmlands where small-stock farming occurs (Brown 1991). Population concentrations occur in Etosha NP and communal land to the west, Bushmanland (Tsumkwe District) in the east, and central Namibian farmland (Brown 1991, Boshoff 1997).
The global (African) population is un-estimated but in southern Africa the highest density populations occur on rich basalt soils in Hwange NP, Zimbabwe with nesting prs 10.0 km apart. In the Kruger NP and surrounding conservation areas, pr are 11.0 km apart, and in central Namibia they are spaced 18.9 km apart in farmland (Tarboton & Allan 1984, Hustler & Howells 1990, Brown 1991, Boshoff 1993). In the Karoo, eagle densities are known to be highest (prs 7 km part) where farms are stocked with indigenous ungulates (as opposed to livestock) and primary productivity is lower (Machange et al. MS).
Two density estimates of breeding pr are available for Namibia, one inside a conservation area and one outside. In central farmland three breeding pr were found in 840 km2 giving a breeding density of 3.6 pr/1,000 km2 (Brown 1991). In the 22,700 km2 Etosha NP T. Osborne (in litt) estimated 13 pr (1 Namutoni Sandveld, 1 south of Namutoni, 3 on the s border of the Park, 1 in Goas, 1 at Homob, 1 at Olifantsbad, 1 Leeubron-Sprokieswood area, 1 Arendsnes, 1 Nomab area, 1 Rateldraf, 1 Kaross). This gives a lower density of 0.6 pr/1,000 km2 (T Osborne unpubl), but populations have not been systematically studied, and large areas of Etosha are tree-less and unsuitable for nesting.
Based on the size of the South African population which is estimated at less than 600 pr (Barnes 2000), the Namibian population with similar to lower breeding densities across an area approximately 60% the size of South Africa is estimated at less than 350 pr.
Martial Eagles inhabit a wide range of habitats including open grassland where large trees occur, and scrubby Karoo areas to wooded savanna. In modern times it has become more common in otherwise tree-less habitat such as the Nama Karoo where it nests on pylons (Boshoff 1993, Machange et al. MS). This has yet to be reported in Namibia. It avoids closed-canopy forests and hyper-arid desert but it penetrates the Namib along suitable major ephemeral rivers that flow intermittently and harbour large trees (Boshoff 1997). It is not generally found in montane areas (Steyn 1982). The diet is mainly medium-sized mammals especially hares and mongooses (63% of 403 prey) with only 8% small stock (mostly scavenged) even in areas dominated by small stock (Boshoff & Palmer 1980). In n-e S Africa, however, birds dominate the diet (45%), especially game birds, with reptiles (38%) and mammals (17%) forming a smaller proportion than in Nama Karoo habitats (Tarboton & Allan 1984, Boshoff et al. 1990). Diet is unknown in Namibia but is probably similar to the mammal-dominated diet of the Nama-Karoo study.
Adults are generally sedentary and are found in the vicinity of their large tree-nests year-round (Brown et al. 1982, Steyn 1982, Herholdt & Mendelsohn 1995). In Namibia and in the Nama-Karoo areas of South Africa (Boshoff et al. 1990) Martial Eagles generally begin breeding in winter with Namibian records from Apr (2), May (4), Jul (2), and Aug (2) (Jarvis et al. 2001).
Clutch size recorded in Namibia is invariably 1 egg (n = 7) and thus 1 young is the only recorded brood size (17 nests) but success is more difficult to gauge. In the only study Brown (1991) followed 3 prs over a 6 yr period and pairs laid on average every other year (6 eggs over 13 pr-yrs) and fledged 5 young in 6 attempts (83% success or 0.38 young/pr/yr). Only 3 young reached independence giving a lower success of 0.23 young/pr/yr - all from the same pair. From other nests in the Nest Record Scheme where young were monitored for more than 2 months, success is estimated also at 5 of 6 attempts or 83% (Jarvis et al. 2001).
