BIRD IMPACT ASSESMENT STUDY BIRD HELICOPTER INTERACTION THE BITOU RIVER

Transcription

1 BIRD IMPACT ASSESMENT STUDY BIRD HELICOPTER INTERACTION THE BITOU RIVER Phase 1 Predictive Scoping Study Albert Froneman Endangered Wildlife Trust Tel: +27 (0) Private Bag X11 Fax: +27 (0) Parkview albertf@ewt.org.za 2122 September 2006 Phase 1 Predictive Scoping Study

2 EXECUTIVE SUMMARY As a result of the periodic use of private helicopter along the Bitou river during April and December/January, and the fact that certain bird species are known to be impacted through interaction with aircraft / helicopters, the following main issues were identified for consideration during the specialist bird aircraft interaction study: Occurrence of Red Data bird species in the study area Effect of helicopter disturbance on bird communities Potential for bird collisions during low level scenic flights Mitigating measures The lower reaches of the Bitou and Keurbooms River forms a unique estuarine system supporting a wide variety of habitat types and a rich diversity of bird species. Aircraft movements are known to impact on various bird species, through causing disturbance to the birds. The birds themselves can also affect the safe operation of aircraft especially during low level movements when the risk of collisions with birds i.e. bird strikes is greatly increased. The study concluded that low flying aircraft and or helicopter movements are likely to have a negative effect on bird behaviour, albeit for a sort period during the actual activity only. Little research has however been done to evaluate the long terms effects of low flying aircraft on bird populations. The temporal nature of the propose helicopter movements (i.e. April and December) would also negatively affect potential habituation over a longer period of time. A real risk also exists in terms of experiencing a bird strike during low flying operations, especially so taking into consideration the potential aggressive behaviour from birds of prey i.e. the Africa Fish Eagles known to have bred in close proximity to the helicopter hangar. An analysis of Coordinated Waterbird Counts (CWAC) data collected since 1995 indicated that there is no seasonal preference by birds for the wetlands of either the Bitou or Keurbooms rivers. It can therefore be deduced from the CWAC data that the presence and diversity of birds on the wetlands are largely determined by water levels and associated available habitat. There is however no clear trend that emerges from the CWAC waterbird counts and it would therefore not be reliable to use this data in order to evaluate or predict the effects of one the helicopter movements over the study area or two any other anthropogenic or natural disturbances. A pair of Blue Cranes and a pair of Africa Fish Eagles are known to have nested on the polo estate and particular care should be taken not to disturb these birds. Although the Keurbooms / Bitou River systems and estuary does not support in excess of waterbirds the fact that the Keurbooms estuary is of high conservation significance and that it supports at least 1% of the population of a waterbird species/s (Kelp Gulls) there is a good case for elevating its conservation and Ramsar status. The study concluded with a recommendation that a minimum flying altitude of at least 450m (AGL) (ca ft) be instigated over the Keurbooms and Bitou Rivers of in order to minimise the effect that low level aircraft movements could have on waterbirds. The presence and interest to again nest there of the pair of Africa Fish Eagles on the polo field property should be further investigated. If the birds are found to gain be interested in using the existing nest helicopter flights shoud be restricted to the non-breeding summer months. Further monitoring of the actual impacts are also proposed, both in terms of the helicopter movement at different heights and the situation with regard to the pair of African Fish Eagles. Taking into account conservation value and sensitivity of the habitat in the study area the changes brought about in the past and the continued increase in human related activities in the area effort should be made to conserve the Keurbooms / Bitou River systems and estuary. Phase 1 Predictive Scoping Study Page 2 of 29

3 BIRD IMPACT ASSESMENT STUDY BIRD HELICOPTER INTERACTION THE BITOU RIVER Phase 1 Predictive Scoping Study CONTENTS Chapter Description Page 1 INTRODUCTION Background Study Approach Methodology Sources of information Limitations & assumptions 5 2 DESCRIPTION OF AFFECTED ENVIRONMENT Topography & vegetation Bird micro habitats Relevant bird populations 9 3 PRELIMONARY PREDICTION OF INTERACTIONS AND IDENTIFICATION OF RISK SOURCES Description of bird aircraft interactions Potential disturbance caused by the helicopter movements Risk of bird strikes during low level helicopter flights Existing helicopter operations along the Bitou River and Keurbooms River BIRD POPULATION ASSESSMENT CWAC Counts Specific species of concern Blue Crane (Anthropoides paradiseus) African Fish Eagle (Haliaeetus vocifer) Evaluation in terms of Ramsar criteria Cumulative impact assessment 21 5 RECOMMENDED MITIGATION MEASURES 23 6 CONCLUSION 25 7 REFERENCES 26 Phase 1 Predictive Scoping Study Page 3 of 29

