greater  Zandvlei  Estuary  Nature  Reserve

The viability of re-introducing  – Karoo Scrub Robin (Cercotrichas coryphoeus)
into the Greater Zandvlei Estuary Nature Reserve.

Compiled by:    FAIRUZ HOWA     tel 021 701 7542
Date:                 31 OCTOBER 2007
Greater Zandvlei Estuary Nature Reserve, City of Cape Town –  Nature Conservation.

This docuent may not be copied or reproduced in any format without the prior written consent of the author.

photograph by Doug Harebottle

PGB - Karoo Scrub Robin ringed and released at GZENR.



1.1 Background of the research problem
1.2 Background information on Karoo Scrub-Robin (Cercotrichas coryphoeus):
1.2.1 Classification
1.2.2 Identification
1.2.3 Voice
1.2.4 Distribution
1.2.5 Population dynamics
1.2.6 Habitat
1.2.7 Food
1.2.8 Breeding: 1. Breeding Behaviour
2. Nest site
3. Nest: a. Nest Predators
b. Eggs
c. Incubation
d. Cooperative breeding
e. Breeding success
1.3 The Study areas
1.3.1 Climate
1.3.2 Vegetation type Distribution of Cape Flats Dune Strandveld Landscape features Geology and soils Important taxa Fire Threats to this vegetation type

Research Objectives

1. Preliminary bird census
2. Comparative vegetation survey of the Greater Zandvlei Estuary
Nature Reserve and Strandfontein Sewage Works
3. Bird capture
4. Monitoring program

1. Preliminary bird census
2. Vegetation survey
3. Bird capture
4. Monitoring program










Karoo Scrub-Robins (C. coryphoeus) have not been recorded at Greater Zandvlei Estuary Nature Reserve (GZENR) over the last 50 years even though the habitat is suitable for its needs. The lack of an ecologically sensitive species such as C. coryphoeus may indicate physical obstructions that prevent the successful breeding of C. coryphoeus and their natural colonisation of suitable habitat. If this species is used as a key species, the reasons behind the local extinction of this species can be used to explain the local extinctions of other ecologically sensitive species in the Greater Zandvlei Estuary Nature Reserve. According to Bibby et al (2000), birds can be useful indicators of the state of the environment. Bibby et al (2000) add that bird species distributions can help identify areas that might benefit from site protection and conservation. The aim of the study is to determine if C. coryphoeus would successfully re-colonise GZENR after re-introduction efforts.

The bird count data of Greater Zandvlei Estuary Nature Reserve dates from 2001 to 2006. During this time period, the Zandvlei staff did not observe C. coryphoeus. Upon further investigation, the author was able to confirm that C. coryphoeus were not observed since the late 1950’s. This was reported by Trish Hayward who had spent every weekend wading the perimeter of Zandvlei and walking around its surroundings (Harebottle 2007, pers. comm). No data records were found for C. coryphoeus sightings prior to 1950, therefore it is unknown if C. coryphoeus occurred in Zandvlei prior to 1950.

Zandvlei has undergone extensive vegetation rehabilitation since the 1950’s and has become the last ecologically functional estuary on the False Bay coastline (Sheasby 2007, pers. comm). However, C. coryphoeus have not established themselves in Zandvlei Nature Reserve even though there are populations at Rondevlei Nature Reserve and Strandfontein Sewage Works which is approximately two-three kilometres to the east of Zandvlei. The vegetation types occurring at Zandvlei Nature Reserve, Strandfontein Sewage Works and Rondevlei Nature Reserve are similar, but more in depth analysis of species composition, density and canopy cover is needed to determine the extent of these similarities. In terms of infrastructure, the dual carriageway (M5) and Strandfontein Road prevent the natural movement of C. coryphoeus from colonising the surrounding areas, as this timid species prefers quieter, isolated areas that lack human development.

C. coryphoeus are also resident and sedentary so it is highly unlikely for C. coryphoeus to move from either Rondevlei Nature Reserve or Strandfontein Sewage Works to Zandvlei Nature Reserve (Oatley 2005). The young males of C. coryphoeus do not usually disperse further than three territories away from the natal territory (Lloyd 2007. pers. comm). Interspecific competition does not pose a threat to establishing a population of C. coryphoeusbecause C. coryphoeus can co-exist with many bush birds (Lloyd. 2007. pers comm).