Suffers direct persecution through shooting and drowning in farm reservoirs (Steyn 1982, Brown 1991, Anderson et al. 1999). In one study of a small breeding population of Martial Eagles in central Namibia, 3 breeding pr were reduced to 1 breeding pr over a 6-yr period: 4 adults were found shot and another drowned in a farm reservoir. Assuming all nests found in the 840 km2 study area were used at one time, the population probably numbered 5 breeding pr and the decline was, at 80%, even steeper than originally recorded. Elsewhere it suffers from some poisoning in South Africa so it is likely that the Namibian population also suffers to some extent. This was recorded for Namibia's oldest ringed bird and its probable mate (below) near Ondangwa, in n c Namibia (Greenwell unpubl). A more surprising threat is that of drowning in sheer-walled reservoirs. In southern Africa Martial Eagles ranked highest of all eagles as victims of drowning: of 65 eagles found dead in reservoirs, 38% were Martial Eagles (Anderson et al. 1999). These deaths were especially prevalent in more arid parts of South Africa, where an estimated 8% of the adult population may succumb to drowning (Anderson et al. 1999). This link with aridity suggests that drownings in Namibia may be more prevalent than recorded. Some mortality is associated with collisions with power lines (van Rooyen 1999): 10 birds were reported killed under powerlines by Eskom (S African supply company) in the 4 yr period from 1996-1999 (van Rooyen 1999); another 2 collided with the lines in the same period. The numbers killed in Namibia are unknown.
A further threat that may have a wider impact on Martial Eagle populations than the obvious mortalities uncovered in Brown's (1991) farmland studies is a general decline in suitable eagle prey which limits populations (A Jenkins pers comm.). This may be reflected in the larger than predicted territories of > 1,000 km2 uncovered by van Zyl (1992) and the commonly reported result of higher population densities of eagles in areas where natural prey assemblages are intact (Kruger and Hwange NPs : Tarboton & Allan 1984, Hustler & Howells 1990). This may also explain the greater eagle densities in game farms in the Nama-Karoo where large ungulates have been re-introduced compared with small stock farming areas outside (Machange et al. MS). The adult turnover in each area is needed to explain if the higher density areas are indeed source as opposed to sink populations.
Recovery from persecution will be low without immigration for several reasons - the small clutch size, the rather low breeding success varying between 0.23 young/pr/yr (Brown 1991), and 0.29 young/pr/yr in the Kgadikgadi Transfrontier Park (Herholdt & Mendelsohn 1995) to the 0.58 young/pair/yr in Nama Karoo (Boshoff 1993), and the fact that Namibian and South African birds fail to lay eggs in 66%, 50% and 38% of nests prepared (Tarboton & Allan 1984, Brown 1991, T Osborne in litt). This is peculiar to all large species but the loss of long-lived adults (oldest ringed Namibian bird 22 yr old and found poisoned: S Braine unpubl data) is a significant blow to a slowly breeding species.
This species is classified as Endangered because in central parts of their range they have declined by as much as 80% in little over 5 years through direct persecution (Brown 1991). Given that this occurred in commercial farmlands (Brown 1991) and at least 50% of Namibia's Martial Eagles are estimated to occur on commercial farmland (Boshoff 1997, Mendelsohn et al. 2002), it is likely that populations elsewhere have suffered the same declines. This is supported by the lack of recruitment into populations that have lost adults due to poisoning (Brown 1991). The small population estimated at less than 350 pr (or about 1000 individuals) also places this species in the Endangered category. While it is not classed as globally threatened because of its widespread distribution (Stattersfield & Capper 2000), it is classed as Vulnerable in South Africa where it may have lost 20% of its population in the last three generations (Barnes 2000).
Education of farmers, especially in the small-stock farming community is a priority, given the large number of Martial Eagles that die directly at the hand of man. There is little doubt that Martial Eagles do take domestic stock but studies have shown that most items are probably scavenged and form a minor proportion of all prey (Boshoff & Palmer 1980). Some adult pr tend to be much more successful than other pairs (Brown 1991), and there is strong fidelity to nest sites (Herholdt & Mendelsohn 1995). Thus highly successful (source) nests should be identified and directly protected as they are likely to add significantly to the recruitment of pairs elsewhere where breeding is less successful (sinks). Since persecution may be limiting their population size in Namibia, education and direct protection are two important aspects of conservation. Covering of farm reservoirs in arid areas will also reduce the number of birds drowning in arid areas of southern Africa (Anderson et al. 1999).
Finally and most important, additional research on important population processes such as adult survival and turnover, and the breeding frequency and success of colour marked birds (well) inside and outside protected areas should be undertaken. This will determine if protected areas remain sources for Martial Eagles in Namibia, and help differentiate between (i) degraded habitat (and low prey base) or (ii) direct mortality through persecution as the reasons for a lack of recruitment and reduced populations in Namibia. These ideas are important because a low level of persecution can be sustained by an otherwise healthy population where prey and nest sites are abundant as in certain Black Eagle populations in the Karoo that are heavily persecuted (R Davies pers comm.).
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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