Browsing by Author "Thomson, Robert"

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    An investigation into the root of two of the main vulture threats: poisoning and belief-based use of vulture body parts in Southern Kenya
    (2023) Sekyanzi, Joseph; Thomson, Robert
    Vultures are crucial scavengers, removing carcasses, and maintaining the healthy and clean environments. However, their populations are rapidly declining. Six of eight Kenyan vulture species are currently listed as ‘Endangered' or ‘Critically Endangered' on the IUCN Red List. Poisoning caused by human-wildlife conflicts is a major threat to vultures after belief-based use of their body parts. A total of 1387 interviews were administered within Maasai Mara pastoral community. We used the ‘Unmatched Count Technique' to estimate the prevalence and distribution of poison use, and direct questions to characterize poison types, usage and sources, as well as belief-based use of vulture body parts. We found that 54% of respondents reported Carbofuran poison, whereas nearly half (48%) of respondents pointed to agrovets as a major source of all poisons and popularly (84%) smeared on carcasses. The vast majority (75%) particularly use vulture feathers for arrows. Further, 22% fence off their livestock against predatory wildlife. We further explored how predation protection measures used predict individual poisoning likelihoods. None of the five main predation protection measures significantly influences poison use. Both fencing and the use of lights as predator control measures attenuate the poisoning risk. However, herding indicated weak signals for poison use amongst pastoralists. We proposed that an effective vulture poisoning risk reduction should be multi-faceted and collaborative. Regulating and monitoring of the import, local trading and use of poisonous substances. Building partnerships and engagements for more support for local livelihoods. Lastly, upscaling fencing and expanding the communal conservancies. These strategies would curb retaliatory human-wildlife conflicts and poison use against wildlife and vultures in Southern Kenya.
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    Assessing the anthropogenic threats to vultures in the communal farmlands of Namibia
    (2017) Craig, Christie; Thomson, Robert; Santangeli, Andrea
    The use of poison by farmers to control livestock predators is a major threat to vulture populations across Africa. In Namibia, there is now some understanding of poison use on commercial farms, but the situation in the communal farmlands is still poorly understood. Using a series of 36 questions, I interviewed 367 communal farmers to assess the prevalence of poison use across the north-west, north and eastern communal land. I found that 18% (SE 2.8) of farmers had killed a predator in the last year and 1.7% (SE 2.1) used poison to do so. I mapped the probability of poison use across the communal regions surveyed and found that poison use is predicted to be higher (up to 7% of farmers using poison) in some areas of the upper north-west. In contrast to previous research, those living adjacent to protected areas did not experience greater losses to predators and as a result were not more inclined to use poison. I found that those using poison are more likely to own greater numbers of livestock, particularly large livestock. Overall, my study suggests that poison use is approximately 12 times lower in the communal areas than on commercial farms. A number of farmers expressed that it is dangerous to use poison on communal land as the risk of non-target impacts is much higher where the land is not fenced and is communally used. Nonetheless there are communal farmers who are using poison and this poses a risk to already threatened vulture populations. Lastly, I did a survey to look at the farmers' local knowledge about vultures, their attitudes towards them and any cultural value that vultures hold. Overall vultures were viewed positively by farmers. The cultural use of vulture parts appeared fairly uncommon, with 9.5% of farmers reporting that they knew of uses. Many farmers indicated that the cultural use of vulture parts was something practiced by previous generations. Feathers were the most commonly used part, mainly for decorations and making arrows. From my assessment, it appears that anthropogenic threats to vultures in communal areas are fairly low. The cultural use of vulture body parts is rare. In addition, poison is used but this practice is not nearly as common as it is on commercial farms. Since poison can have such devastating impacts on vulture populations, I nonetheless advise that reactive and preventative measures are put in place to reduce poisoning and minimise the impact when poison is used. The identified 'hotspots' of poison use will assist local authorities to focus their poison mitigation efforts.
