February 2008

An investigative survey was conducted at Little Falls Extension 16 to determine the suitability and use of the area as a hunting ground within the greater hunting territory of the Roodekrans Verreaux’s (Black) eagles (Aquila verreaxii) currently nesting within the Walter Sisulu National Botanical Garden. Issues such as the hunting and breeding behaviour of this species as well as prey availability and human encroachment in the area were investigated.

There exists a common, although untrue, perception that this eagle is a ‘rare’ or ‘endangered’ species. Rather it is a species which is habitat specific, occurring in rocky or mountainous terrain throughout its distribution. This distribution includes semi-arid areas as well as areas with a high rainfall, but almost always coincides with the occurrence of its principal prey species, the Rock Hyrax (Procavia capensis).

The Roodekrans Verreaux’s eagles have successively occupied the cliffs adjacent to the Witpoortjie waterfall within the Walter Sisulu National Botanical Garden since the late 1940s with the current breeding pair believed to be at least third and fourth generation. Of this pair, the female is estimated to be approximately 35 years of age and the male approximately 14 years.

A Verreaux’s eagle pair will, under natural conditions, occupy a home range of approximately 14 km². Home range size is largely dependent on prey availability and the density thereof. However, in the case of the Roodekrans pair, the eagles occupy a home range of approximately 150 to 200 km², which clearly exceeds the norm. This is attributed to rapidly diminishing, and in some cases a total lack of prey availability, as a direct result of habitat loss and the rapid encroachment of human development. The dimensions of this eagle pair’s current home range are 22 km to the west (along the ridge system), 17 km to the north, 9 km to the east and 6 km to the south from the Witpoortjie nesting site respectively.  

Elsewhere in Southern Africa the breeding season for Verreaux’s eagles commences during May / June, whereas the Roodekrans pair commence breeding already in February / March. This variation is attributed to the increase in stress experienced by the pair in response to a reduced availability of prey during the mid-winter months. By commencing breeding earlier, this pair can then almost be guaranteed that prey will be relatively abundant during the critical 44-day incubation period and three-month post-hatchling stage. Verreaux’s eagles normally breed once a year and lay a clutch of two eggs. Only one chick will survive as the other is typically subjected to what is known as the ‘Cain and Abel’ syndrome.

Associated Problems

Consistent, long-term observations of the Roodekrans eagle pair undertaken by the author since 1994 have shown there to be an observeable change in the pair’s behaviour which is attributed to increased hunting stress. Aggressive behaviour has become a regular occurrence and especially intensified during the post-hatchling period of the breeding seasons of 1993 to 2003. On numerous occasions young chicks / juveniles were almost shoved off the nest during these bouts of parental aggression.

On at least four occasions in the past 13 years the pair unsuccessfully attempted to breed twice within one year, which is an abnormal activity. Of equal concern during the past 10 years is the regular occurrence of the second egg being addled. During the 1997 breeding season the female laid three eggs, each one hatching at successive three-day intervals with only one eaglet surviving. This was the first time an event of this nature had ever been recorded for this species and clearly indicates unusual behaviour.  

Observations have also shown there to be a sharp increase in the frequency with which domestic poultry, rodents, pigeons and tortoises are hunted by the Roodekrans pair. This choice of atypical prey species indicates an insufficient number of typical prey species such as the Rock Hyrax within the pair’s home range. Observations have also indicated that on numerous occasions the pair has only been able to successfully feed once over a two to three day period, despite their obvious attempts to locate prey during this time.

Poultry is considered to be highly unsuitable prey with which to rear young chicks / juveniles as these food items imprint upon the young eaglet’s memory, with the result that it will prey upon the very same species later on in life. This creates a further set of problems in that these eagles then prey upon commercial livestock and poultry, instead of their natural prey base, which often results in their untimely death.

After lengthy research and in collaboration with numerous raptor experts and scientists, a supplementary feeding programme was implemented for the Roodekrans pair in 1993. It was decided that this programme would only be effected when it became clear that the eagle pair were under extreme hunting duress. The carcasses of domestic rabbits were used due to their close resemblance to two indigenous wild species, namely the Scrub Hare (Lepus saxatilis) and Jameson’s Rock Rabbit (Pronolagus randensis), and the eagle pair took these carcasses readily.

