Generally nest sites are in inaccessible habitat, has ensured that this eagle, though often persecuted by farmers, has most recently shown a steady decline in areas where previously pairs were observed to be frequent visitors. Throughout its range it occurs in rocky or mountainous terrain, but the environment may vary from semi-arid to areas of high rainfall.
Over the years, nests have also been constructed in large trees such as eucalypt spp and pine spp as well as a baobab, on the ground, in power pylons and concrete microwave towers even on top of the telephone pole nests of sociable weavers. Invariably, its presence almost always coincides with that of its principle prey, the hyrax.
At MF, the ANP is the first known of nesting site purposely designed and constructed for this eagle species and as far as we are aware, it is a first for Africa. Not ideal in any way, as it offers no natural shade during the incubation period and when there is a chick growing up to juvenile stages, but during these instances, the female will provide shade on hot days. During the shade offering period and especially on hot windless days, one will observe that the adult/chick/juvenile is panting, with its beak slightly open; they will let air flow over their tongue to allow salivation to occur.
Courtship displays are similar to the territorial displays performed throughout the year and are done singly or by the pair. Spectacular, steep, undulating dives are executed. At the top of the upward swoop the bird turns sideways or somersaults and rolls into the next dive with wings held against the body. On the upward swoop, and during the turn at the top, the white back shows conspicuously as the wings are opened. In a different display performed exclusively for courtship the male flies behind the female with his wings curved up above his back in a more exaggerated position than during normal soaring; he draws near her she may half roll and present her claws. Tumbling flights with interlocked claws are probably not a part of courtship and may be instances of occasional aggressive interactions with intruders.
Mating usually takes place on a favourite branch or rock perch near the nest, to the accompaniment of calling and rustling of feathers soon after. Mating may last between four and twenty-one seconds and can be performed 3 to 4 times per morning.
Building a new nest from scratch may take an adult pair anything between six to eight weeks and such an activity will commence in early February and be complete by at least end March should they want to breed in that year. Once eagles have begun building, there is little chance in stopping them as they are on a mission to complete the structure and be certain that it is secure and that it will withstand the prevailing elements. Building a nest on a sturdy base such as a flat rock surface and or a platform such as the ANP, the chances of structural failure is greatly reduced, whereas building a nest in a tree is far more difficult as the supportive structure beneath the nest will have to carry the increased weight load of annual nest refurbishment.
Structural strength and stability thus play a large role in successful breeding and although some nests may increase to in excess of 4m tall, it will become precarious over time and it may topple over with a possible loss of life and or permanent injury to the birds. At Roodekrans during the no breeding event of 2016, during a heavy storm and high wind spell, the nest height was reduced by about 2m in height, which equates to about 4 to 6 years of bygone breeding seasons, quite a substantial amount of lost material.
At the old pylon nest, the structure was and still is incredibly secure hence the fact that the eagles decided to build their nest within the first tier. By no means a safe site considering that 210KV of electricity passes in one end, is then bridged by very heavy cabling that projects 5m from the pylon under which the eagles fly to alight the nest…a very precarious and dangerous past time especially for young inexperienced juveniles to fledge and alight from.
In 2009, whilst the ANP lay on the ground in two segments, Philip Tarboton, Teresa Moore and I built a new nest for the eagles that only took us two hours to construct complete with nesting cup that was lined with green leafy sprays, and tied to the basket structure with cable ties to prevent it disintegrating upon hoisting. When the eagles eventually took to –and liked the new nest, they brought additional nesting material to suit them and their comfort and whilst Teresa and I observed almost 12 hours 7 days per week!
We did notice that there was quite a sway in the mast and that the nest moved at least 15-25cm from side to side…enough to cause me considerable dizziness. Long story shortened, the breeding season was unsuccessful and both eggs addled, with the female aborting incubation after sixty days.
Unfortunately we could not retrieve the eggs in time so that we could send them to Onderstepoort Veterinary School for an autopsy; the crows had already gotten to the eggs eating the contents thereof. Devastated, but willing to understand and learn from the failure, we had a meeting with Toni Niemand of Siyavaya Highway Construction JV and requested that the group add a cat ladder to the mast in an effort to stabilize the movement. Fortunately, the JV agreed to our proposal and by end February 2010 the contraption was lifted with a cherry picker and bolted to the mast with a specialist fixing bracket. The sheer weight of the additional 1.5 ton structure secured the mast adequately and we were finished just in time for the eagles’ return and their commencement of refurbishing the nest. Equally delighted that the eagles decided to return to the ANP and not rebuild the pylon nest, was immensely appreciated and we believed that they were showing us their appreciation for our consideration in a combined effort to secure their nesting site from swaying and unwarranted intruders.
After the completion of stick refurbishment, green leafy sprays are brought to the nest to soften and line the 30-40cm round cup and if the eagles are going to spend 44 or 46 days incubating, they may as well be comfortable! Repair of an established nest takes about one month. Sprays brought to the nest sporadically by both sexes, frequently when relieving the partner at the nest. It is believed that apart from the comfort of using leafy sprays is that some species may inhibit medicinal values that reduce bugs and flies on the nest. At the ANP most sprays is from the rhus spp. whilst eucalypt and cabbage tree leaves are also used.