letting nature back in

The crowned eagle, the third largest and the most powerful African eagle, has found a way to survive in close proximity to some urban areas in parts of eastern South Africa.

Key to crowned eagles – who are forest and woodland specialists – being able to live and even breed near urban areas are sufficient patches of indigenous forest in combination with pockets of dense bush and exotic plantations, such as eucalyptus and pine plantations. Not only do such environments provide sufficient habitat for prey animals but they also provide suitably large trees for nesting.

A view from our garden of a section of the neighbouring eucalyptus plantation on the opposite slope. These eucalyptus trees are fast growing and entire compartments are harvested at the same time every few years, so only stray trees that have self-seeded on the margins have a chance to mature into large specimens suitable for eagle nesting sites. Unfortunately, most of the old eucalyptus trees in our neighbourhood have been removed

It is somewhat surprising that such a large eagle has been able to adjust to surviving around built-up environments. Crowned eagles (Stephanoaetus coronatus) are powerful predators and they are able to capture prey that is several times their own weight. The average weight of a crowned eagle is in the region of 3.6 kg (8 lbs), with the female being larger than the male. The broad wings that are short relative to their size and the long broad tail, enable crowned eagles to manoeuvre accurately in between the trees and understorey vegetation in their forest or woodland habitats. Despite the relative shortness of their wings, their wingspan is nevertheless an impressive 1.5–2m on average (about 5–6.5 ft).

In the above photo, a crowned eagle, with its crown of feathers folded flat, shows its camouflaging colouration and its powerful legs and feet equipped with strong talons (the very large hind claws are concealed) for seizing and killing prey. This eagle (the same one as in the header photo) was rescued after being hit by a car. Although its injuries – including a broken wing – healed, it was not fit to fly well enough to be released and it now lives in captivity at the African Bird of Prey Sanctuary near Pietermaritzburg

In our neighbourhood we are most aware of the crowned eagles when they fly overhead calling loudly and repetitively during their aerial territorial or courtship displays. Sometimes we become aware of their presence due to the alarm calls of vervet monkeys and/or the anxious rallying and calling of hadeda ibisis – both species preyed upon by crowned eagles.

A pair of crowned eagles in aerial display above our garden

I do not know where this pair of crowned eagles is nesting, but I hope their nesting tree is safe from being felled.  As I mentioned in last week’s post on long-crested eagles, I have posted about the black sparrowhawks that used to nest behind our house who were displaced by the felling of old eucalyptus trees despite their specific nesting tree being saved.

In a study of breeding pairs of crowned eagles, which included the greater Durban and Pietermaritzburg areas (MacPherson 2015), it was found that mature eucalyptus trees were the favoured nesting trees of crowned eagles in this region. However, an ongoing initiative to remove these invasive and water-thirsty exotic trees has seen the removal or ringbarking even of actively used nesting trees of crowned eagles and black sparrowhawks (p.33). Where such trees provide raptor nesting sites in the absence of any alternatives, it would seem that such removal policies need rethinking. For example, as suggested by MacPherson, stands of mature eucalyptus trees could be under-planted with suitable indigenous tree species to replace the eucalyptus trees and restore forest patches over time (p.34).

Unfortunately, all but one of these older eucalyptus trees that used to grow on slopes between the residential area and the plantation have been felled. On the opposite slope (from where this photo was taken) is the start of the eucalyptus plantation where the trees are clear cut when at harvesting age

Adult crowned eagles form monogamous breeding pairs and they are known to return to the same nest year after year. Depending on factors such as habitat, food resources and climate conditions, in some regions they breed every two years and in others they breed annually, which is the case in the Durban area (MacPherson, 2015).

Crowned eagles lay two eggs but only raise one chick (the older chick is programmed to kill the younger chick). The developmental process is long and a youngster is dependent on being provided with food by the parents until it is 7 to 12 months old. It then has to depart and make its own way in the world.