The programme is still in operation, albeit less intensively than during the 1990s and early 2000s. Other prey species such as the Helmeted Guinea-fowl (Numida meleagris), Coqui Francolin (Peliperdix coqui), Orange River Francolin (Scleroptila levaillantoides) and Slender Mongoose (Galerella flavescens) supplement the eagles’ diet. 

However, artificial supplementation cannot be sustained indefinitely for prolonged periods of time as it may induce long-term, negative changes in the eagles’ behaviour. To counter this, a long-term programme to capture and reintroduce Rock Hyrax in suitable areas within the eagle’s greater home range was implemented in 2002. Dense, overpopulations of urban Rock Hyrax were reduced through the capture of hyrax, which were then relocated to more suitable habitat within the ridge system and further afield. Between 2002 and 2006 on a part-time basis 723 hyraxes were reintroduced at various sites, all situated within a 2 to 14 km radius of the Roodekrans eagles’ nesting site.

The aim of the project was not only to provide sufficient natural prey for the eagles, but also to recreate the self-sustainable populations of Rock Hyrax that had been known to occur in large numbers in the area 25 years previously. Sites that have current self-sustainable populations of reintroduced hyrax include Kloofendal Nature Reserve, Roodepoort, which is just 3 km southwest of Little Falls Extension 16, and Zwartkop Hill, Zwartkop A.H. However, other reintroduction sites have not been as successful. In these sites reintroduced hyrax populations have suffered extensive losses as a result of a combination of poaching, snaring by vagrants and natural predation by Caracal (Caracal caracal) and to a lesser extent by Black-backed jackal (Canis mesomelas).

Observations of the feeding habits of hyraxes at various sites within Gauteng province have shown that they tend to be mixed feeders, browsing on various trees and shrubs during summer and then reverting to grazing upon Pennisetum clandestinum (Kikuyu grass) during the winter months. They have been associated with the following tree species: Nuxia congesta, Dombeya rotundifolia, Ficus ingens, Ehretia rigida, Pappea capensis, Brachyleana rotundata and Canthium gilfillanii. Hyrax, however, tend to be viewed as a problem within the urban environment by the general public as they often destroy many a prized suburban garden overnight. 

These incidences of human-hyrax conflict were investigated in the pre- and post-reintroduction phases of the Hyrax Operation Project, as well as for the duration of the programme itself, and remain a great concern as solutions are sought to effectively manage the problem. All studies indicate that the root of the problem lies in the fact that the boundaries of suburban developments are located within too close proximity to existing hyrax populations. Planners and developers tend to demarcate the boundaries of their proposed developments in such a way so as to optimally utilize the space at their disposal, while at the same time disregarding hyrax habitat and space requirements. The ideal distance that should be allowed for between any hyrax colony and any boundary line of a development is 500 m, as these mammals are capable of walking fair distances during warm, moonlit evenings to forage.

Study Area 

Four site visits, including two ridge walks, were conducted at Little Falls Extension 16 and surrounding areas during January and February 2008. This is in addition to the numerous visits to the site by the author during the 1960s and 1990s.

The study area comprises the open space area of the Little Falls Resort accessed via Falls Road off Hendrik Potgieter Road, a developed component consisting of housing and agro-industry, and open grassveld above the rocky ridges and on the slopes. The study area is surrounded by urban development in the form of housing developments and commercial enterprises to the east and west with a network of open spaces following the ridge system in a north-south direction. Open spaces here include Poortview Ridge 3 km to the north, the Walter Sisulu National Botanical Garden a further 3 km to the north, and the Kloofendal Nature Reserve 3 km to the southwest. The site is divided into two portions by the Wilgerspruit stream flowing in a west-easterly direction through the Little Falls Resort.

The topography consists of relatively flat grassed areas to the north-east of the site, which sharply increase in gradient to form a steep, rocky ridge with a north-easterly aspect running in a northerly direction. This rocky ridge is cut by the Wilgerspruit stream, which has resulted in the Little Falls waterfall located within the Little Falls Resort. The site topography and geology appears to resemble that of the Walter Sisulu National Botanical Garden (Fig.1). Vegetation includes species such as Dombeya rotundifolia, Protea caffra, Brachylaena rotundata, Ehretia rigida, Acacia caffra, Grewia flava and Mundulea sericea as well as exotic species including the Acacia mearnsii (Black Wattle). Visits to the same site during the 1960s saw numerous hyrax colonies and Vervet Monkey (Cercopithecus aethiops) troops, which appear to be no longer present. 

