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Verreaux’s eagles’ breeding

Verreaux’s eagles’ breeding

Egg Laying

Usually, in the “wild” eggs are laid from late April to June with a peak in May and only occasionally in July. In an urban environment, eggs are usually laid at least a month sooner, by about end March to early April. It is not known why urban eagles lay sooner but over many years of observing the Roodekrans, Wonderboom and ANP pairs, this trio lay within weeks of another, occasionally within days.

Incubation

Two eggs are normally laid and three-egg clutches have been recorded at Roodekrans and Wonderboom with the latter fairly frequently as do some pairs in the South-western Cape.  First eggs are always larger, and in some clutches there is a considerable difference in the sizes. Eggs are laid three to four days apart, usually four, and although first-laid eggs may not be incubated on the day they are laid, but at the ANP, incubation commences immediately. During incubation, the eggs are brooded about 92% of the daylight time, with both male and female doing a share, his normally when he brings prey for the female and she leaves the nest to feed on it. During the incubation period, food is never brought to the nest. The female sits overnight, and the male’s share is during daylight varies from pair to pair and at the ANP, the female always sits overnight with the male roosting in a tree fairly nearby.

Hatching

An egg takes about two to three days to hatch from the time when the first cracks in the shell appear, but before this the chick can be heard cheeping inside the shell. Eggshells are not removed, breaking into fragments that disappear under the nest lining. When the second egg hatches three to four days later, the first chick has already developed its coordination.

Sibling Aggression

A period of relentless sibling aggression occurs during which the first-hatched chick pecks its sibling until it dies from a combination of its injuries and starvation.  As soon as the second egg hatches and the chick starts to move about, it is attacked by its older sibling, who adopts a trucelent posture with chest forward and downy wing stubs held out. Twisting downward pecks are delivered, mainly to the head and back, stimulated by any movement from the second chick. When it tries to come forward to feed, the first chick will attack it. The female makes no attempt to intervene in any way; the attacks may even continue beneath her breast feathers while she is brooding. Gradually the second chick becomes weaker, loses weight, and no longer has the strength to try to feed and succumbs.

Growth Chick

The newly hatched chick is covered in fine white down; the cere and feet are flesh pink, the eyes black and the bill is horn coloured. During its first four weeks the nestling grows rapidly, acquiring a much thicker coat of white down through which first feathers are just appearing along the hind edge of the wings; the cere and feet are yellow at this age. 

The feeble newly hatched chick may receive its first meal when only three hours old. During its first few days its coordination develops rapidly until at the age of four days it can direct accurate pecks at its sibling. Chicks in exposed or sheltered nests would require different amounts of care. The overall picture is clear, in the first few days a parent is on the nest about 98% of the time, and the chick is brooded a great deal; the male assists in this, but his share is small, and his main function is to bring prey, which he provides well in excess of the immediate requirements of the female and the chick. During the first month a parent is at the nest 85-95% of the time. 

Eaglet

At five weeks feathers are breaking on the scapulars and wing coverts, and first tail feathers appear. From six weeks on, it develops very rapidly until feathers cover the down at the age of eight weeks.  It first stands when about a month old, and tries unsuccessfully to feed itself, which it can only achieve at the age of six weeks. However, because of the tough nature of its staple diet, the female continues to tear open carcasses, as well as to feed it, until end of the nestling period. Although it attempts some wing flaps as early as two weeks, proper wing exercises only take place once it is feathered, increasing in frequency at the end of the nestling period. In the second stage, the female leaves the eaglet alone for progressively longer periods. Even in the exposed site it no longer needs shading, once it is about six weeks old. The female now also hunts actively, and continues to tear up prey for her offspring. The adults bring in birds plucked and hyraxes partially plucked. The nest is kept clean by the removal of bones and dry pieces of skin, and both sexes bring fresh lining, although not after two months. During the second month, a parent may be at the nest 50-55% of the time.