Interspecific competition was once thought to be important by some ecologists but that is an outdated concept (Oatley 2007. pers. comm). According to Lloyd (2007. pers. comm.), C. coryphoeus is ecologically similar to the Cape Robin-chat (Cossypha caffra). However, Cossypha caffra has unequal ecological parameters and can sustain higher pressure from urban related threats (Harebottle 2007 pers. comm).

Not many predators of C. coryphoeus occur at Zandvlei. From 6 December 2006 to 1 April 2007, the author had not observed rhombic egg-eaters (Dasypeltis scabra) and boomslang (Disopholidus typus) during their respective breeding seasons. However, there is no data to support or deny that these predators occur in the reserve and at what density. However, the presence of mongooses will directly influence the breeding success of these birds (Oatley 2007. pers. comm). Nest predation is usually high so the nesting success rate is approximately 20 % (Lloyd 2007. pers comm).


The genus Cercotrichas were formerly members of the family Turdidae but now they are treated as members of the family Muscicapidae. According to Hockey et al (2005), the C. coryphoeus is classified as the following:
Kingdom: Animalia; Phylum: Chordata; Class: Aves; Order: Passeriformes
Family: Muscicapidae; Genus: Cercotrichas; Species: coryphoeus

C. coryphoeus are small bush birds that grow to 17 cm (Newman 1996). According to Hockey et al (2005), the adults of this species weigh approximately 19 g. This species has a dull grey-brown plumage that is paler on its belly (Sinclair et al 1993). The eyebrow, throat and the tips of the tail feathers are all white but the rest of the tail is black (Maclean 1996). The bill, legs and feet are all black (Hockey et al 2005; Sinclair et al 1993, 2004). According to Hockey et al (2005), the eyes of C. coryphoeus are brown. Immature individuals of this species are sooty brown with an indistinct eyebrow (Sinclair et al 1993). Hockey et al (2005) reported that juveniles of this species look similar to the adult but the mantle, rump and upper wing looks brown with fawn-coloured edges. The movement of C. coryphoeus is also a distinguishing feature. The darting movements and fanning of the tail flashing its white tips allows easy identification in the field (Sheasby 2007 pers. comm).

1.2.3 VOICE:
C. coryphoeus call is a harsh, chittering “tchik, tchik, tcheek” (Newman 1996).
Sinclair et al (1993) describe its song as a mixture of harsh grating notes and whistles. Alarm calls and contact calls are also distinct (see Hockey et al 2005).

Hockey et al (2005) describe C. coryphoeus as resident and sedentary. Maclean (1996) reported that C. coryphoeus occur in the drier parts of the South West to southern Namibia. Hockey et al (2005) add to this statement by stating that C. coryphoeus occur south of Namaqualand and Nama Karoo as well as winter rainfall areas. There are few records of C. coryphoeus occurring east of 28”E. C. coryphoeus is endemic to their distribution areas therefore this species can only occur in their distribution areas and nowhere else in the world making the protection of this bird species vital for maximum biodiversity (Sinclair et al 1993).

Hockey et al (2005) estimates that 2 pairs occupy a hectare in the southern Karoo drainage woodland. In the west coast strandveld, territories are estimated to be at 0.5 hectares (Hockey et al 2005). C. coryphoeus are a long-lived bush bird species and can live to 5 years 7 months (Hockey et al 2005).

1.2.6 HABITAT:
Sinclair et al (1993) reported that Karoo scrub and fynbos provide a good habitat for C. coryphoeus to live in. Maclean (1996) adds that thickets and riverine bush in semi-deserts also provide good habitat. According to Hockey et al (2005), C. coryphoeus prefer bare ground underneath 1 m high vegetation. Lloyd (2007 pers. comm) reported that the cover of fruiting plants such as Chrysanthemoides, Nylandtia, Lycium, Rhus and Cissampelos are important plants for the ideal habitat. Hockey et al (2005) add that C. coryphoeus will occasionally forage in the intertidal zones of sandy beaches and collect nest material.

1.2.7 FOOD:
According to Hockey et al (2005), C. coryphoeus feed primarily on insects that are on the ground. Hockey et al (2005) also reported that C. coryphoeus eat the following food items:

  •  Worker ants belonging to the genus Anoplolepis custodiens (Pugnacious ant), Camponotus (Spotted sugar ant and Bal-byter), Crematogaster peringueyi (Cocktail ant), Dorylus helvolus (Red driver ant), Meranoplus, Messor capensis (Harvester ant), Monomorium, Ocymyrmex, Pheidole, Technomyrmex or Tetramorium capense.

  • Termites – mostly Microhodotermes viata (Southern Harvester termite)

  • Beetles belonging to the genus Carabidae, Chrysomelidae, Curculionidae, Elateridae, Leiodidae, Scarabaeidae and Tenebrionidae.