Verreaux’s eagle activity

Observations on site

The Roodekrans Verreaux’s eagles were regularly observed hunting along the higher and lower slopes of Little Falls Extension 16. During two of the four site visits two successful hunts were witnessed when guinea-fowl was caught. This prey item appears to be in great abundance this season and has featured predominantly in the diet of the eagles. Both eagles were also observed hunting on the grassy slopes and rocky ridges of Little Falls Extension 1, flying in a figure-of-eight pattern in a north-south direction. 

Location of study area within the greater home range 

Little Falls Extension 16 is a frequently visited hunting site as it is only 6 km south-east of the eagles’ nesting site, as opposed to the Krugersdorp Game Reserve and Zwartkop Hill that are 20 km and 14 km distant respectively. Little Falls, inclusive of Kloofendal Nature Reserve, has always been frequented more often by the eagles as these sites are the least disturbed by development and are therefore still stocked with regular prey items such as guinea-fowl, francolin, scrub hare and rock rabbit. 

Also within the immediate vicinity of the Witpoortjie nesting site, is the Roodekrans ridge, which is at present greatly disturbed due to the construction of a six mega-litre water reservoir only 700 m northwest from the nesting site. Three kilometers northwest of the nesting site is the currently under construction residential development of Sugar Bush Estate. Along the northeastern slopes of this ridge are numerous developments in progress that also include the recently completed Silver Star Casino development. Frequent visits to each of the respective development sites during their construction phases are indicative that the eagles seldom hunt in these disturbed areas. The 600 hectare, as yet undeveloped, Kingskloof site located 7 to 11 km northwest of the nesting site is also regularly visited by the eagles. This area forms part of their extended flight path towards Sterkfontein A.H., a further 4 km northwest and ultimately towards the Krugersdorp Game Reserve, a total distance of 20 km from the nesting site. The Rhino and Lion Nature Reserve in the Kromdraai Conservancy, which is 14 km northwest of the nesting site, is frequented sporadically by the eagles. Other areas that are less frequented include Rietfontein A.H. and Honeydew A.H., situated 9 km east from the nesting site. A few reports were received of the eagles hunting free range domestic poultry in this area.   

It is clear from the above observations that the Roodekrans eagles do frequent the study area often in order to hunt and that certain of their prey species are present. It is also clear that Little Falls Extension 16 is ideally situated within the pairs’ greater home range and is in an ideal position as far as proximity is concerned (i.e. neither too far not too close) to the nesting site within the Walter Sisulu National Botanical Garden. In view of the current developmental pressure within the environs of the study area it appears that it would be of the utmost importance to retain the study area as an open area so that it may function as one of many within an open space corridor extending from Kloofendal Nature Reserve in the southeast to the Krugersdorp Game Reserve in the northwest.    

Other raptor activity

Observations on site

Other birds of prey that have been recorded within the study area and environs include: Black-shouldered Kite (Elanus caeruleus), Yellow-billed Kite (Milvus aegyptius), Black-chested Snake Eagle (Circaetus pectoralis), Little Sparrowhawk (Accipiter minillus), Steppe Buzzard (Buteo vulpinus), African Harrier-hawk (Polyboroides typus), Rock Kestrel (Falco rupicolus) and Lanner Falcon (Falco biarmicus). 

With the grassveld slopes in the region having once been ideally suited to the Secretary Bird (Sagittarius serpentarius), it is now believed to be an unlikely visitor to the now largely built environment. Although not encountered, it is highly probable that Spotted Eagle Owl (Bubo africanus) and/or Barn Owl (Tyto alba) are resident on the Little Falls Extension 16 site as streaky white markings indicative of the faeces of such birds were observed under overhanging rock face crevices. Their presence would indicate that resident rodent populations are being kept under control.  

The presence of other raptor species within the study area is evidence that further strengthens the argument that the study area is an important hunting ground and reservoir of biodiversity for top-of-the-range predators in the food chain. 