4 1 INTRODUCTION 1.1 Background As a result of the periodic use of private helicopter transport along the Bitou river during the polo season (April and December/January), and the fact that certain bird species are known to be impacted through interaction with aircraft / helicopters, the following main issues were identified for consideration during the specialist bird aircraft interaction study: Occurrence of Red Data bird species in the study area Effect of helicopter disturbance on bird communities Potential for bird collisions during low level scenic flights Mitigating measures The study area will encompass the greater Bitou estuary and lower river system and will attempt to assess, evaluate and rank impacts on wetland birds so as to meaningfully compare significance of different impacts within the Bitou catchment. Due to the paucity of information relating to bird helicopter interactions around wetlands, it was considered prudent to break the bird helicopter interaction study into two phases namely: Phase 1 Predictive Scoping Study Phase 2 Impact Measurement Environmental Science Associates were appointed as main consultants to assess the Environmental Impacts of the Polo Field and associated developments on the Stonefield Property, and subsequently appointed the Endangered Wildlife Trust (EWT) to conduct the specialist Avifaunal Impact Assessment Study with reference to the helicopter movements. Aircraft movements are known to impact on various bird species, through causing disturbance to the birds. The birds themselves can also affect the safe operation of aircraft especially during low level movements when the risk of collisions with birds i.e. bird strikes is greatly increased. This phase 1 Predictive Scoping Study will involve a desktop exercise to predict the potential impact of the helicopter movement on the birds. The impact that the birds (especially the Fish Eagles) can have on the safe operation of the helicopter will also be evaluated. Based on the outcome of the desktop study a monitoring and evaluation project will be recommended. 1.2 Study Approach Methodology In predicting impacts of the helicopter movements along the Bitou, a combination of science, field experience and common sense is required. More specifically the methodology used to predict impacts in the current study was as follows: The various data sets discussed below under sources of information were collected. Phase 1 Predictive Scoping Study Page 4 of 29

5 This data was examined to determine the presence and abundance of Red Data species as well as non-red Data water bird species potentially sensitive to the disturbance in the in the study area. The area was visited to obtain a first-hand perspective of the site and birdlife and to determine which bird micro-habitats are present and relevant to the study. The impacts of the helicopter on the birds and vice versa were predicted on the basis of experience in gathering and analysing data on bird and wildlife hazard management at South African airports since 1999 and experienced gained through the International Bird Strike Committee Sources of information The study made use of the following data sources: Bird distribution data of the Southern African Bird Atlas Project (SABAP Harrison, Allan, Underhill, Herremans, Tree, Parker & Brown, 1997) obtained from the Avian Demography Unit of the University of Cape Town, in order to ascertain which species occur in the study area. Data collected by members of BirdLife Plettenberg Bay since 1995 from the Co-ordinated Waterbird Count (CWAC) project was also used to determine which species occur on both the Bitou and Keurbooms River systems. (Taylor, Navarro, Wren-Sargent, Harrison & Kieswetter, 1999). The conservation status of all bird species occurring on the Bitou and Keurbooms River estuary and wetlands was then determined with the use of The Eskom Red Data book of birds of South Africa, Lesotho and Swaziland (Barnes, 2000). The bird strike incident database of the Airports Company South Africa /Endangered Wildlife Trust Strategic Partnership (1999 to present) and ICAO data on bird weights which pose a risk to aircraft was consulted to determine which of the species occurring in the study area are most likely to pose a risk to the safe operation of the helicopter. A classification of the vegetation types in each degree square was obtained from Harrison, Allan, Underhill, Herremans, Tree, Parker & Brown (1997). Information on the micro-habitat level was obtained through visiting the area and obtaining a first hand perspective. Electronic 1: maps obtained from the Surveyor General Quick-bird Satellite imagery 2006 Wetland & River system habitat transformation data as received from Dr Tom Bornman Department of Botany Nelson Mandela Metropolitan University as part of the Bitou Wetland Assessment Study. Literature review of the impact of low level aircraft movements on water birds Limitations & assumptions This study made the assumption that the above sources of information are reliable. The following factors may potentially detract from the accuracy of the predicted results: The SABAP data covers the period Bird distribution patterns fluctuate continuously according to availability of food and nesting substrate. (For a full discussion of potential inaccuracies in SABAP data, see Harrison, Allan, Underhill, Herremans, Tree, Parker & Brown, 1997). Phase 1 Predictive Scoping Study Page 5 of 29

6 The CWAC counts performed by BirdLife Plettenberg Bay are done biannually and as per the above assumption regarding the SABAP data the spatiotemporal fluctuations in bird distribution will influence the counts at a particular site. General comment: Predictions in this study are based on experience of these and similar species in different parts of South Africa. Bird behaviour can not be reduced to formulas that will hold true under all circumstances. Phase 1 Predictive Scoping Study Page 6 of 29