Juvenile   

Parental attention in the nestling period is linked to three main stages of the eaglet’s development, which may be divided into its downy first month, the second month during which it becomes fully feathered, and the third period up to the time of its first flight. In the final stage parental time on the nest is mainly spent in delivering prey. During the third and final month, a parent may be at the nest for 10-15% of the time.

Fledging

The juvenile first flies when between 90 and 98 days old, although it can leave the nest at 80 days if disturbed. Extensive personal observation is indicative that males usually fledge between 90-95 days whilst the heavier female fledges between 95-100 days occasionally observed fledging on 104 days. Males may however fledge sooner as was the case with “Witsie” who fledged at 86 days.  Males are smaller and lighter by weight than the females.

Its first flight is usually made independent of the adults’ presence; one flew 80m to an outcrop where it remained perched for a very long period of time. In its first month the juvenile is not adept at flying, in fact, it flies very little, spending much of its time on the nest where it roosts or on nearby perches and rocky outcrops. 

In its second month it becomes more accomplished on the wing and more adventurous, exploring and expanding its range, as well as occasionally accompanying its parents for short distances. At night it continues to roost on the nest.

During its third month out of the nest the juvenile wanders further afield, often well out of sight of the nest. It begins to snatch up items such as a spray of leaves and flying with it in its talons; this behaviour is linked to its increasing dexterity on the wing and serves as mock killing practice. It rarely visits the nest in daytime, although roosting on the nest or on perches in the area. Towards the end of the post-nestling period of three months the parents begin to chase it away.  

Post Fledging  

Throughout the post-nestling period the juvenile is fed regularly by the adults, and can always be located by its noisy cries of solicitation whenever it sees them. During the first month prey is brought to the nest, after which it’s normally delivered at various other perches, although the juvenile may still carry the prey to the nest and feed on it there. If it does not finish a meal, the female will feed on what is left, but the young bird is fed preferentially. It flies about very little with its parents, never accompanying them on hunting flights, and by the time it leaves the territory has yet to hunt and kill for itself.  In one study it was estimated that the adults and their eaglet accounted for about 236 hyraxes from hatching until the independence of the juvenile after a thirteen-week post-nestling period.

Once driven out of the territory the juveniles wander, or are harried by neighbouring pairs, until they reach a peripheral neutral zone or “empty quarter”, juveniles also group together and are referred to as floaters. . Ringed juveniles have been recovered at distances of 40, 72 and 176 km from their nest sites during the first year. 

Some of the predators on Verreaux’s eagle nestlings are baboons, crows, possibly pythons, leopards, caracal and small predatory mammals such as genets. 

As only a low 20-30% of the juveniles survive during their first year, mortality is a major cause in the demise of young birds of prey and includes:

  • Inability to hunt successfully,
  • Drowning in partially full/empty farm dam reservoirs,
  • Scavenging on poisoned carcasses,
  • Feeding on road kills and run over by truckers,
  • Colliding with overhead power cables maiming or be killed outright.

 

  • Basic Breeding Information

    A breeding season can be categorized into seven stages: 

    Nest refurbishment /Mating – March/April

    Egg laying – April/May

    Incubation – 44/5/6 days, April to June

    Hatching & Sibling Aggression – up to 7 days

    Nestling – 86 to 100 days, September

    Fledging – August/September 

    Ousting November/December  

    It is of utmost importance that your observations of the eagle’s crops, and prey status is correct at all times.

    Prey variation may consist of hyrax, red rock rabbit, scrub hare, guinea fowl, francolin, mongoose and the occasional monkey.  

    NB – the eagles do not prey on domestic dogs, cats and chickens. Any person who conveys this kind of information to anyone will be severely reprimanded as it may be detrimental to the eagles’ livelihood!!

     

Verreaux’s eagles’ nest sites

Verreaux’s eagles’ nest sites

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

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. 

Nest Building

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.

Leafy Sprays

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.