History

Klipriviersberg Ridge System (KRS)

For many years and dating back to the late 1950’s, sightings of predominantly individual and occasionally a pair of Verreaux’s eagles have been reported to skirt the ridges and sporadically hunt on the bountiful Rock hyrax (Procavia capensis) commonly referred to as dassie, littering the entire ridge system and found to occupy medium to large colonies.

During 1997, I followed up on some leads pertaining to a possible nesting site within a large eucalypt tree that was situated on an old homestead that has subsequently been incorporated into the greater Klipriviersberg Nature Reserve, but no evidence thereof could be established. During the same year and over a three-month period, just on weekends, we walked the entire ridge system starting from the eastern ridge end at the R59 (Sybrand van Niekerk freeway) and ending on the outskirts of Eikenhof/Naturena close to the N1 Highway in the west. The bulk of our investigation was spent looking for possible nesting sites within the granite boulder-strewn outcrops and ridges that lay scattered along the length and breadth of the approx. 14km ridge system. Apart from the thousands upon thousands of hyrax colonies found in just about every nook and cranny imaginable, the more modernised sites such as storm water pipes / gullies and culverts, illegal rubble dump sites, municipal water reservoir infilling sites inclusive of private garden refuse heaps are all ideally suited for hyrax friendly infiltration abodes. Despite the lengthy criss-crossing of the ridges, we only located two possible sites of which one was above the suburb of Mondeor and the other on Meyer’s Farm close to the Comaro Road slipway off N12 Southern Bypass on the western boundary of the farm. Both sites had a scattering of sticks on rather small ledges of flat outcrop – to my knowledge, too small to occupy a substantial nest over a longer time period. Among the sticks were some bone fragments and the tell-tale evidence of very old and fragmented hyrax skulls and toothless jaw bones. The possibility exists that eagles may have bred there previously, but it would be difficult to determine the age of these sites, which could only be executed via DNA testing, albeit costly, to determine the age of the bone fragments.        

Suikerbosrand Nature Reserve (SNR)

For as long as I can remember, there was always a Verreaux’s Eagle pair nesting on a rocky cliff on the south-eastern slopes of the Suikerbosrand Nature Reserve (SNR). Many raptorphiles, birders and bird club members alike, mentioned the eagles flying overhead, perching on rocks and in trees, as well as seeing them incubating the eggs and chicks growing to juvenile and fledging stages…by far a highlight should you visit the reserve and see them!

Prey should be well stocked for an eagle pair to take up residence in the vast reserve and having telephonically spoken to Heidelberg municipality staff, folk working at the Heidelberg Rekord newspaper and some estate agents, all were in agreement that they were very proud custodians of “their” Black eagles! Prey such as hyrax are in abundance and not deemed to be in limited supply as during the winter months dozens were seen sunning themselves huddling together on rocky outcrops. Apart from hyrax there is good stock of alternative prey such as rock rabbit, scrub hare, guineafowl and francolin, not to mention the occasional monkey troops flitting by…wary and hurriedly!

So, what happened during 2003 when the eagles vacated their nesting site for no apparent reason? As mentioned, there is abundant prey…no interference reported seen nearby, at or on the nest…yet they just upped and left.

It is quite possible that the pair was harassed on or off the nest by baboons, leopard, humans and or a caracal…the latter possibly stands little chance against a formidable pair of eagles with super sharp talons, but it may have taken their chick or juvenile whilst they weren’t in attendance – similarly occurred at Roodekrans during the double clutch breeding season of 1996, when a caracal killed the three-month-old juvenile and thereafter the carcass was entirely dismembered by jackal. Sometimes eagles may feel threatened by predators and as I have witnessed baboons harassing an eagle pair on a farm outside Bela Bela and similarly at Roodekrans, and the aggressive alarm calls by the eagles were possibly enough of a deterrent to chase off the caracal and baboons. However, eagles stand a slight chance fending off a leopard and even a much lesser chance if humans were to destroy the nest and or steal the eggs or a chick! The eagles will defend their offspring at all costs as was witnessed at Meyers Farm when Brett Gardener tried to get to the chick on the nest. Taking the eggs or a chick can thus never be excluded as humans do these things mainly for collection purposes or to raise a pet. During such occasions it is quite possible that the eagles lost their fight against the odds and once “too harassed” they will vacate such a site and move elsewhere knowing that their trusted nesting site offers no protection.

This is a very large eagle. The adult is pitch black with a white ‘V’ on its back and white on the rump. The female has solid white on the back and rump, while the male has the white of its back and rump separated by black feathering. The bill is black, the cere and feet are yellow. White ‘windows’ in the wings are a prominent feature of this species. The wings are broad, narrowing towards body. The juvenile is a mottled golden dark brown with black blotches. The nape and crown are golden brown. The immature bird begins to develop white on its back and rump well into the second year of its life.

General Characteristics of Eagles

The word “raptor” comes from the Latin raptare, which means ‘to seize’. Raptors therefore have clasping talons and hooked beaks with which to catch and tear their prey. There are a total of 84 raptor species in South Africa of which 12 are owls and 9 vultures. Some scientists argue that vultures are not really raptors, as their talons are not very powerful and they do not seize their prey in true raptor style, instead eating carrion and relying on their powerful beaks to tear meat and crush small bones.

Depending on conditions, adult eagles may live for 20 to 30 years, and in common with most long-lived animals have very slow breeding rates and an extremely high incidence of mortality among young birds. On average, only 30% of young eagles survive their first year, and only half of these eventually reach maturity. This situation is acceptable provided the adult survival rate remains high. If the balance is disturbed by unnatural mortality factors such as poisoning or shooting, the population may exhibit a drastic decline or even become extinct.

Distribution

The Black Eagle is limited to mountain ranges and rocky outcrops throughout Africa (from south to north), but young birds may wander widely. The distribution of these birds closely correlates with that of the Rock Hyrax, its favourite prey. Territory size is determined by prey availability and topography.

Breeding

Black Eagles are monogamous. The nest is built on cliff ledges and may be used for many years. Within the pair’s territory a number of nest sites may be selected, but one being favoured. They are territorial, so will not tolerate other Black Eagles nesting or passing through their territory. Courtship consists of spectacular flights where both birds fall and climb for hundreds of metres. They frequently drop a stick, especially the male, and then stoop and roll onto their backs to catch it.

Feeding & Hunting

Rock Hyrax  or dassie make up at least 90% of their preferred prey with the male and female often hunting cooperatively with one bird making it obvious to the prey while the other stoops and veers around rocks to surprise the unsuspecting victim. Black Eagles will also hunt guineafowl, francolin, rock rabbit, scrub hare, mongoose and carrion.

Nest building

The nest is built by both the male and female and consists of a platform of large sticks. The cup is lined with green leaves. Old nests can be 2.5m in diameter. The nest is almost always on a steep, inaccessible cliff, but very rarely also in a tree. Two plain white or blotched eggs are laid from April to July (mid-winter) and are approximately 66.7-86.0 x 52.0-62.0 mm in size. Incubation is about 45 days and chicks take about 2 days to hatch. Ninety-nine percent of the time only one chick survives due to the “Cain and Abel” struggle where the stronger (usually older) sibling kills the weaker. The surviving youngster will fledge at about 13 weeks. Once hatched, the nestling spends 3 months in the nest before being able to fly and post fledging will remain dependant on the adults for an additional 3 months when it will be forced out of the territory by both adult eagles. The young bird goes through various stages in plumage growth and reaches adulthood over a period of 3 to 5 years.