7 2 DESCRIPTION OF AFFECTED ENVIRONMENT 2.1 Topography & vegetation The wetland and salt marsh habitat present along the lower reaches of the Bitou River (the study area) has for many years been subjected to various impacts. The largest impacts have been in relation to the alteration of the hydrology of the system due to fresh water abstraction upstream. Other major impacts include agricultural activities with associated clearing of estuarine vegetation on the floodplains, construction of barricades across tidal channels, large scale residential developments and the release of treated sewerage effluent through the Ganse Spruit. The times at when these impacts commenced are outlined in the wetland assessment study (Bornman & Adams, 2006) but it would appear as if many of these impacts already started occurring before The presence of road bridges i.e. N2 has probably changed the plant community composition which in turn leads to changes in the intertidal invertebrate communities. This would have also changed the overall bird species diversity and their abundance. It is unlikely that changes as a result of the above impacts could be observed in the bird presence and abundance data received for the study area. Treated sewage from the Plettenberg Bay waste water treatment facility enters the Bitou Estuary system via the Ganse spruit. This adds a source of eutrophication to the Bitou system which in return could attract more birds to the Bitou River. Most of the treated sewage is cutrrently used to irrigate existing golf courses and polo fields and it is expected that this demand will grow (Bornman & Adams, 2006). All of the above could have contributed to changes in the available habitat for birds on the Bitou estuary and ultimately affecting their numbers and the species diversity found in the area. 2.2 Bird micro habitats It is necessary to look more closely at the habitats available to birds, i.e. the micro habitats, in order to determine where the relevant species will most likely occur in close proximity to the polo estate where the helicopter would approach at low level to land and take-off from. Investigation of this study area revealed the following bird micro habitats. Wetland and Salt Marshes: Wetlands are characterized by slow flowing water and tall emergent vegetation, and provide habitat for many water birds. The conservation status of many of the bird species that are dependant on wetlands reflects the critical status of wetlands nationally, with many having already been destroyed. A salt marsh is a type of marsh found in the intertidal transition between land and ocean. They are dominated by halophytic herbaceous plants. The water is saline, and both the water table level and salinity are dependent on tides. Salt marshes develop on depositional coasts where tidal action is relatively Phase 1 Predictive Scoping Study Page 7 of 29

8 gentle and erosion no more than intermittent and light enough to allow vegetation to take hold. They are common on low-energy coasts such as estuaries, enclosed bays, and the land sides of barrier islands and strips. Salt marshes are quite photosynthetically active and are extremely productive habitats. They serve as depositories for a large amount of organic matter, and are full of decomposition, which feeds a broad food chain of organisms from bacteria to mammals. In the study area, several areas of wetland and salt marshes were observed along the Bitou river supporting a wide diversity of water birds. Reed beds & sedges: Several areas of dense Phragmites reedbeds are present in the study area. Reed bed areas provide shelter, roosting and breeding space for certain water bird species. Dense growths of primarily bulrushes in the Ganse Spruit wetlands have encroached on open water areas in so doing reducing potential available habitat for water birds. Open water with submerged vegetation: Submerged vegetation, primarily Zostera is found in especially the lower reaches of the estuary. The submerged vegetation supports a rich diversity of organisms. Stands of alien invasive trees: Stands of alien trees e.g. Blue gums occur scattered through the study area. Such stands of trees, although alien, often provide roosting and breeding space for birds of prey i.e. the pair of fish eagles discussed in more detail later in this report. Rivers: A river is a large natural waterway. The Bitou River flows through the study area and is confined to the lower end, of a river is known as its base level where it spreads out into a meandering set of smaller streams through wetland and salt marsh areas in the estuary. Exposed mudflats Mudflats are coastal wetlands that form when mud is deposited by the tides or rivers, they are found in sheltered areas such as bays, bayous, lagoons, and estuaries. Mudflats may be viewed geologically as exposed layers of bay mud, resulting from deposition of estuarine silts, clays and marine animal detritus. Mudflats are typically important regions for wildlife, supporting a large population, although levels of biodiversity are not particularly high. They are often of particular importance to migratory birds. Mudflats are found in the study area but are more concentrated towards the estuary mouth. Phase 1 Predictive Scoping Study Page 8 of 29

9 2.3 Relevant bird populations Various data sources were used in determining the distribution and abundance of bird species in the study area: SABAP Data - TABLE 1 below shows a list of the Red Data bird species recorded in the study area and their report rates in the 3423AB quarter degree square (Harrison, Allan, Underhill, Herremans, Tree, Parker & Brown, 1997). Report rates are essentially an expression (%) of the number of times a species was seen in a square divided by the number of times that square was counted. A total of 25 Red Data species are listed. Nine Red Data waterbird species of relevance to this study are highlighted in the below table, the other Red Data Species are not likely to be impacted upon by the helicopter movement along the Bitou River. Table 1: Report rates of Red Data bird species in the 3423AB quarter degree square within which the study area falls (Harrison, Allan, Underhill, Herremans, Tree, Parker & Brown, 1997). No Name Scientific name Cons Status Reporting Rate (%) 3 African Penguin Spheniscus demersus V 5 17 Southern Giant-Petrel Macronectes giganteus NT 0 53 Cape Gannet Morus capensis V Cape Cormorant Phalacrocorax capensis NT White-backed Night-Heron Gorsachius leuconotus V 0 84 Black Stork Ciconia nigra NT 0 96 Greater Flamingo Phoenicopterus ruber NT 2 97 Lesser Flamingo Phoenicopterus minor NT Secretarybird Sagittarius serpentarius NT Martial Eagle Polemaetus bellicosus V African Crowned Eagle coronatus NT African Marsh-Harrier Circus ranivorus V Peregrine Falcon Falco peregrinus NT Lanner Falcon Falco biarmicus NT Blue Crane Anthropoides paradiseus V Denham's Bustard Neotis denhami V Greater Painted-snipe Rostratula benghalensis NT African Black Oystercatcher Haematopus moquini NT Chestnut-banded Plover Charadrius pallidus NT Black-winged Lapwing Vanellus melanopterus NT Caspian Tern Sterna caspia NT African Grass-Owl Tyto capensis V Half-collared Kingfisher Alcedo semitorquata NT Knysna Woodpecker Campethera notata NT Knysna Warbler Bradypterus sylvaticus V 0 Coordinated Waterbird Count (CWAC) data. The CWAC project aims to monitor populations of waterbirds by carrying out counts in summer and winter at various site across the country (Taylor, Navarro, Wren-Sargent, Harrison, Kieswetter, 1999). The lower Bitou and Keurbooms river estuary complex is regarded as one CWAC site and has been counted since the winter of The detailed waterbird count data was sourced from BirdLife Plettenberg Bay and included separate data for both the Bitou and Keurbooms Rivers. It must be noted that many non Red Data bird species also occur in the study area and will also be impacted on by the helicopter movement and can potentially pose a risk to the safe operation of the helicopter during low level flights. In particular the waterbird species included in the CWAC counts formed part of the study. Phase 1 Predictive Scoping Study Page 9 of 29