  • Caterpillars

  • Moths

  • Grasshoppers

  • Spiders

  • Flies and fly larvae

  • Wasps and bees

  • Small fruits from Rhus species and Lycium species are also plucked from bushes.

1.2.8 BREEDING: Breeding behaviour
According to Hockey et al (2005), C coryphoeus are monogamous and have strong bonds with their respective mate. Nalwanga et al (2004) adds that breeding pairs remain in their defended territory every year. The breeding season of C. coryphoeus is from July to November (Lloyd 2007 pers. comm). Nest site
Nalwanga et al (2004) observed the following nest-site characteristics of C. coryphoeus:

  • C. coryphoeus nest low at mean nest height between 0.18 – 0.51 m

  • C. coryphoeus would usually nest in relatively short plants with mean nest-plant heights between 0.64 – 0.91 m.

  • C. corphoeus were observed nesting in the lower half of nest plants.

  • C. coryphoeus were also observed nesting near the lateral edge of plant foliage at mean distances between 0.22 – 0.37 m.

According to Nalwanga et al (2004), C. coryphoeus typically nest in open spaces and on occasion, on the ground under tree stumps. Hockey et al (2005) stated that 95 % of the nests are placed on the ground at the base of small shrubs or in an artefact like an old tin. Nest
According to Hockey et al (2005), the nest is usually an open, deep cup sunk into a platform of large twigs. Some of these twigs are too heavy to be carried in flight and are usually dragged instead. The cup lining may include fine grass, moss, and dry flower heads, hair from sheep and goats as well as tufts of fur from hares and smaller rodents that is extracted from the scats of small carnivores such as mongoose (Hockey et al 2005). The female builds the nest with the male watching from a nearby lookout post but some males are known to help gather the nest material (Oatley 2003). According to Hockey et al (2005), construction of the nest usually takes 5-6 days until the outside diameter and cup diameter is on average 114 mm and 60 mm respectively. The ramp is usually 220 mm long and 170 mm wide (Hockey et al 2005).

a. Nest predators
According to Lloyd (2007 pers. comm), the main nest predators of C. coryphoeus are the Rhombic Egg-Eater (Dasypeltis scabra), Boomslang (Disopholidus typus), crows (Corvus spp) and mongoose species, Galerella pulverulenta and Atilax paludinosus. Lloyd (2007 pers. comm) adds that the egg-eater feeds on the eggs of C. coryphoeus while boomslang feed on chicks. However, Oatley (2003) observed that some early nests were robbed during periods when ambient temperatures were too low for reptilian mobility. When a nest is robbed, the owners will build another relatively soon unless it is late in the season (Oatley 2003). C. coryphoeus will mob nest predators and the territorial male will frequently follow the progress of mongoose through the vegetation while uttering the alarm call (Oatley 2003). Oatley (2003) adds that small grey mongoose, G. pulverulenta, are not entirely diurnal animals so they may be responsible for robbing nests at night. Nalwanga et al (2004) identify two ways in which nest predation is minimised:
(1) Select safer nest sites and
(2) by randomly dispersing nests in space and time to reduce potential density-dependent predation.

b. Eggs
In the Western Cape, C. coryphoeus will lay eggs from July to November (Lloyd 2007). The clutch size is normally three eggs (Oatley 2003) that weigh approximately 2.3 g (Hockey et al 2005). These eggs are aquamarine to turquoise with bold, spotted blotches that are dark brown, purple and grey in colour and usually occur over the obtuse half of the egg where markings combine to form a cap or ring (Hockey et al 2005). According to Hockey et al (2005), these eggs are oval or elliptically oval. These authors add that C. coryphoeus will relay up to four times after breeding failure, which may help the success of the re-introduction at Zandvlei Nature Reserve.

c. Incubation
The incubation period will usually start once the clutch is completed. The period of incubation is 13-15 days and only the female incubates these eggs (Hockey et al 2005). Hockey et al (2005) add that the male frequently feeds the female during the incubation period.

d. Cooperative breeding
According to Perrins (1983), cooperative breeding has been recorded in over 150 species in ten diverse orders of birds. Cooperative breeding systems have the following characteristics (Perrins. 1983):