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    Breeding and dispersal implications for the conservation of the Southern Ground Hornbill Bucorvus leadbeateri
    (2017) Carstens, Kate; Ryan, Peter G; Little, Rob M; Thomson, Robert
    Populations of secondary tree-cavity nesting bird species are often limited by a shortage of natural nesting sites. For the Southern Ground Hornbill Bucorvus leadbeateri that typically nests in natural tree cavities, the shortage of nesting sites is one factor potentially limiting population growth. The species is listed as endangered in South Africa, and vulnerable throughout the rest of its range. Nest boxes can improve the conservation status of threatened birds that are limited by nest-site availability. However, nest boxes or other types of artificial nests are not always beneficial to the target species, and their value as a conservation tool needs to be tested for each species. Wooden nest boxes were installed for ground hornbills in a study area in north eastern South Africa with a paucity of natural nest sites. In this thesis, I assess productivity, timing of breeding, and dispersal in the Southern Ground Hornbill in a study area supplemented with nest boxes and discuss the implications for the conservation of this endangered species. Nest boxes are an effective conservation tool to improve productivity in areas lacking natural tree cavity nesting sites. Breeding success (calculated as the proportion of nesting attempts that fledged a chick) and predation levels were similar for groups using nest boxes and natural nests. Natural nests were more buffered against cooling night temperatures, but otherwise nest boxes provided nesting conditions that were no better than natural nests. Timing of breeding for nests in natural tree cavities and nest boxes were similar. However, groups with access to a nest box attempted breeding more often than groups with access to a natural nest only, resulting in an 15 % increase in the number of fledglings per group compared to an adjacent protected area with no artificial nests. The number of breeding groups in the study area increased by 460 % over 12 years. However, there is a limit to the density of breeding groups. Breeding success was highest when breeding density was one breeding group per 90-120 km², so nests should be spaced ~10 km apart. Given that the threats to ground hornbills include persecution and poisoning, increasing the reproductive rate by providing nest boxes should assist in slowing the decline by the increased recruitment of offspring into the population. Timing of breeding varied across years. The first eggs laid each year ranged from 9 September to 14 November, and median lay date was 03 November. Breeding attempts that were initiated early in the season were more likely to fledge a chick than those initiated later in the season. Timing of breeding was delayed during warmer springs, particularly under dry conditions. In savannas, hotter spring temperatures could limit food availability, for example, if higher temperatures cause the vegetation to dry out, resulting in a rapid decline in insect flush, especially in the phytophagous insect groups that form a large part of the ground hornbill diet. Factors to consider when constructing and placing nest boxes include thickness of the cavity walls, entrance height above ground and density of nest boxes placed in the landscape. Breeding attempts in natural nests and nest boxes with thicker nest walls and those positioned with higher entrances above the ground increased breeding success. Therefore, nests should be constructed with cavity walls at least 6 cm thick and placed so that the entrances are situated > 6 m above the ground. With 186 ringed chicks fledging from the study area after the installation of nest boxes, it was possible to observe their dispersal within the study area and farther away into the adjacent Kruger National Park. There was no evidence for sex-biased dispersal. Males and females dispersed at similar ages, and over similar distances, raising interesting questions about inbreeding avoidance mechanisms in this species. If females do not disperse beyond the range of related males, how do related individuals avoid pairing, and what forms of individual recognition exist?
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    Disturbance effects of boat-based tourism on waterbirds at the Ramsar-designated De Hoop Vlei, Western Cape, South Africa
    (2017) De Blocq Van Scheltinga, Andrew; Ryan, Peter G; Thomson, Robert
    Recreation and ecotourism activities are growing in demand worldwide, especially in biodiversity hotspots. Protected area managers may seek to introduce novel activities in order to generate revenue. However, disturbance effects brought about through encounters between humans and wildlife can have negative consequences, which conflict with conservation goals. De Hoop Vlei is a large coastal lake within the De Hoop Nature Reserve. It is a Ramsar site as well as a key feature of a BirdLife Important Bird Area (IBA). Proposals for motorized boat tours and kayak tours on the vlei have been made, for which this study provides an impact assessment. Repeated counts were performed in order to characterize the waterbirds present during the high water level conditions required for boating. Birds were concentrated in areas with aquatic vegetation and shallow water, mainly along the vlei's western shoreline and southern and northern ends. Two routes were designed for boat tours that would minimize disturbance by avoiding these areas as well as breeding sites. Count data were also used to revise the Ramsar and IBA assessments, which underestimated the site's conservation value. Boat tours were monitored to estimate the number of birds disturbed, and to measure agitation distances (ADs) and flight initiation distances (FIDs) in response to the boat as well as a kayak. Post-disturbance recovery was investigated, as was the likelihood of habituation using a space-for-time substitution at a site with regular boat traffic. Boat tours did not typically disturb more than 10% of birds present at the vlei, and largely avoided disturbing species of conservation concern. Responses to the kayak were more severe than to the boat, which is most likely due to the similar speeds of the two boats are similar and the kayak is more easily perceived as a threat due to its shape and stealth, the presence of a paddler, and the consistent paddling motion. Post-disturbance recovery of species was slow and incomplete after an hour, meaning that there are likely costs for foraging opportunities and breeding if important areas are disturbed. Most species did allow a closer approach at the site with regular boating, but AD did not differ between them for most species. From these results it would be dangerous to assume that habituation will mitigate against disturbance impacts. Recommendations made included that kayak tours should not be permitted. Boat tours, with correct management, can be conducted in a manner that will not be too disruptive to birds. This study is the first to document such a large difference in responses of birds to two differing boat types, and is a rare example of disturbance of birds being studied in an African context.