10 The above data sources, combined with the author s personal observations of habitat preferences will be used to assess the potential impact that the helicopter movement could have on the bird populations along the Bitou River and to proposed where possible mitigation measures. Phase 1 Predictive Scoping Study Page 10 of 29

11 3 PRELIMONARY PREDICTION OF INTERACTIONS AND IDENTIFICATION OF RISK SOURCES 3.1 Description of bird aircraft interactions It is estimated that bird and other wildlife strikes to aircraft annually cost the international aviation industry in excess of US$ 1 billion (Allan & Orosz, 2001). Furthermore, these strikes put the lives of aircraft crew members and their passengers at risk. Globally since 1990, bird and wildlife strikes have killed more than 157 people and destroyed over 140 aircraft (Richardson and West 2000; Thorpe 2003). The hazard of bird strikes are however not the only conflict between aircraft and birds. Aircraft overflights can cause disturbance to bird populations Potential disturbance caused by the helicopter movements Aircraft overflights can be an important source of disturbance for birds, resulting in behavioural changes (Lensink, van Eekelen & van Lieshout, 2002). Negative effects associated with such disturbance are increased energy consumption, lower food intake and resting time and in consequence and impaired body condition ultimately leading to potential population declines (Komenda-Zehnder, Cevallos & Bruderer, 2000). A literature review indicated that little research has been done to determine the effects of aircraft movements on waterbirds, particularly in South Africa. It is however also important to draw a distinction between the visual and auditory disturbance caused by overflying aircraft. The disturbance caused by overflying aircraft is therefore a complex combination of both visual and auditory effects. Loosjes (1974) indicated that birds reacted already to the noise of an approaching aircraft but only took flight when they could actually see the aircraft. Behavioural disturbance in birds is often however preceded by physiological indicators of stress such as increased heart rate (de Villiers & Giese, 2004). Studies on Dassen Island also indicated that African Penguins were susceptible to disturbance from approaching humans and showed physiological stress i.e. heart rate increases (de Villiers & Giese, 2004). The Swiss federal Office for Civil Aviation commissioned Komenda-Zehnder, Cevallos & Bruderer (2000) to conduct research in the Switzerland lowlands to determine a minimum flight altitude at which the negative influence of aircraft on the birds is negligible. Their analyses showed that helicopters have a higher potential for disturbance than fixed-wing aeroplanes and also confirmed such results from other earlier studies related to the disturbance caused by existing air traffic. They indicated that the proportion of birds with stressed behaviours was significantly higher during overflights below 300m for aeroplanes and below 450m for helicopters, than on days without flights. It can therefore be concluded that the minimum flight altitude that did not cause a change in behaviour of the birds was 450m above ground level (AGL) for helicopters. They also cautioned that birds might be more sensitive in undisturbed regions and when breeding. Reactions also varies between different bird families as Kempf & Hüppop (1995) demonstrated that Lapwings distribution and breeding was more related to habitat structure than by the effects of air traffic. Their Phase 1 Predictive Scoping Study Page 11 of 29