Juvenile crowned eagles are very different in appearance from adults – they are much paler with the head and underparts being creamy white. The wings and upper-parts are a brownish-grey with a faint barring on the feathers that are outlined in creamy white creating a scalloped look. The tail is barred as in the adult.

The first two years of life for a juvenile crowned eagle are particularly difficult and many do not survive. Crowned eagle sub-adults reach breeding-age maturity when they are 4–6 years old.  

About two years ago I photographed a pair of nesting crowned eagles in the rural Mpushini Valley. As can be seen by the density of sticks this nest has been in use for some years. One of the parents is at the nest rearranging nesting material at the commencement of the breeding season

The study of crowned eagles in the Durban, Pietermaritzburg and adjacent regions in KwaZulu-Natal included placing cameras at nests in order to ascertain what prey animals were brought to the nest (MacPherson 2015). In most prior studies bones found at the base of nesting trees were a primary means of determining prey animals. The advantage of using cameras at nests is that they  were able to show soft-boned prey animals brought to the nest, such as fledgling birds, which would be consumed completely leaving no remains to be found beneath the nest.

From the prey items identified in the study (a total of 836 items), rock hyrax (42.2%) were in the majority with hadeda ibis second (19.4%), and of these 89% were young birds not yet able to fly. Next in order, were blue duiker and vervet monkey. Other prey items included grey duiker, one bushbuck, and small mammals such as mongooses. Very few domestic animals were brought to the nest. There were several chickens (3.3%), 7 domestic cats (pets or feral) comprising 0.8% of the total, and no dogs.

After having witnessed in our neighbourhood what appeared to be an ongoing war between Egyptian geese harassing the black sparrowhawks when they were actively nesting – Egyptian geese are known to takeover abandoned or disused raptor nests –  I was fascinated to read in the MacPherson study that the camera at one nesting site showed that a breeding pair of Egyptian geese moved into a crowned eagle nest already accommodating a young crowned eagle fledgling and cohabited in the same nest (MacPherson 2015: 104). 

A hadeda ibis fledgling, favoured prey of crowned eagles, perched in its rather scraggy-looking platform nest alongside its parent. The nest was in a tree in our neighbour’s garden above our fence line and I took this photo from our garden

It is known that small pet dogs (and pet cats) have been taken by crowned eagles from their owners gardens, but in most cases such pets are taken by juvenile eagles who are inexperienced hunters, and mostly during the months of winter when times are hard. The instances of pets taken by crowned eagles are of course most distressing, but proportionally the numbers are small, not that that is of any comfort to anyone losing a precious pet.

We think one of our beloved cats was killed and then for some reason abandoned by a crowned eagle in our garden. Perhaps it was disturbed by our two dogs. Although we cannot be certain, we think the cat was most likely killed by an eagle because of the nature of the puncture injuries at the back of the cat’s neck and spine. (Distressingly, those same dogs did kill a visiting cat that strayed into our garden, but that cat died from crush injuries and from being shaken with no visible punctures or openings in the skin.)

Since the killing of our cat fifteen years ago, and for other reasons too, our cats now have outdoor access from the house to an enclosed garden. Not only does it keep them safe from hazards that include predators, cat fights and vehicles, it importantly also curtails the cats’ opportunities for recreational hunting. Although I was completely devastated by the killing of our cat, I believe that it is our responsibility to devise ways to live as harmoniously as possible with wildlife, including when wild animals and birds find ways of surviving in suburban areas.

I was alerted by hadedas raising the alarm to the presence of this crowned eagle, perched in the eucalyptus tree (abandoned by the black sparrowhawks) outside our garden from where it surveyed the plantation. Like most crowned eagles, this bird was not only alert but extremely wary so I had to stay as concealed as possible and at a considerable distance as I took this photo from near our house

Crowned eagles most commonly use an ambush-style of hunting. They patiently wait perched up in a tree in the forest or woodland usually above a known nature path and drop down from their perch onto a prey animal passing underneath. The prey is killed on the ground. An animal that is too large to lift whole will be dismembered and parts delivered to the nest or taken away in sections to be stashed or eaten.