  • Low breeding rates

  • High adult survival

  • Low dispersal

  • Occupy stable environments

  • Sexual dimorphism is rare

  • All purpose territories that group members defend

Oatley (2003) observed cases where more than two adults would feed chicks and that the adults would even queue up in order to feed the chicks. Some of these adults that aided the breeding pair were nestlings that were fledged from the first nest of the season and only 10 weeks old at that time (Oatley 2003). According to Oatley (2003), these helpers not only feed the chicks but will also pass food to the breeding male who would in return feed the nest-building female. Adults that had helpers were known to have a higher breeding success rate and that cooperative groups have more eyes to spot approaching predators as well as extra voices to sound the alarm in case of predators (Oatley 2003). The fact that adults wait their turn to feed nestlings does not the support food-limitation hypothesis as a reason for low breeding success (Oatley 2003).

e. Breeding success
As previously stated, the breeding success is often low at 20 % (Lloyd 2007 pers. comm).

1.3.1 Climate
The Greater Zandvlei Estuary Nature reserve and Strandfontein Sewage Works are both situated in a Mediterranean climate that experiences cool, wet winters and hot, dry summers (Nalwanga et al 2004). The summer months are from October to April and the winter months are from May to September (South African Weather Service 2003). The South African Weather Service (2003) has recorded an average minimum and maximum temperature for summer 16°C and 26°C respectively. The average minimum and maximum temperature for winter is 8°C and 18°C respectively (South African Weather Service 2003).

The climate of the Cape Peninsula is predominantly controlled by two systems. During summer months, the Atlantic high-pressure systems (with an anti-cyclone wind flow) are located in the south (Paterson-Jones 1991). Mucina & Rutherford (2006) reported that these high-pressure systems are located near 37° S in summer. According to Paterson-Jones (1991), this pressure system forces cold fronts away from the continent and causes strong south easterly winds to blow after relatively calm conditions. As winter approaches these pressure systems move north to approximately 32° S (Mucina & Rutherford. 2006) and allow cold fronts to cross the Western Cape and penetrate inland for varying distances (Paterson-Jones 1991). According to Paterson-Jones (1991), these cold fronts cause strong, north-westerly winds to blow and rain will follow after a couple of days.

During dry summers, cloud cover is frequent and fuelled by strong winds (Mucina & Rutherford. 2006). Mucina & Rutherford (2006) report that over 500 mm of water can be precipitated per year without being recorded on standard rain gauges.

Mucina & Rutherford (2006) also report that relative humidity is highest along the coast in summer but high values are also reached inland during winter. In terms of wind speed, the southerly gradient winds are reinforced by the sea breeze over False Bay and raises maximum wind velocities in the early afternoon (Mucina & Rutherford. 2006). Rutherford & Westfall (1994) add that lightning frequency and hail are rare in the western parts of the biome, where the two study sites are located.

1.3.2 Vegetation Type

The study sites are located within the Fynbos biome, a biome renowned for its floristic diversity. The fynbos biome is characterised by the co dominance of evergreen, sclerophyllous plants that do not exceed three metres in height (Rutherford & Westfall. 1994). Within the fynbos biome, many different vegetation types exist depending on the geology, soil and other environmental conditions occurring at a particular area.

The vegetation type of both GZENR and Strandfontein Sewage Works is classified as strandveld. Cowling et al (2003) describe strandveld as a dense to open shrubland of medium height (0.5 – 1.5 m) and a biomass of 3500 – 8250 g m-2. Cowling et al (2003) add that the vegetation in this vegetation type is mostly sclerophyllis, deciduous and evergreen plants that are mostly shrubs, grasses and restios in terms of growth forms. Mucina & Rutherford (2006) add that the shrub structure of this vegetation type is extremely low especially when it is closer to the seashore due to stunting from salt spray, high winds and extreme conditions. Both GZENR and Strandfontein Sewage Works are further classified as Cape Flats Dune Strandveld. Distribution of Cape Flats Dune Strandveld
The largest section of this veld type extends across the south coast of False Bay, between Muizenberg and Gordon’s Bay (Mucina & Rutherford. 2006). Landscape Features
According to Mucina & Rutherford (2006), this vegetation type has a flat or slightly undulating landscape between 0 – 80 m above sea level. However, the altitude may reach up to 200 m in places (Cowling et al. 2003). Geology and soils
According to Munica & Rutherford (2006), this vegetation type is formed on mostly tertiary to recent calcareous sand that originated from marine sediments and overlying metasediments of the Tygerberg formation. According to Cowling et al (2003), outcrops of Sandveld Group limestone are also found along the False Bay coast. Important taxa
Most authors (Acocks. 1988; Cowling et al. 2003; Mucina & Rutherford. 2006) refer to the following taxa as being important to this vegetation type:
Chrysanthemoides monilifera; Euclea racemosa subsp. Racemosa; Helichrysum species; Lessertia fruticosa; Lycium; Metalasia muricata; Morella cordifolia; Nylandtia spinosa; Otholobium bracteolatum; Passerina species; Pelargonium; Phylica species; Rhus species; Salvia africana-lutea. Fire
Fire plays a lesser role in strandveld communities. The fire frequency is usually low. Mucina & Rutherford (2006) report there is no data on fire-return intervals for strandveld currently exist but the interval is probably between 50 – 200 years. Threats to this vegetation type
According to Low & Rebelo (1996), this vegetation type is under threat from urbanization. These areas are often encroached by human developments and infrastructure. Alien vegetation is another threat to this vegetation type. Acacia cyclops and Acacia saligna are common invaders in this vegetation type and often decrease the biodiversity of this vegetation type.

