| Booted eagle | |
| Aquila pennatus minisculus | |
| Status: | Endangered |
| Range: | Botswana, Namibia, South Africa, Zimbabwe |
| Area of occupancy: | 109,082 km2 |
| Population estimate in Namibia: | 20 prs, 250 individuals |
| Population trend: | Fluctuating according to conditions |
| Habitat: | Mountains, inselbergs |
| Threats: | Small population fluctuations |
Distribution and abundance
 Click to see distribution map |
This is both a palearctic migrant to southern Africa and a breeding species within s Africa (Brooke et al. 1980, Steyn 1982). Palearctic migrants leave in March but confusion occurs because s African breeding populations also show migratory movements within s Africa (Tarboton & Allan 1984, Boshoff & Allan 1997). It has been suggested that three populations occur in Namibia: (i) palearctic migrants, present from November-March; (ii) non-breeding migrants from the South African breeding population, present March-July; and (iii) Namibian breeding birds present March - December (Brown & Cooper 1987). The latter breeding population of Booted Eagles is more probably a northward extension of the South African breeding population. Indeed this species, the commonest eagle in the w Cape Province with an estimated population of 702 prs (Pepler et al. 2000) was overlooked as a breeding species in South Africa before the mid 1970s (Brooke et al. 1980). Importantly it is now recognized as a genetically distinct subspecies (see Conservation below), significantly smaller than the Palearctic race (Yosef et al. 2000).
The area of occupancy in Namibia covers 109,082 km2 but this includes both migrant and breeding birds. That for breeding (resident) birds is smaller at about 70,700 km2 and generally in western Namibia. They have been recorded in winter from the Waterberg Plateau (up to 8 birds: Brown & Cooper 1987), in the Kaokoveld Mountains in nw Namibia, where birds were performing undulating flights (S Braine in Brown & Cooper 1987), 2-3 birds from the Erongo mountains (RE Simmons pers obs), 3-4 birds at the Spitzkoppe inselberg (RE Simmons, C Boix-Hinzen pers obs), from the Brukkaros crater (up to 5 birds and possible breeding: Scholtz 2005, Simmons & Barnard in press, CJ Brown pers obs), and from the Namibian section of the Orange River in June (A Jenkins pers obs), where 5 birds and two possible nests sites were recorded in 50 km in December (Simmons & Allan 2002). If all the areas mentioned have breeding pairs when conditions are favourable, at least 20 prs may breed in Namibia. Raptor road counts in the winter months in 1985 when breeding was discovered were higher (at 4.6 birds/1000 km) than at any other time in the period 1981-1997 (Jarvis et al. 2001). This may only occur when rains are favourable and bird prey more numerous.
Ecology
Occurs in a wide variety of arid open habitats largely associated with mountainous country and adjacent plains. In Namibia it is associated with inselbergs in western parts and in South Africa it is particularly common in the Little Karoo and along the Great Escarpment of the Great Karoo (Martin 2005). Most frequently hunts over plains of dwarf shrubs and scattered stunted trees (Martin 2005). The mechanical removal of bush for agricultural purposes and the provision of water throughout arid area may have opened up feeding areas previously unsuitable for hunting (Brown & Cooper 1987, Martin 2005). Most hunting is done on the wing with prey caught in spectacular stoops; about 55% of prey items are birds, lizards comprise 33% and rodents 13% (Steyn 1982). Doves and francolin are the only recorded prey from Namibia (Brown 1985). Three nests have been reported from Namibia, from the sandstone cliffs of the Waterberg Plateau Park (Brown 1985, Brown & Cooper 1987). Others are suspected from the Spitzkoppe (RE Simmons, C Boix-Hinzen pers obs), the Orange River around Noordoewer (Simmons & Allan 2002), and probably on inselbergs in other parts of Namibia when conditions allow. Given their small size and placement behind small shrubs on cliff faces (Brooke et al. 1980, Brown 1985) it is likely that nests are overlooked between these two locations. Egg laying has occurred in Namibia in June (Brown 1985), and in South Africa in September (Brooke et al. 1980, Anderson et al. 1995). Typical clutch size is 2 with a range 1-2 (Steyn 1982). Breeding success is unknown in Namibia but averages 1.0 y/pr/yr in South Africa (Steyn & Grobler 1985).
Threats
There are few threats to this rare species given that the species does not scavenge, occurs in areas away from agriculture and possible persecution, and nests in inaccessible mountain regions in South Africa and Namibia. There is a high certainty that it is overlooked as a breeding species so the breeding populations is probably higher than known or even estimated here. Given that it may have a small population it is subject to vagaries that small populations have in reducing to critically small levels. Inbreeding is unlikely due to migration but Namibia may remain a sink population unless global climate change is responsible for birds starting to breed in southern Africa in the last 100 years. In that case we might expect more birds in Namibia as South African populations expand.