12 research did however also conclude that helicopters had more of an effect on birds than fixed wing aircraft. It is most important to note that all literature with regard to the impacts of helicopters on sea and shorebirds relates to direct disturbance caused by the presence of the helicopter (birds seeing the helicopter as a threat in their environment) and due to the noise generated which frightens birds (Blaine, Ryan & Nel, 2002). Most of the studies however focussed on the short term effect of aircraft or helicopter overflights. Perhaps the most persuasive evidence that this is a concern comes from the decline and subsequent recovery in the population size of Adélie Penguins breeding at Cape Royds, Antarctica, following the cessation of helicopter landings and overflights close to the colony in (Thomson 1977, Fraser & Patterson 1997). However, disturbance at this colony was not limited to helicopters, and so the decline cannot be attributed entirely to helicopter operations as these other disturbances were also stopped in Also, the intensity of disturbance prior to 1963 was apparently fairly high. Elsewhere there is at least some evidence of birds habituating to aircraft (WBM Oceanics Australia & Claridge 1997), but we lack the ability to predict whether species will become habituated, and if so, what level of disturbance is required. African Penguins at Boulders clearly tolerate high levels of human disturbance, probably through habituation but perhaps also selection for more tolerant birds (Fowler 1999). However, we lack the ability to predict whether species will become habituated, and if so, what level of disturbance is required. Also worthy of note is that the helicopter movements at the Bitou is of a temporal nature i.e. only in the Polo Season during April and December. From the above it can be concluded that helicopter flights below 450m / ca ft (AGL) will result in some level of disturbance to birds. The extent of the disturbance can however not be quantified at this stage as detailed observations would need to made during the proposed phase two of the study Risk of bird strikes during low level helicopter flights The International Civil Aviation Organisation (ICAO) maintains a database of bird strike occurrences and an analysis of the bird strike data indicated that 58% of the incidents occurred below 100 ft and 74% of all incidents below 2500 ft (AGL). Less than 1% of reported incidents were with helicopters (ICAO, 1994). The US Bird Strike Committee ( reports that on 30 December 2005 a Bell 206 Pilot flying at 500 feet AGL near Washington, struck a large vulture which crashed into the windshield. The pilot was temporarily blinded by blood and wind. After regaining control, the pilot tried to land in a bean field nearby but blood was hampering his vision and the left skid hit the ground first causing the aircraft to tip on its side. Pilot was taken to the hospital and had several surgeries to repair his face, teeth and eye. The helicopter was damaged beyond repair. Cost of repairs would have been $1.5 million. En-route bird strike occurrences are of particular concern especially for low level operation, e.g. military training operations. Various fatal bird strikes with military aircraft have occurred during such low level operations (Richardson & West, 2000). Helicopters are often used to conduct power line inspections. Various birds of prey are known to nest on transmission power line towers in South Africa (Jenkins, de Goede & van Rooyen, 2005). During routine inspection flights along these power lines the following responses have been noted as a result of the approaching helicopter into the nesting territory of the birds. Martial Eagles (Polemaetus Phase 1 Predictive Scoping Study Page 12 of 29

13 bellicosus) are visibly disturbed by the helicopter, often taking evasive action, or lying flat on the nest structure. Black Eagles (Aquila verreauxii) are less affected but often also fly off the nest. Tawny Eagles (Aquila rapax) however react extremely aggressive towards the helicopter and often fly directly towards it in an attempt to scare it threat away (van Rooyen, pers. comm.) Tawny Eagles are in general very aggressive birds of prey and often scavenge or pirate food from other birds of prey (Hockey, Dean & Ryan, 2005). African Fish Eagles (Haliaeetus vocifer) are also described as scavengers who often steal prey from other raptors and they are extremely territorial, especially within their nesting territory (Hockey, Dean & Ryan, 2005). It can therefore be expected that Fish Eagles could at the height of the breeding season respond similarly towards an approaching helicopter. Concern is therefore noted regarding the proximity of the existing helicopter hanger on the polo estate to the stand of tall pine trees where a pair of fish eagles used to nest. Discussions with Cape Nature (G. Shaw, pers. Comm.) and staff from the South African Air Force at both the Langebaanweg Air Force Base as well as the Test Flight & Development Centre (TFDC) between Bredasdorp and Arniston indicated that they either follow a no fly zone approach over sensitive wetland areas e.g. De Hoop Vlei, Berg River Estuary, Langebaan Lagoon etc. Such measures are taken to minimise the risk of bird strike during low level flights in these regions or in response to declare no fly zones to limit disturbance to protected areas Existing helicopter operations along the Bitou River and Keurbooms River. Helicopter operations are already in existence within the study area. These activities mostly take place during the month of April, November, December and January. Several private helicopters are then in operation in the area. The helicopter at the Polo Estate is used either to transport guests in and out of the estate and / or to do scenic flights around the area. To date no concerns have been noted regarding nearmisses with birds during these flights. Figure 1: The private helicopter which operates from the Polo Estate Phase 1 Predictive Scoping Study Page 13 of 29

14 4 BIRD POPULATION ASSESSMENT In order to best evaluate the bird populations which can be potentially affected by the helicopter movements and vice versa, emphasis was placed on waterbirds. Specific species of concern with a high probability of being impacted upon was dealt with in more detail. 4.1 CWAC Counts CWAC counts have been done on the Bitou and Keurbooms River sites since the winter of 1995 (Appendix 1). CWAC Counts are performed biannually and the timing of the counts in the middle of their respective seasons to avoid periods of passage by migratory species and therefore the counts reflect periods of relative stability (Taylor, Navarro, Wren-Sargent, Harrison & Kieswetter, 1999). A total of 57 and 59 species have been recorded on the Bitou and Keurbooms Rivers respectively. 82 species were recorded on the combined Keurbooms Bitou River system. CWAC data were analysed over time to observe trends in species diversity and total bird counts on the Keurbooms and Bitou respectively. In addition to also better understand the carrying capacity of the wetland analyses was performed looking at the total biomass of birds present on the wetland the total biomass is the number of individuals per species multiplied, respectively, by the average mass of an individual of each species, summed across all species. These three variables (species diversity, total count and total biomass) can be used as indicators of the quality of the wetland as a whole. Species diversity is an indication of the diversity and quality of available habitats. The total count and biomass indicate the quantity of useable habitat and the carrying capacity of that habitat. Total count and biomass should be viewed in conjunction because fluctuations in numbers may not necessarily indicate changes in carrying capacity if biomass is relatively constant, and vice versa (Taylor, Navarro, Wren-Sargent, Harrison & Kieswetter, 1999). Rainfall data for Plettenberg Bay was also included to demonstrate any correlations that there might be between total annual rainfall and respective bird counts. It should however be noted that the bird counts, as described above, were done on a biannual basis and significant rainfall events for a particular year could have taken place after the respective summer or winter counts took place therefore making it difficult to correlate the CWAC data with rainfall data. Figure 2: A view of the Bitou River in front of the Polo Estate Property. Phase 1 Predictive Scoping Study Page 14 of 29

