Territorial Boundaries of the Roodekrans Black Eagles
Aims & Objectives
- Establish the extent of the territorial boundaries of the Roodekrans Verreaux’s (Black) Eagles Aquila verreauxii,
- Study birds of prey biology at their nesting sites within their greater hunting territory,
- Assess prey availability, its variation and decline,
- Monitor encroaching development and the loss of natural hunting habitat,
- Facilitate farming community and suburban education and awareness programs.
On an ad hoc basis, monitoring of the eagles began in the mid 1980’s by enthusiastic members of the public. In 1988 it progressed to become a school project led by Albert Froneman and during 1992 Albert and friends Chris van Rooyen, Rob Harrison-White and Sally Panos founded the Black Eagle Monitoring Group. In 1996 it became renamed to the Black Eagle Project Roodekrans (BEPR) and subsequently became a non-profit organisation.
Situated within the most magnificent setting of the world renowned Walter Sisulu National Botanical Garden in Roodepoort, Gauteng Province, South Africa, and at that time, there was only two known of eagle pairs breeding within an urban environment with the other pair resident at the Wonderboom Nature Reserve in Pretoria.
The aims of the BEPR are:
- To educate and inform the public about Black Eagles and raptors in general,
- To conserve and secure the Black Eagles in the Walter Sisulu National Botanical Garden for future generations to enjoy,
- To observe and gain information on their breeding behaviour.
In 1996, Black Eagle Monitoring Project parted company with the EWT’s Raptor Conservation Group and became affiliated to the Walter Sisulu National Botanical Garden. The project was renamed the Black Eagle Project Roodekrans and registered as a Section 21, non-profit organisation, with its own constitution, banking accounts and appointed auditor. The project consists of a 7-member committee and approximately 30 dedicated volunteer members.
Comprising almost 300 ha in extent, it has a restaurant, gift shop and nursery that sell indigenous plants.
Eagle presence date back to the late 1930’s when occasional sightings were made of eagles flying along the ridges not too distant from their nesting site. During that era, the eagles may have occupied a home range (territory) of approx. 10-15 km² which is the norm for Black Eagles in general. However, when the botanical garden became established in 1982, so too did residential and commercial development increase and from 2000 to mid-2003 we conducted a territorial study and it was established that their boundaries had increased to approx. 250 km² which is abnormal and incredibly large for an eagle pair with their northerly and furthermost boundary extending 15 km from their nest site!
During the 1990’s, and through close observations, it became apparent that there existed a severe natural prey shortage as by then development had already decimated most of their nearby hunting habitat thereby forcing the eagles to hunt further afield and over great distances. The eagles’ behavioural patterns became altered towards one another and frequent fighting between the pair became noted. In consultation with birds of prey specialists, it was determined that the eagles’ anxiety originated from their inability to hunt successfully in the shortest possible time frame, especially during their winter breeding season when there is a chick on the nest. During our consultations, it was agreed upon that artificial supplementation should be administered on a scientific basis and strictly administered.
January 2000 – July 2003
Blue border constitutes 200 – 250sq.km.
Highlighted – approx. 75% of total area.
Districts covered during 2001/ 02/03
- Roodekrans, Ruimsig, Little Falls Ridge & Kloofendal.
- Krugersdorp North.
- Krugersdorp Game Reserve.
- Rhino & Lion Game Reserve.
- Zwartkop & Tweefontein.
- Kromdraai Conservancy.
- Rietvlei Agricultural Holdings.
- Honeydew Agricultural Holdings.
Trade-offs in conservation today are a reality, particularly at the interface where humans and the natural environment meet. It is therefore not surprising that natural areas, parks, and delineated green spaces in urban areas will face threats from further development. Justifying the maintenance of these spaces therefore remains a challenge (Chiesura 2004). The Walter Sisulu National Botanical Gardens at Roodekrans are a suitable example of an oasis in a sea of development. Developments spring up every month around this green space and still Verreaux’s Eagles persist in the area. Furthermore, they continue to breed, as they have for the past few decades (Symes and Kruger 2012). And when we erect towers to encourage breeding they move in, like at the Klipriviersberg Nature Reserve (van der Lecq 2013).
These records are encouraging and represent the consistent work of a number of dedicated individuals that ensure the protection of these birds.
Once again these two pairs have initiated breeding in 2014 and details on their progress are summarised below.