Conservation status
We treat this subspecies as a breeding endemic to Namibia and South Africa for the following reasons. Recent genetic evidence indicates that the southern African breeding form can be distinguished from the larger European birds (a difference of 0.29% of 1041 base pairs) and both body mass and wing length are substantially smaller in southern birds. Named as a subspecies Hieraaetus pennatus minisculus (Yosef et al. 2000), the genus Hieraaetus has recently been subsumed into Aquila (Wink & Sauer-Gürth 2000) and this species thus becomes Aquila pennatus minisculus. Given that there are probably less than 250 individuals and a maximum of about 20 breeding prs in Namibia it is classified as Endangered. There is no evidence of decline per se but fluctuations are expected, and its endemic status and small overall population makes it vulnerable to local extinction.
It has been designated a Specially Protected Species under the draft Parks and Wildlife Management Bill of 2002 in Namibia.
Actions
Determining the size of the breeding populations present in Namibia is a priority. Areas to focus on include the western inselbergs and escarpment, from Brukkaros to Spitkoppe, Brandberg to the Kaokoveld mountains, and to re-examine the Waterberg cliffs for breeding birds. This is best done following high rainfall years. Breeding surveys for Booted Eagles on the Namibian portion of the Orange River beginning in September will also probably yield positive results. Breeding success should then be monitored without disturbing breeding pairs. The discovery of birds breeding between the known distribution in South Africa and Namibia will help determine if this is indeed a contiguous population common to South Africa and Namibia. The protection of new breeding sites will become a priority as they are uncovered.
From: Simmons RE & Brown CJ 2006. Birds to watch in Namibia: red, rare and endemic species. National Biodiversity Programme, Windhoek, Namibia
References
Anderson MD, Maritz AWA, Anderson PC 1995. Booted Eagles breeding north of the Orange River, South Africa. J African Raptor Biology 10: 28-29.
Boshoff AF, Allan DG 1997. Booted Eagle Hieraaetus pennatus In: Harrison JA, Allan DG, Underhill LG, Herremans M, Tree AJ, Parker V, Brown CJ (eds). The Atlas of Southern African Birds. Vol. 1: 184-185. BirdLife South Africa, Johannesburg.
Brooke RK, Martin R, Martin J, Martin E 1980. The Booted Eagle Hieraaetus pennatus as a breeding species in South Africa. Le Gerfaut 70: 297-304.
Brown CJ 1985 Booted Eagles breeding in Namibia Madoqua 14: 189-191.
Brown CJ, Cooper TG 1987.The status of cliff-nesting raptors on the Waterberg, SWA/Namibia Madoqua 15: 243-249.
Brown Chris, personal observation (cb@nnf.org.na)
Jarvis A, Robertson A, Brown CJ, Simmons RE 2001 Namibian avifaunal data base. National Biodiversity Programme, Ministry of Environment & Tourism, Windhoek
Martin RJ 2005. Booted Eagle Aquila pennatus In: Hockey PAR, Dean WRJ, Ryan PG (eds.) Roberts Birds of Southern Africa, 7th ed. Pp 535-536. John Voelcker Bird Book Fund, Black Eagle Publishing, Cape Town.
Pepler D, Martin R, Van Hensbergen HJ 2000 Estimating the breeding population of Booted Eagles in the Cape Province, South Africa. J. Raptor Res. 35:15-19.
Scholtz G 2005. Booted Eagles at Brukkaros crater, southern Namibia Promerops 263:22.
Simmons RE, Allan DG 2002. The Orange River avifauna: abundance, richness and comparisons. Ostrich 73: 92-99.
Simmons RE, Barnard P in press More evidence for breeding Booted Eagles at Brukkaros, Namibia. Gabar
Simmons Robert, Boix-Hinzen Christian personal communication (harrier@botzoo.uct.ac.za).
Steyn P, Grobler JH 1981 Breeding biology of the Booted Eagle in South Africa. Ostrich 52:108-118.
Steyn P, Grobler JH 1985 Supplementary observations on the breeding biology of the Booted Eagle in southern Africa. Ostrich 56:151-156.
Wink M, Sauer-Gürth 2000 Advances in the molecular systematics of African Raptors. In: Chancellor RD, Meyburg B-U (eds). Raptors at Risk, pp 135-147. Hancock House & WWGBP, Berlin.
Yosef R, Verdoorn G, Helbig A, Seibold I 2000 A new subspecies of the Booted Eagle from southern Africa, inferred from biometrics and mitochondrial DNA. In: Chancellor RD & Meyburg B-U (eds). Raptors at Risk, Pp 43-49. WWGBP/Hancock House, UK.