Black Eagle-Africa Black Eagle
Of some 57 species of eagles found worldwide, 17 species occur in Zimbabwe. Thirteen species are considered resident, while Steppe and Lesser Spotted Eagles are Palaearctic migrants, and Wahlberg’s Eagle is an intra-African migrant. Palaearctic migrants breed in Eurasia and north Africa . Booted Eagle is both a Palaearctic and intra-African migrant as there are two distinct populations, the latter race breeding in South Africa. A migrant is one of a massive shift of birds twice each year between breeding and wintering ranges.
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An intra-African migrant is a bird that migrates seasonally within Africa, arriving in Zimbabwe during the austral summer (wet) season and moving north during our winter (dry) season. A Palaearctic migrant is a bird that migrates seasonally from the Palaearctic to Africa during our summer and returning north again during our winter. A nomad is one of an aggregation of birds, including adults, that move irregularly or erratically from one area to another for ecological reasons (usually food and/or water). Consequently a group of juvenile and/or immature birds found away from their natal area would not be considered nomads, as they would be involved in juvenile dispersal. This article introduces a series of vignettes on eagles found in Zimbabwe, starting with the Black Eagle.
Black Eagle One of Africa’s largest eagles (male 3- 4kg, female 4-5kg), the Black Eagle occurs throughout Zimbabwe inhabiting granite inselbergs, sandstone hills, gorges and escarpments. Unusually high concentrations are in the Matobo Hills, containing one of the highest densities of eagle in the world, and up to 60 pairs of black eagles have been found breeding in a 620 square kilometre survey area. Seven pairs have been found breeding along 60km of the Batoka Gorge below Victoria Falls, while some 17 pairs have been found in the Bubiana Conservancy near West Nicholson. Rocky outcrops provide ideal habitat for them and their prey of hyraxes.
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They usually build their large stick nest on a rocky ledge. However, in Zimbabwe it is not unusual for black eagles to nest in trees and this has been recorded at a site near Lake Kariba, Hwange National Park, the south-eastern Lowveld and in the Matobo Hills. Breeding starts in March-April. Normally two eggs are laid, but only one chick survives, as the older “Cain” kills the smaller and younger “Abel” a week after hatching. No satisfactory explanation has been advanced for this behaviour that characterises several other eagles found in the tropics, including Crowned, Tawny and African Hawk Eagles.
In the Matobo Hills, droughts have reduced hyrax numbers by 80% from 1972 to 1992, which has probably caused the 40% reduction in black eagles. Predation pressure on hyraxes has probably increased dramatically as populations of prey and predator have declined disproportionately. This is probably most acute in unprotected Communal Lands, where Black Eagle populations are sparsely distributed, because hyrax
numbers have also declined sharply from hunting (for food, and skins for sale to tourists), and by habitat destruction. However, in the Matobo Hills this trend is being reversed by conservation work by the Ornithological Unit of the Department of National Parks and Wildlife Management, which is monitoring eagles
and running an educational programme in the rural schools.
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The Black Eagles have been studied continuously for 34 years by the Matabeleland Branch of the Ornithological Association of Zimbabwe, amounting to one of the most successful amateur efforts in ornithology worldwide. The programme was led by Val Gargett for 20 years and her monograph on the Black Eagles of the Matobo Hills is regarded as one of the finest accounts ever written on a single species. Despite such intensive research, some fundamental questions remain unanswered, such as; Where do the young birds go? This is being addressed by current research efforts where some juveniles have been fitted with radio transmitters.