Hyrax activity

Observations on site

No evidence of resident Rock Hyrax colonies was found in the study area. In areas occupied by hyrax it is usual to find the old and fresh latrines of this species as indicated by the pungent odour of urine and the easily recognisable bleached streaking on rock faces. None of these phenomena, nor any actual animals, were sighted during this survey. Thus, the current situation is very different to the situation during the 1960s up until 25 years ago, when dense hyrax populations were often encountered by the author in the study area.  

Suitability of site for hyrax reintroduction

The open space areas on the ridge associated with Little Falls Extension 16 and Extension 1 are ideally suited to the reintroduction of Rock Hyrax as the numerous overhangs and deep nooks and rock crevices are by far the most significant encountered yet within the entire approximately 30 km ridge system. 

Key hyrax adaptations include the ability to economize on energy and resources, the ability to feed on virtually all kinds of vegetation, and a tolerance for a diversity of environmental conditions, including a wide range of altitudes, temperatures and rainfall. Hyraxes are not necessarily water-dependent and gain much of their moisture requirements from the vegetation on which they feed.

The vegetation in the study area is very similar to that encountered at previous capture and reintroduction sites and to those urban nature reserves in Gauteng where hyraxes are currently over populated. 

Hyraxes live in separate colonies that may include up to 35 mammals and are extremely territorial. A colony usually consists of 1 dominant male and a harem of several related females plus their young. Only the adolescent males are forced to leave the colony and disperse. 

As young male hyraxes are capable of covering fair distances when they are forced to disperse, it remains an essential prerequisite that a buffer zone of at least 500 m exists between residential development and that of the nearest hyrax colonies. Although this is not an absolute guarantee that hyraxes will not invade properties, caution should be exercised and adequate protective measures such as the erection of impenetrable fences be put in place in order to curtail a possible invasion.  

Human impact

Vagrant activity

Of great concern is the presence of vagrants on the slopes of Little Falls Extension 16. The degradation of fauna and flora as a result is evident due to the poaching and snaring of wildlife, indiscriminate muti collection and the use of indigenous trees such as Protea caffra for fuel-wood. Residents residing in close proximity of this area have reported that they are regularly plagued by beggars and trespassers and are affected by associated criminal activities. 

Within the Little Falls Resort, squatters were observed living in rudimentary self-built shacks within the scrub and dense undergrowth underneath large trees with free range domestic poultry and dogs roaming freely about.

Not only is the study area deemed a hostile environment for humans to wander about in, whether alone or in the company of others, but also poses an equal threat to the eagles whilst hunting as they too have to be continuously alert of their surrounds especially whilst feeding. 

As for the hyraxes, they too stand little chance of survival as both sites are unprotected from poachers. The occurrence of snares in the area is known to be rife with many having been found and later destroyed on the grassveld slopes and rocky ridges of the study area by the author.  Vagrants pose a direct threat in that hyraxes are caught and eaten to supplement their diet.

In addition, eagles may fall victim by either becoming ensnared whilst obtaining a temptingly easy “meal-in-a-snare” or by being captured and killed for muti purposes. It is plausible that such a scenario may have contributed to the overnight disappearance of the previous and perfectly healthy Roodekrans male eagle during the breeding season of March 1998. In this instance the female was forced to abort under such the duress. 

Housing developments

The abnormal breeding behaviour and inconsistent feeding habits of the Roodekrans eagles are indicative of the increased level of accumulative stress being experienced by these birds. Encroaching development within close proximity to their nesting site and within their greater home range is a major contributing factor here as the associated loss of habitat and biodiversity has led to a decline in the availability of typical prey species such as the Rock Hyrax and an overall increase in stress.   

Degradation of infrastructure

The once pristine but now derelict Little Falls Resort is largely degraded and poorly maintained, as is the Wilgerspruit stream which is noticeably lined with alien invader species and weeds. An abundance of discarded rubbish items such as rubble, bottles and cans is present in the stream and the resort grounds are overrun with exotic kikuyu grass. The verges of the Wilgerspruit stream show evidence of streambank erosion and the storm water pipes are broken, in a severe state of disrepair and leaking into the water system.