15 45 Rainfall Summer Winter Linear (Summer) Linear (Winter) Species diversity R 2 = R 2 = Average Annual Rainfall (mm) Figure 3: Keurbooms River species diversity. Species diversity has remained rather constant over time with some annual fluctuations correlated with rainfall Rainfall Summer Winter Linear (Summer) Linear (Winter) Total number of individual birds R 2 = Average Annual Rainfall (mm) 500 R 2 = Figure 4: Keurbooms River total count of individual birds. Trend analysis did not indicate any definitive trend with high reliability although there appears to be a downward tendency. There also appears to be some correlation between total bird numbers and rainfall as numbers tend to be higher during both winter and summer counts when there has been a high annual rainfall recorded. Phase 1 Predictive Scoping Study Page 15 of 29

16 1200 Rainfall Summer Winter Linear (Summer) Linear (Winter) Total Biomass (kg) 600 R 2 = R 2 = Average Annual Rainfall (mm) Figure 5: Keurbooms River total biomass. Again no definitive trend with high reliability could be detected but less of a downward tendency is observed. There however appears to be a closer correlation between biomass and total annual rainfall. 45 Rainfall Summer Winter Linear (Winter) Linear (Summer) Species Diversity R 2 = R 2 = Average Annual Rainfall (mm) Figure 6: Bitou River waterbird species diversity. Species diversity on the Bitou river seems to be closely correlated to total annual rainfall but has decreased slightly over time. No definite trend could however be detected from the data. Phase 1 Predictive Scoping Study Page 16 of 29

17 Rainfall Summer Winter 800 Linear (Winter) Linear (Summer) 700 Total number of individual birds R 2 = R 2 = Average Annual Rainfall (mm) Figure 7: Bitou waterbird total count. Again the total individual bird numbers seems to be closely correlated to rainfall along the Bitou River. The linear trend for both summer and winter counts indicate a downward linear trend but with low reliability as a result of the fluctuations observed in the data which correlates more closely with rainfall Rainfall Summer Winter 800 Linear (Summer) 600 Linear (Winter) 700 Biomass (kg) 400 R 2 = R 2 = Average Annual Rainfall (mm) Figure 8: Bitou waterbird total biomass. Again there seems to be a correlation between total annual rainfall and carrying capacity of the Bitou River wetlands. Trend analysis did not indicate any reliable observed tendencies. The above data analysis also indicated that there is no seasonal preference by birds for the wetlands of either the Bitou or Keurbooms rivers. It can therefore be deduced from the CWAC data that the presence and diversity of birds on the wetlands are largely determined by water levels and associated available habitat. There is however no clear trend that emerges from the CWAC waterbird counts and it would therefore not be reliable to use this data in order to evaluate or predict the effects of one the helicopter movements over the study area or two any other anthropogenic or natural disturbances. Phase 1 Predictive Scoping Study Page 17 of 29

18 4.2 Specific species of concern Despite the potential impact that the helicopter movements could have on all waterbird species along the Bitou and Keurbooms rivers and estuary it was considered prudent to consider the following bird species in terms of their conservation significance and potential risk to the safe operation of the helicopter in more detail Blue Crane (Anthropoides paradiseus) A pair of Blue Cranes, conservation status vulnerable (Barnes, 2000), is known to occur along the lower reaches of the Bitou River. The cranes are regularly observed on the Stanford Polo estate and the birds nested on the property during the 2005/2006 breeding season (Polo Estate Manager, pers. comm.). The adult cranes with their young were observed on the property during the site visit in June Figure 9: The adult pair of Blue Cranes with two fledglings observed on the Polo Estate during the site visit in June Discussions with Birdlife Plettenberg Bay indicated that this is currently the only pair of Blue Cranes known to occur in the area. Special attention should therefore be given so as to not disturb these birds especially during the breeding season, August April with an egg laying peak during November in South Africa (Hockey, Dean & Ryan, 2005). Uncertainty exists with regard to where exactly the cranes bred during the 2005 / 2006 breeding cycle as eggs were observed in one of the horse paddocks but the estate manager could not confirm whether the birds hatched those eggs or whether they re-laid elsewhere. Observations during the 2007 breeding season indicated that the Blue Cranes were once again successful breeding and hatching two chicks on the property (see figure below) Phase 1 Predictive Scoping Study Page 18 of 29