1. Determine a site in Strandfontein Sewage Works where C. coryphoeus can be captured and translocated by doing a bird count census in the source area. 
2. Determine whether the flora of the Greater Zandvlei Estuary Nature Reserve can support C. coryphoeus by doing a comparative vegetation survey with Strandfontein Sewage Works.
3. Select the source site within Strandfontein Sewage Works based on vegetation comparison and the number of birds in the source site.
4. Trap and translocate a small population of approximately three pairs of C. coryphoeus to start up a breeding population at the Greater Zandvlei Estuary Nature Reserve. Birds need to be ringed with colour combinations for easy identification in the field.
5. Implement a monitoring programme to record the progress of the population.


1. Preliminary bird census: A preliminary bird census was undertaken to determine areas where the breeding pairs occur at Strandfontein Sewage Works. This census was used to establish the birds’ breeding territories and to give an approximation of the population size.

This census was done by:
1. Using spishing, a vocalisation that stimulates curious behaviour in bush birds. According to Sheasby (2007 pers. comm), spishing does not affect the breeding success of birds if used sparingly and out of the breeding season.
2. Flushing by walking through the vegetation to flush out the birds (Sheasby 2007 pers. comm).

The latter was used more frequently because the census was undertaken during breeding season. Visits were limited to periods when this species were most active, which was early morning (Bibby et al. 2000). To avoid bias, the census time was standardised and the route was walked at a slow pace so that all birds could be detected and identified.
Once a C. coryphoeus was observed in the area, it was recorded on a sightings list and the coordinates of the area were recorded using Global Positioning Satellites.

2. Comparative vegetation survey of the Greater Zandvlei Nature Reserve and Strandfontein Sewage Works: Materials needed:  5 steel droppers that are 1.5 m in height and 10 mm in diameter, string marked out at 1 m intervals.

Method: The two study sites were selected according to vegetative comparison and number of birds. Within each study site, five stratified random plots were sited in plant stands that appeared to be floristically and structurally homogenous (Werger 1974).
Sample plot size was 10 m x 10 m, which result in 5 plots of 100 m2 each. These plots were marked out using four steel droppers and the marked string. Another string was placed from one corner of the plot to the other. The density and height of the 5 most dominant plant species was recorded in each plot.

Two transects were sited in the study area measuring a total of 200 m. A steel dropper was used to record the growth form at each canopy strike (Campbell et al 1981) that was recorded at 1 m intervals along transects. The following was also recorded at 1 m intervals: rock, soil, litter and basal strikes.

The terminology used by Campbell et al. (1981) will be used for the vegetation description.

3. Bird Capture: A combination of spring traps and mist nets was used to capture C. coryphoeus. The recommended method was to use spring-traps that were baited with a live Yellow Mealworm, Tenebria molitor (Lloyd 2007 pers. comm). According to Bibby et al (2000), mist nets are functional to capture shy species that are usually missed in the average survey but setting up and manning the mist nets is very time consuming. The specimens were ringed with a SAFRING metal ring on the right leg. On the left leg, the specimens were individually colour banded using a combination of pink, blue and green. The specimens were named after the sequence of those three colours.

Blood samples were taken from specimens using a capillary tube and stored in vials with a Lysis buffer (Lloyd 2007 pers. comm). The birds were placed into bird-ringing bags and hung up for transport to the Greater Zandvlei Estuary Nature Reserve for the release of specimens.

4. Monitoring Programme: A sightings list was kept to monitor the progress of population as foreign females may enter from elsewhere (Lloyd 2007 pers. comm). The following was recorded: Date; Type of sighting; Number of birds; Type of sighting; GPS coordinates

As part of a monitoring program, a recapture operation was attempted using spring traps baited with mealworms.