Table 1. Breeding details for breeding Verreaux’s Eagles at the Walter Sisulu National Botanical Gardens, Roodepoort, and Meyer’s Farm, Klipriviersberg, Alberton during 2014.
|1st egg laid||30 April||8 May|
|2nd egg laid||4 May||12 May|
44 days incubation
44 days incubation
44 days incubation
44 days incubation
|Cainism||Ended 22 June||Ended 27 June|
|Fledgling period||Approx. 15 September (95 days)||Approx. 22 September (95 days)|
The most humane method to obtain rabbit carcasses was to purchase from commercial breeders that bred specifically for the meat market. The only difference was that our rabbits were intact with fur coats and intestines. Most importantly was that the fur had to match those of rock rabbits and hares that breed within the rocky ridges. One defrosted and disease-free carcass was supplemented only when prey stress prevailed and at most only one item per week.
Over the many years of my involvement and having spent at least 90% of my free time observing the eagles’ behaviour and breeding biology, we came to understand how they hunted, how frequent, how long, what was hunted and was the prey adequate to feed both adults and a growing chick to adulthood. However and fortunately, the eagles’ most preferred prey in Rock Hyrax improved from 2003 onwards and it had become unnecessary to supplement artificially. Alternative prey hunted by the eagles includes guineafowl, francolin, hare, rock rabbit and mongoose.
Interesting observations on Roodekrans pair
No sibling aggression was evident soon after the hatching of the 2nd chick and for 3 days the female fed both nestlings. This phenomenon was short-lived and aggression commenced on Friday 20 June and ended by noon on Sunday 24 June. Incubation was not proportionally shared with the female contributing approximately 80% and the male contributing only 20%. A variety of prey items were recorded being returned to the nest on virtually a daily basis. On four accounts the male only fed himself and did not offer anything to the female. This resulted in some aggression towards the male. Important prey has included hyrax, guineafowl, rock rabbit, scrub hare, francolin, and mongoose.
Interesting observations on Klipriviersberg pair
Ample prey items have been observed on the nest in the form of rock hyrax, rock rabbit, and guinea fowl.
Natural prey variation between the Roodepoort and Alberton nesting sites.
For a considerable period of time, at least three to four decades ago, the once abundant rock hyrax populations have dwindled vastly and are poorly represented within the greater home range of the Roodepoort pair. Hyrax that should under ideal conditions make up about 90% of a pairs’ prey, in this urban setting, currently features a lowly 20-30% by comparison. Guineafowl, francolin, mongoose, red rock rabbit, and scrub hare make up the bulk of prey items caught. From 2002-2007 (during the winter weekend months from April/May to August/September) the Hyrax Operation Project under leadership of Boudewijn van der Lecq, Teresa Moore, and Dennis Dry successfully captured and reintroduced approximately 800 live hyraxes from two urban nature reserves, four private residences and one residential estate into suitable habitat within the eagles’ immediate and extended home range. The availability of 12 localities within six ideally suited hyrax-friendly habitats were investigated of which currently three sites yet remain active and self-sustainable. The bulk of the hyraxes that are caught by the eagles are largely from previously reintroduced populations.
The entire Klipriviersberg range that extends approximately 15km from Alberton in the east to the Golden Highway in the west, south of the N12 freeway, is largely a hyrax stronghold much to the dislike of residential estate owners, freestanding residences and townhouse dwellers. North of the N12 freeway in the suburb of South Hills, there are strongholds of 3,000-5,000 hyraxes that live within the granite koppies and storm water pipes. Many are snared by vagrants that live within the ridges. During a ridge walk that was conducted by BKvdL in 1997, a population of 20,000-25,000 individuals was estimated for the region. Within the immediate ridge area where the Siyvaya Artificial Nesting Platform (SANP) stands erected, there are approximately 5,000-7,000 hyraxes within 10km². These hyraxes make up at least 97% of this eagle pairs’ prey base. The remaining 3% of prey includes rock rabbit, scrub hare, guineafowl, and the occasional vervet monkey.
The distance between the two nesting sites is approximately 32km and although no suited cliff face nest sites exist along the entire Klipriviersberg range, previous research is indicative that this range could ideally support at least three pairs of Verreaux’s eagles using ANP’s as nesting sites.
3 DAYS OLD
CAIN & ABEL
I left the BEPR in 1999 to focus upon our research to determine this eagle pairs’ territorial boundaries which took from 2000 to mid-2003 to complete thanks to farmer and small holder property owners support and our extensive study field notes.
From 2003 to 2008 we embarked on yet another extensive research project where we captured and reintroduced Rock Hyrax to naturally supplement the eagles’ prey base with their most preferred prey – I re-joined the BEPR in 2007 to 2015 mainly as an advisor to the project.
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