Although neither hyraxes nor the Verreaux’s eagles are necessarily water-dependent (obtaining most of their moisture requirements from their food) they will drink from a water resource if it is available. In the case of the eagles, they further make use of water for the occasional bath to cleanse their feathers. As the Wilgerspruit stream is likely to be contaminated, the consumption of water will ultimately have a negative impact upon all forms of wildlife, including the eagles and any reintroductions of hyrax into the area.  

Alien vegetation

Aggressive alien invaders like the Black wattle are rapidly gaining a foothold within the study area along the Wilgerspruit stream. Deemed useless for birds to nest in and being of little use to hyraxes to feed from (the author has never once observed a hyrax in or near such trees), the Black wattle poses a direct threat to the area’s biodiversity and severely restricts, and even prohibits, the growth of indigenous vegetation. Its only real use in the area at present is as a source of fuel-wood for the many vagrants illegally occupying the area.

Within the Little Falls Resort there are numerous copses of very tall (>20 m) alien Eucalyptus camaldulensis (Red gum) which may yet support a nesting site of a resident Black Sparrowhawk (Accipiter melanoleucus) and Ovambo Sparrowhawk (Accipiter ovampensis). The eucalypts are not alongside or within immediate vicinity of the water course and an inspection is justified prior to such tall trees being felled to determine if possible nesting sites prevail.   

Conclusion

With the continued loss of habitat within the Roodekrans Verreaux’s Eagle pair’s immediate home range, it remains imperative to their long-term survival that critical open spaces inclusive of the entire ridge system be conserved for them to hunt in with the least disturbance. Little Falls Extension 16 is one such critical site and requires the utmost protection from encroaching development. 

As development is already evident on the lower slopes immediately north of Van Staden Road and Duzi Road off Hendrik Potgieter Road, it is imperative that all new development proposals inclusive of Little Falls Extension 16 not exceed beyond the 1600 m contour level.    

As the rocky ridges are ideally suited to the reintroduction of Rock Hyrax, the presence of these mammals – that essentially used to exist here many years ago and deemed to be the principal prey items for Verreaux’s eagles – will certainly enhance eagle presence and naturally supplement their varied diet.  

However, this can only be successfully achieved if a buffer zone of a minimum of 500 m or more extending from the base of the rocky cliff faces to the proposed development boundary is imposed. The greater the distance so much the better and if this cannot be achieved it is deemed impossible to prevent wandering hyraxes from gaining access to private residential properties. Once hyraxes have become established within a built-up residential environment it is impossible to eradicate them successfully as not every hyrax will ever be caught.   

In an effort to simultaneously curb vagrant presence and enhance the occurrence of raptors and other wildlife, it is recommended that the prevailing open spaces inclusive of the entire ridge system become a conservancy that is adequately fenced and protected from undesired elements. Such a conservancy can be based upon the nearby and very successful Kloofendal Nature Reserve in Roodepoort that is managed by Jo’burg City Parks and extensively used by the public and volunteers alike for educational and environmental awareness programmes and projects. This conservancy can be funded by developers, the corporate sector and the private residential estates that would border onto the reserve. Jo’burg City Parks can manage the conservancy and the possibility of reintroducing wildlife such as antelope that used to occur in the area previously can be investigated. In this way a safe haven for the wildlife and eagles of the area can be created, which in turn will only enhance the lifestyle of the resident community and be an asset within the largely built-up urban environment of Gauteng province.  

However, should the current situation in the study area remain unchanged, it will only lead to its further degradation and an increase in illegal activity in the area. This in turn will only further endanger both the Roodekrans eagles and prevailing fauna and flora. And ultimately, yet another extremely important ridge system will have lost its true potential value and from which a recovery to its former natural state will be a mammoth, near-impossible feat to achieve. 

To ensure that the Roodekrans Verreaux’s eagles remain breeding within the relatively safe haven of the Walter Sisulu National Botanical Garden, it is of paramount importance that the willpower be shown that we, as South Africans, wish to remain the custodians of our unique African natural heritage. 

Acknowledgements      

The author wishes to acknowledge the invaluable technical assistance he received from Ms. Teresa Moore in the identification of indigenous tree species and Ms. Samantha Meyer in the compilation and editing of this report.