09-Jul-07 Confirmed - visual   2 Strandfontein  –
  Confirmed - visual 2 Strandfontein –
  Bird Call 2 Strandfontein –
17-Aug-07 Confirmed - visual 2 Strandfontein –


Tables 1 and 2 respectively indicate the average heights and densities of the dominant plant species from the study site in Strandfontein Sewage Works.

Table 1 Average height of dominant plant species (in meters)



  1 2 3 4 5 Average
1. Metalasia muricata  1.01 1.4 0.86 – – 1.09
2. Salvia africana lutea 0.71 0.81 0.93 0.67  0.77 0.78
3. Rhus lucida  0.78 0.83 0.53 – 0.47 0.65
4. Otholobium bracteatum 0.53 – 0.35  – – 0.44
5. Phylica ericoides 0.15 0.19 0.25 0.11  0.19 0.18
6. Passerina vulgaris  – – – 0.19  0.16  0.18
7. Nylandtia spinosa – – – 0.14 –  0.14

Table 2 –  Density of dominant plant species (n per hectare).

  1  2 3 4  5 N/HA
1. Metalasia muricata 4 1 7 – –  240
2. Salvia africana lutea 10 26 29 21 20 2120
3. Rhus lucida 11 3 – 520
4. Otholobium bracteatum 2 – 10 – – 240
5. Phylica ericoides 17 12 12  35 13 1780
6. Passerina vulgaris – – – 7 520
7. Nylandtia spinosa  – – – 5 – 100

Tables 3 and 4 – respectively indicate the average heights and densities of the dominant plant species from the study site in the Greater Zandvlei Estuary Nature Reserve (GZENR)

Table 3 Average heights of dominant plant species (in meters)

  1 2 4 5 Average
1. Metalasia muricata  1.05 0.83 0.96 – 0.93  0.94
2. Passerina vulgaris  0.89 0.3 0.64  0.25 0.3 0.48
3. Nylandtia spinosa   – 0.25 0.22 0.27 0.23 0.24
4. Senecio burchellii  0.36 0.32 – 0.26 – 0.31
5. Ehrharta villosa  0.74 0.6  0.54 0.75 0.66 0.66
6. Juncus krausii  0.41 – – – –  0.41
7. Leucodendron coniferum 1.7 – – – – 1.7
8. Morella cordifolia  – – – 0.35 0.5 0.42

Table 4 Density of dominant plant species (n per hectare)



  1 2 3 4 5 N/HA
1. Metalasia muricata 37 9 10 – 8 1280
2. Passerina vulgaris 24 19 23  31 40 2740
3. Nylandtia spinosa – 19 19 6 11 1100
4. Senecio burchellii 16 8 – 9 – 660
5. Ehrharta villosa 176 268  216  264  132  21120
6. Juncus krausii  19 – – – – 300
7. Leucodendron coniferum – – – – 40
8. Morella cordifolia – – – 27  33  1200

Figure 1 and 2 respectively compares the growth form cover, basal cover and substrate cover of Strandfontein Sewage Works and GZENR.

Figure 1 This bar graph compares the percentage of growth forms in GZENR and Strandfontein Sewage Works to indicate similarities and differences in the two habitats.

Figure 2 This bar graph indicates the similarities and differences between the basal and substrate cover of the two habitats located at Strandfontein Sewage Works and the Greater Zandvlei Estuary Nature Reserve.



I. The source site at Strandfontein Sewage Works

Three strata were recorded in this low mid-dense shrubland.

The mid high sparse shrub stratum (1 – 2 m) has a canopy cover of 7% and is dominated by Metalasia muricata (240/ha; 1.09 m). No other dominant species were noted in this stratum.

The low mid-dense shrub stratum (0.25 – 1 m) has a canopy cover of 71% of which graminoid and shrub components were 11% and 60% respectively. The shrub component was dominated by the following species: Salvia africana lutea (2120/ha; 0.78 m), Rhus lucida (520/ha; 0.65 m) and Otholobium bracteatum (240/ha; 0.44 m).

The dwarf sparse shrub stratum (less than 0.25 m) has a canopy cover of 22% of which the geophyte and shrub components were valued at 1% and 21% respectively. This stratum is dominated by Phylica ericoides (1780/ha; 0.18 m), Passerina vulgaris (520/ha; 0.18 m) and Nylandtia spinosa (100/ha; 0.14).

The percentage cover for basal cover, litter, rock and bare ground is 0%, 47%, 0% and 53%.

