greater Zandvlei Estuary Nature Reserve
viability of re-introducing Karoo Scrub Robin (Cercotrichas coryphoeus)
FAIRUZ HOWA tel 021 701 7542 firstname.lastname@example.org
This docuent may not be copied or reproduced in any format without the prior written consent of the author.
PGB - Karoo Scrub Robin ringed and released at GZENR.
TABLE OF CONTENTS
1.1 Background of the research
MATERIALS AND METHOD
1.1 BACKGROUND OF THE RESEARCH PROBLEM
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 1950s. 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 1950s 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).
1.2 BACKGROUND INFORMATION ON KAROO SCRUB-ROBIN C. coryphoeus:
1.2.5 POPULATION DEMOGRAPHICS:
22.214.171.124 Breeding behaviour
126.96.36.199 Nest site
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.
a. Nest predators
d. Cooperative breeding
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
1.3 THE STUDY AREAS
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.
188.8.131.52 Distribution of Cape Flats Dune Strandveld
184.108.40.206 Landscape Features
220.127.116.11 Geology and soils
18.104.22.168. Important taxa
22.214.171.124 Threats to this vegetation type
1.4 RESEARCH OBJECTIVES:
MATERIALS AND METHOD
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:
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.
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).
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.
1. PRELIMENARY BIRD CENSUS
2. VEGETATION SURVEY
STRANDFONTEIN SEWAGE WORKS
Table 1 Average height of dominant plant species (in meters)
Table 2 Density of dominant plant species (n per hectare).
GREATER ZANDVLEI ESTUARY NATURE RESERVE
Table 3 Average heights of dominant plant species (in meters)
Table 4 Density of dominant plant species (n per hectare)
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.
3. BIRD CAPTURE
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.
4. MONITORING PROGRAM
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
Land use changes and biodiversity corridors
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.
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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