19 Figure 10: The adult pair of Blue Cranes with two fledglings observed on the Polo Estate during April African Fish Eagle (Haliaeetus vocifer) Several pairs of African Fish Eagles are known to occur along the Bitou and Keurbooms Rivers (B. Denman, pers. comm.). The resident pair along the lower reaches of the Bitou River used to nest in a stand of tall pine trees on the Stanford Polo Estate some 150m away from the helicopter hangar. The birds have subsequently moved their nest 1.2km away to a cliff face on the opposite side of the river and wetland area. Figure 11: Location of the previous nest site of the African Fish Eagles in comparison to the Polo field and the new nest site some 1.2km away on the opposite side of the wetland. Phase 1 Predictive Scoping Study Page 19 of 29

20 Figure 12: Location of the previous nest site of the African Fish Eagle pair on the Polo Estate in relation to the helicopter hangar which is approximately 150m away. Figure 12: Location of the previous nest site of the African Fish Eagles in the tall pine trees on the Polo Estate. Pairs often use the same nest year after year, or in some cases they have several (2-5) nest sites that they use in rotation (Hockey, Dean & Ryan, 2005). The breeding season usually starts around March April when pairs start nest building or refurbishing an existing site. It usually takes them a few weeks to refurbish an existing nest site. 1-4 Eggs are usually laid during May or June in South Africa. After an incubation period of days the chicks remain on and around the nest for days before their first flight, usually only 1 or two chicks fledge successfully depending on availability of food (Hockey, Dean & Ryan, 2005). The entire breeding cycle therefore usually last from April until August / September when the young have fledged and become independent. 4.3 Evaluation in terms of Ramsar criteria The Convention on Wetlands, signed in Ramsar, Iran, in 1971, is an intergovernmental treaty which provides the framework for national action and international cooperation for the conservation and wise use of wetlands and their resources. There are presently 152 Contracting Parties to the Convention, with 1610 wetland sites, totalling million hectares, designated for inclusion in the Ramsar List of Wetlands of International Importance. The Ramsar Convention's mission is the conservation and wise use of all wetlands through local, regional and national actions Phase 1 Predictive Scoping Study Page 20 of 29

21 and international cooperation, as a contribution towards achieving sustainable development throughout the world (Ramsar, 2006). Ramsar lists criteria for Identifying Wetlands of International Importance. Group B of the criteria deals specifically with sites of international importance for conserving biodiversity and criterion 5 and 6 are specific criteria based on waterbirds: Criterion 5: A wetland should be considered internationally important if it regularly supports 20,000 or more waterbirds. Criterion 6: A wetland should be considered internationally important if it regularly supports 1% of the individuals in a population of one species or subspecies of waterbird. According to Taylor, Navarro, Wren-Sargent, Harrison & Kieswetter (1999) the CWAC data collected during indicated that the Keurbooms River Estuary supports 1% of the estimated global population of the Kelp Gull Larus dominicanus and at least 0.5% of the estimated Global population of the Swift Tern Sterna bergii. The Bitou River did however not feature in terms of supporting at least 1% of the global population of any waterbird species. In terms of the interconnectedness of the Bitou and Keurbooms River systems the conservation and management of these two rivers should be considered holistically. Turpie, et. al. (2002) rated the Keurbooms River Estuary 16 th in terms of overall conservation importance. Their study also rated it 7 th in terms of bird conservation importance! Therefore based on the importance of the Keurbooms / Bitou River systems and estuary and the fact that the Keurbooms estuary supports at least 1% of the population of a waterbird species/s there is a good case for elevating its conservation and Ramsar status. It should however be noted that the Keurbooms / Bitou River system does not support in excess of waterbirds at any one time. 4.4 Cumulative impact assessment Residential developments is a critical threat, while boating, fishing and general human disturbance, domestic animals and bank erosion are listed as sever threats to the Keurbooms river estuary. Similarly they list pollution from effluent, pesticides and fertilizers, and damage by livestock, siltation, reed encroachment and residential development as critical threats to the Bitou River (Taylor, Navarro, Wren-Sargent, Harrison & Kieswetter, 1999). The proposed use of treated sewerage water for irrigation at the Hanglip Golf course will not negatively affect the Ganse Spruit as long as a sufficient flow of water can be maintained through the wetland. The reduction in nutrients could in addition result in more open water areas over time. Possibly creating a greater diversity of habitat types attracting more birds of different species. The wetland assessment study also highlighted that the Bitou / Keurbooms estuary system has been exposed to various forms of anthropogenic disturbances over the past few decades all of which would have had an impact on the bird presence and species diversity on the estuary. Taking into account when most of the significant Phase 1 Predictive Scoping Study Page 21 of 29

22 human induced changes were brought about in the system, pre 1961 (Bornman & Adams, 2006) it would be reasonable to assume that significant changes could then have already occurred in the presence an abundance of bird species. No bird presence and abundance data is however available from those days making it impossible to assess the effect which those habitat alterations had on bird diversity an abundance at the time. The effects of these impacts are however also of an ongoing nature and the pressures on the estuary continue to increase. Given the extent to which human related activities have impacted upon the lower reaches of the Bitou / Keurbooms Estuary special attention must be paid to minimising further negative disturbance which in turn could negatively affect bird diversity and abundance. Phase 1 Predictive Scoping Study Page 22 of 29