II. The release site at the Greater Zandvlei Estuary Nature Reserve

Three strata were recorded in this low mid-dense shrubland.

The mid-high sparse shrub stratum (1 – 2 m) has a canopy cover of 23% and is dominated by Leucodendron coniferum (40/ha; 1.7 m). No other dominant species were noted in this stratum.

The low mid-dense graminoid shrub stratum (0.25 – 1 m) has a canopy cover of 55% that contained graminoid and shrub components of 4% and 51% respectively. The shrub component was dominated by Passerina vulgaris (2740/ha; 0.48 m), Senecio burchellii (660/ha; 0.31 m). The graminoid component is dominated by Ehrharta villosa (21120/ha; 0.66 m).

The dwarf sparse shrub stratum (less than 0.25 m) has a canopy cover of 22%. It is dominated by Nylandtia spinosa (1100/ha; 0.24 m). No other dominant species were noted in this stratum.
The percentage cover of basal cover, litter, rock and bare ground is 3%, 35%, 0% and 62% respectively.


On the 13th July 2007, one specimen of C. coryphoeus was captured at Strandfontein Sewage Works using a mist net. The specimen was processed and transported as described in the Materials and Method section.

Another trapping session was attempted using spring traps in the same area to capture the mate of this specimen. However, no specimens of C. coryphoeus were caught.








14-Jul-07 Unconfirmed visual 1 GZENR 


17-Jul-07 Unconfirmed visual 1 GZENR  –
14-Aug-07 Bird Call 1 GZENR  –
15-Aug-07  Unconfirmed visual 1 GZENR  –
22-Aug-07 Unconfirmed visual 1 GZENR  –
30-Aug-07 Unconfirmed visual 1 GZENR  –
3-Sep-07 Unconfirmed visual 1 GZENR  –
27-Sep-07  Unconfirmed visual 1 GZENR  –
11-Oct-07 Bird Call 1 GZENR  –
16-Oct-07 Bird Call 1 GZENR  –

On the 16th October 2007, a recapture attempt of C. coryphoeus was attempted at GZENR to determine if any new C. coryphoeus individuals had moved into the area naturally. However, no specimens were caught but a bird call was heard between 07:30 – 08:00.


In terms of vegetation structure and species, this study indicated many similarities between the vegetation of the Greater Zandvlei Estuary Nature Reserve and Strandfontein Sewage Works.

Both Strandfontein and GZENR are classified as low mid-dense shrublands. The vegetation descriptions of both these areas indicate that there are three distinct strata to the vegetation structure and that the vegetation height will not exceed two meters. In both the study areas, one species dominated the highest strata (1 – 2 m) and no other species were observed at this strata level. The lower strata levels in both study sites contained graminoid and shrub components in similar ratios.

In terms of flora species, nearly all the species that occurred in the study site at Strandfontein occur in GZENR except some species are not as dominant as they are in Strandfontein. However, in tables 1 and 2, there are three species in common that were dominant in both study sites: Metalasia muricata, Passerina vulgaris and Nylandtia spinosa.

Figure 1 indicates that the differences in percentage cover of the different growth forms in both GZENR and Strandfontein are not. The only significant difference that occurs in the graph is the percentage cover of mid-high shrubs. The mid-high shrubs that occur in GZENR are at 23% whereas the mid-high shrubs that occur in Strandfontein are at 7%.

From figure 2, the graph indicates the differences in basal and substrate cover. GZENR is not significantly different from Strandfontein in terms of substrate cover. GZENR has 9% more bare ground than Strandfontein whereas Strandfontein has 12% more litter on the ground than GZENR. Both study sights had 0% rock. Only GZENR had basal strikes but the amount of these strikes was not significant enough to indicate an actual difference in the habitats.

The monitoring program was undertaken after the capture of C.coryphoeus specimen, PGB. On most occasions, the colour tags of PGB were not seen and any sighting of C. coryphoeus without tags was considered new specimens that had moved in from elsewhere. These specimens were recorded as “Unconfirmed visuals” on the sightings list. After the introduction of PGB, one untagged specimen was constantly sighted in the release area. The recapture operation was attempted to trap this individual and PGB to confirm its presence at GZENR but the attempt failed and no specimens were caught in a 4-hour period with the traps being checked every 15-30 minutes. However, two of the traps had to be re-baited thus indicating that an insectivorous bird species was occupying the release area. The visual sightings and the C.coryphoeus bird calls observed in the release area strongly suggest that C. coryphoeus is still occupying the area.