Crowned eagles do also hunt on the wing and hunting may be done by a pair working in cooperation with one flushing the prey, for example monkeys, with the other one following up to catch an animal or bird as it flees.

A few months ago I heard a crowned eagle calling repeatedly from nearby. I went outside with my camera to discover a vervet monkey alarm-calling from the edge of the plantation while watching the crowned eagle that was perched in a nearby tall tree, concealed from my view by another large tree in between.

I recorded the calling of the unseen crowned eagle by taking a video showing the foliage of the intervening tree, and then I crept down to the back fence and filmed the very agitated vervet monkey sounding the alarm. When I tried to peek round the vegetation to get a view of the eagle it flew away – I think I frightened it off. After the eagle’s departure one monkey ascended into a tree to assume a lookout role while some youngsters broke cover to play and forage in the relative safety of a dense stand of (alien and invasive) lantana and Mauritius thorn. Although a bit snippety as I had no idea what was going to happen next as it unfolded, the video I captured is below.

In the IUCN Red List the crowned eagle is classed as Near Threatened with the population decreasing. Crowned eagles occur in forested and woodland areas over much of central Africa and also down the southern eastern side of the continent into South Africa. Threats to crowned eagles include deforestation where forests are depleted or destroyed to provide or make way for timber, agriculture, palm oil trees, charcoal and mining, for example, and in some regions crowned eagles are deliberately targeted to be killed where they are seen as competing for bush meat.

In the study on crowned eagles undertaken in KwaZulu-Natal, in addition to habitat destruction that includes deforestation and the felling of nesting trees, threats to crowned eagles that resulted in the deaths of crowned eagles in the study area included collisions with vehicles and barriers such as walls, wire fences and window panes, as well as deaths caused by gunshot wounds and electrocution. These factors caused 80% of the deaths of crowned eagles recorded in this study. Other causes of death included harassment by people or pets and one case of poisoning (MacPherson 2015, p.81). Work is ongoing with the providers of electricity to insulate and design more bird-friendly installations, and ongoing citizen-science initiatives are intended to raise public awareness and participation in the protection and management of urban wildlife species.

I do not have a photograph of a crowned eagle raising its double crest that forms a crown of feathers when erect. However, in this photo the white tips of the crest feathers on the top of the head are visible even when the crest is lying flat

We are fortunate to live in a region with a mosaic of different vegetation types and land usages, an environment that enables a diversity of vegetation and animal and birdlife to survive. It is to be hoped that despite the ongoing development of “urban sprawl” this variety can be maintained. And just as some wildlife species are finding ways of adapting to people, so too it is to be hoped that more and more people are prepared to find ways to adapt to and accommodate wildlife in their midst.

 References:

BirdLife International. 2018. Crowned Eagle Stephanoaetus coronatus . The IUCN Red List of Threatened Species 2018.  https://www.iucnredlist.org/species/22696201/129914678;  Chittenden, Hugh, Davies, Greg & Weiersbye, Ingrid. 2016. Roberts Bird Guide: Illustrating nearly 1,000 Species in Southern Africa (2^nd edition). Cape Town: Jacana;  McPherson, Shane C. 2015.  Urban Ecology of the Crowned Eagle Stephanoaetus coronatus in KwaZulu-Natal, South Africa. PhD dissertation. Pietermaritzburg: University of KwaZulu-Natal. https://pdfs.semanticscholar.org/d3de/c417ed8e547ecca352cf32fa0cb22e30fba0.pdf;  McPherson, Shane. [n.d.] Crowned Eagles in the Big City.  The Leopard’s Echo. https://le.kloofconservancy.org.za/crowned-eagles-in-the-big-city/;  Wikipedia. 2020. Crowned Eagle. https://en.wikipedia.org/wiki/Crowned_eagle

Posted by Carol