23 5 RECOMMENDED MITIGATION MEASURES The following are recommended mitigation measures for the impacts identified and discussed above. Although the CWAC data does not demonstrate a definite decline in waterbird numbers or biomass it is a reasonable assumption to make given the evidence presented regarding the effect that aircraft movements have on waterbirds that the operation of helicopter and other fixed wing aircraft over the Bitou and Keurbooms Rivers would have a negative impact on the bird population. Taking a precautionary approach it is therefore suggested that a minimum flying altitude be instigated over the Keurbooms and Bitou Rivers of at least 450m (AGL) (ca ft) in order to minimise the effect that such aircraft movements could have on waterbirds. Figure 13: Outline of proposed of minimum 450m (AGL) overflight zone over the Bitou and Keurbooms Rivers to minimise potential impacts on waterbirds. The resident pair of Fish Eagles will in all likelihood start investigating potential nesting sites for the 2007 breeding cycle during March / April In order to determine if the birds would again consider using the previously abandoned site in the tall trees on the Polo Estate it is recommended that no helicopter movements be allowed in the close proximity of the hangar during March / April of The situation must then be monitored to asses if the birds are showing an interest to return to this alternate nest site. Should the birds return to this site care should in future be taken to never fly the helicopter in a 300m radius around the site during the entire breeding season of the Fish Eagles i.e. March to September. Helicopter movements in this area could then only be considered during the nonbreeding season. Phase 1 Predictive Scoping Study Page 23 of 29

24 Figure 14: Fish Eagle nest site in relation to the hangar and proposed helicopter movement exclusion zone around nest site to minimise disturbance to the birds during the breeding season. Consideration should also be given to the resident pair of blue cranes on the estate. Disturbance around the nest site should be prevented. If the birds are found to have laid eggs in a horse paddock usage of that particular paddock should be suspended until such time as the cranes chicks have hatched and they are moving around with the adult birds approximately one day after hatching (eggs are incubated for approximately 30 days) (Hockey, Dean & Ryan, 2005). Design of monitoring study to document/ capture data on interaction between birds and helicopter - December 2006 / April 2007 In order to better assess the effect of the helicopter overflights on the waterbirds present on the Bitou and Keurbooms River it is proposed that the phase two of the study still be undertaken but that the following amendments be considered. In light of the methodology used by Komenda-Zehnder, Cevallos & Bruderer in 2000 it is suggested that the phase two study to determine the actual impact of the helicopter overflights on the waterbird populations be altered. Fixed observation points should be used and the observer should asses the responses of the birds to the helicopter overflight 5 minutes before, during and 5 minutes after the overflight. Such observations can be undertaken during one site visit when the helicopter movements are taking place. Another site visit is then recommended during April 0f 2007 to assess the situation with regard to the pair of Fish Eagles and attempt to asses their activity around their alternate nest sites in particular the previously used nest site on the polo estate. Phase 1 Predictive Scoping Study Page 24 of 29

25 6 CONCLUSION The lower reaches of the Bitou and Keurbooms River forms a unique estuarine system supporting a wide variety of habitat types and a rich diversity of bird species. The study concluded that low flying aircraft and or helicopter movements are likely to have a negative effect on bird behaviour, albeit for a sort period during the actual activity only. Little research has however been done to evaluate the long terms effects of low flying aircraft on bird populations. The temporal nature of the propose helicopter movements (i.e. April and December) would also negatively affect potential habituation over a longer period of time. A real risk also exists in terms of experiencing a bird strike during low flying operations, especially so taking into consideration the potential aggressive behaviour from birds of prey i.e. the Africa Fish Eagles known to have bred in close proximity to the helicopter hangar. An analysis of CWAC data collected since 1995 indicated that there is no seasonal preference by birds for the wetlands of either the Bitou or Keurbooms rivers. It can therefore be deduced from the CWAC data that the presence and diversity of birds on the wetlands are largely determined by water levels and associated available habitat. There is however no clear trend that emerges from the CWAC waterbird counts and it would therefore not be reliable to use this data in order to evaluate or predict the effects of one the helicopter movements over the study area or two any other anthropogenic or natural disturbances. A pair of Blue Cranes and a pair of Africa Fish Eagles are known to have nested on the polo estate and particular care should be taken not to disturb these birds. Although the Keurbooms / Bitou River systems and estuary does not support in excess of waterbirds the fact that the Keurbooms estuary is of high conservation significance and that it supports at least 1% of the population of a waterbird species/s (Kelp Gulls) there is a good case for elevating its conservation and Ramsar status. The study concludes to recommend that a minimum flying altitude of at least 450m (AGL) (ca ft) be instigated over the Keurbooms and Bitou Rivers of in order to minimise the effect that low level aircraft movements could have on waterbirds. The presence and interest to again nest there of the pair of Africa Fish Eagles on the polo field property should be further investigated. If the birds are found to gain be interested in using the existing nest helicopter flights should be restricted to the non-breeding summer months. Given the unique diversity both in terms of habitat and birds every effort should be made to conserve the Keurbooms / Bitou River systems and estuary. Phase 1 Predictive Scoping Study Page 25 of 29