The primary objective of this study was to determine the viability of re-introducing the Karoo Scrub-Robin (Cercotrichas coryphoeus) into the Greater Zandvlei Estuary Nature Reserve. The data produced from this study indicates that re-introducing C. coryphoeus into the GZENR is a viable option to increase the biodiversity value of GZENR and aiding the continuation of this ecologically sensitive species. In terms of floristic structure and species, the release site at GZENR will be able to support the ecological needs of C. coryphoeus. In terms of substrate cover, the site at GZENR will support the movement needs of C. coryphoeus since it moves around by running and hopping on open ground. From the monitoring program, it can be determined that C. coryphoeus individuals will survive the environmental conditions at GZENR. C.coryphoeus at GZENR are likely to bring other C. coryphoeus from other areas and diversify the gene pool of the pioneer population at GZENR. This study needs further data and appropriate management to monitor the population of C. coryphoeus and determine the nature of its population dynamics in order to maintain the genetic diversity of the population.


Veld manipulation for maximum biodiversity
It strongly recommended that the release site at GZENR be cleared of waxberries, Morella cordifolia. The previous manager of GZENR introduced this plant species into the site. This plant species is indigenous but it has become invasive in the area. This species has impacted the floristic diversity in the area and areas cleared of this species have shown flowering plants that were not seen previously in the area. M. cordifolia is already a dominant species in this site (refer to Table 3 and 4). Large stands of this species could cause excessive canopy cover and could change the low mid-dense shrubland into a closed shrubland. It would also cause a drastic increase in basal cover and limit the amount of bare ground. This is detrimental to the needs of C. coryphoeus as it needs bare ground to move around when it is not flying or roosting.

Land use changes and biodiversity corridors
C. coryphoeus is ecologically sensitive to urban developments due to the timid nature of the bird. It is recommended that conservationists are consulted with for any changes in land use around nature reserves as developments such as housing and road infrastructure might affect the distribution of this species by genetically isolating them from other C. coryphoeus populations. The development of biodiversity corridors is vital to prevent this situation. Certain sections of Strandfontein Road should undergo extensive rehabilitation by removing the alien vegetation and introducing coastal shrubs. Recreational areas towards the estuary mouth of GZENR should also add natural vegetation to contribute to the natural movement of C. coryphoeus amongst coastal scrub.

Bird capture
It is recommended that five more specimens of C.coryphoeus be moved to GZENR so that the pioneer population contains at least six individuals to colonise the area. It is also recommended that mist nets be used in conjunction with spring traps as this will increase the chance of capturing more than one C. coryphoeus at one trapping session. However, this will only be a viable option if there is enough manpower to man the mist nets. Volunteers aiding in the capture of C. coryphoeus should be briefed beforehand on the nature of the bird and the research. Supervisors of the trapping session should make sure that the volunteers do not disturb the birds excessively.

It is recommended that if both members of a pair could not be caught in one trapping session, the individual should be released after being processed. C. coryphoeus are monogamous birds and the stress of being away from its mate may encourage the bird to move out of the release area. This may even affect the reproductive success of the pair as there will be less parental care for chicks if the pair is caught in breeding season. However, it is strongly recommended that the birds should be caught prior to breeding season; therefore trapping should take place from November to June. If the individual from a pair is caught and processed, it would be easier for the researcher to determine the sex and any hormonal changes in the individual from the blood tests.

It is recommended that the entire pioneer population are rung with SAFRING serial numbers and that chicks should be rung if they are found in nests. Regular ringing sessions should also be undertaken so that sufficient data can be gathered on sex ratios and genetic lineage can be determined if other C. coryphoeus move into the area.

It is also recommended that the pioneer population be fitted with tracking chips to monitor movement effectively. This will allow researchers to map breeding territories efficiently and allow the observers to find and monitor nests. This recommendation can only be implemented if there are sufficient funds to buy and maintain this equipment. Staff will also need to be trained to use the equipment properly, which will cost money and time.

Public participation
Public should be encouraged to participate in the project by reporting any sightings of colour tags, individuals or chicks in the nature reserve. This can be added to the sightings list and aid in the monitoring of the population.

I would like to thank the following people for their time, resources and information that proved to be invaluable to this project:

Doug Harebottle; Marius Wheeler; Penn Lloyd; Terry Oatley, Dalton Gibbs; Cassandra Sheasby; Tim Szoke; Mark Arendse, Edward Moses; Glendon Potgieter; Gavin Lawson, Silke Stephan; Laurence Walbrugh; Trish Hayward.


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