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    Land use and breeding ecology of a renosterveld endemic bird: the Agulhas Long-billed Lark Certhilauda brevirostris
    (2023) Rose, Sanjo; Thomson, Robert; Lee Alan
    Agricultural expansion and intensification are among the leading contributors to biodiversity loss. Ground-nesting birds are especially vulnerable. Understanding the distribution and nesting requirements of a species is important, particularly if that species exists almost entirely within a human-modified landscape. The Agulhas Long-billed Lark Certhilauda brevirostris is a mediumsized passerine endemic to South Africa's Overberg region, an area extensively cultivated for crops and livestock production. The aim of this study was two-fold: to better understand patterns in landscape occupancy of this species as related to a set of biotic and abiotic variables, and to investigate the breeding ecology of this lark. To investigate the first question, I conducted 10–minute point counts at 51 sites regularly spaced in the core distribution of Agulhas Long-billed Lark. Points were spaced along small rural roads quarterly between October 2020 and January 2022. Agulhas Long-billed Larks were recorded at 58% (n=204) of 351 counts. Occupancy models were used to determine how detection was related to survey variables (temperature, wind speed and start time). Occupancy was then modelled against site variables (percentage renosterveld and riverine vegetation, and amount and type of fence line vegetation). Detection probability was estimated to be 0.67, giving an occupancy probability at sample sites of 0.91. Detection was negatively correlated with an increase in wind speed and temperature. Agulhas Long-billed Lark occupancy was greater when there was more renosterveld within a 250 m radius of the point count. It was positively associated with renosterveld along fence lines and a combination of renosterveld and riverine vegetation. To investigate the breeding ecology of this lark, extensive field visits over two years were conducted to establish baseline breeding ecology data. Over two nesting seasons, 29 Agulhas Long-billed Lark nests were found. Nesting started in winter (July) and continued until mid- summer (December). Most nests (66%, n=19) were in renosterveld with the remainder in human-modified landscapes. Nests were a shallow cup placed on the ground, wellconcealed at the base of a small bush or grass clump. Nests were monitored using video footage obtained from camera traps. The mean clutch size was 2.7 ± 0.5 (SD; median=3, range 1–3, n=20). Only the female incubated (n=10), and the incubation period was 16 days (n=1). The mean number of chicks hatched was 1.9 ± 0.8 (median=2, range 1–3). Two chicks fledged 13 and 17 days after hatching. Both sexes provisioned chicks. Provisioning rate was related to chick age and time of day but not brood size. Nesting success was low, with only 14% of broods fledging. Predation was the main cause of nest failure, with eight species of nest predators identified. A preference for nesting in renosterveld highlights the need for protection of this endangered habitat type. Although apparently well-adapted to this transformed landscape, the occupancy and breeding ecology results indicate that certain landscape features need to be preserved and that Agulhas Long-billed Lark will not be immune to unchecked land use change, especially given that, as a range-restricted endemic, the lark has limited displacement options.
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    Sociable weaver nests as a resource to local animal communities
    (2020) Lowney, Anthony; Thomson, Robert
    Animal space use in a landscape generally depends on resources. Facilitation by other species may impact resource availability that can positively influence local species diversity and community structure. Species that significantly change resource availability are often termed ecosystem engineers. The challenge here, is not only to document engineers that disproportionately influence ecosystems but also to determine their consequences to communities. I aim to understand the importance of a potential ecological engineer in a desert ecosystem to animal species diversity and community structure. I investigate how the role of this engineer may change with environmental harshness, and further examine specific associations and interactions with the host engineer. Sociable weavers (Philetairus socius) are a colonial passerine endemic to the semi-arid and arid Kalahari in the western parts of southern Africa. This species builds massive colonies that appear to form a focal point for the animal community in this system, and some species are known to show strict or strong associations with the colonies. Weaver colonies appear to be a resource to other animals in the environment, with food and nutrients clumped at colonies, and even thermal benefits available to occupants (a potentially crucial resource in arid environments). Nevertheless, the full importance of nest colonies to the surrounding animal community is still unknown. The main aims of this thesis were to determine the importance of Sociable weaver colonies to the surrounding animal communities and how this importance may change as environment harshness changes. To understand this, I investigate the use of colonies by multiple taxa (mammals, birds, reptiles and invertebrates) across seasonal and spatial aridity gradients. An additional aim is to describe the nature of the interactions between Sociable weavers and their associates. Therefore, determining how multiple species can access the colony resources at the same time and further, understand how these associates may impact the weavers. Here, I consider the interactions between Sociable weavers, Kalahari tree skinks (Trachylepis spilogaster), African pygmy falcons (Polihierax semitorquatus) and snakes. These species have all been shown to associate with weaver colonies and may impact weavers and each other in different ways. I show that Sociable weaver colonies create localised biodiversity hot-spots. These strong associations of multiple taxonomic groups which characterises their entire range and suggests a high importance of weaver colonies for the whole surrounding animal community. Although no variation was observed across a seasonal gradient, colony trees were associated with a greater abundance of animals at sites with lower rainfall, whereas sites with higher rainfall had a more evenly distributed abundance of animals between colony and non-colony trees. Additionally, I set out to describe the nature of the interactions between Sociable weavers and their recognised close associates. Through a series of observational and experimental studies I demonstrate that Kalahari tree skinks can eavesdrop on weaver alarm calls, this likely permits them to manage their predation risk and facilitate their coexistence with a predator, the pygmy falcon, at weaver colonies. The ability to eavesdrop also allows skinks to access riskier foraging habitat, thus, expanding their realised niche. Furthermore, pygmy falcon's defensive behaviour appears to deter predatory snakes from accessing a given colony. However, weaver reproductive output did not improve at falcon hosting colonies, suggesting falcon protection was offset by their predation of weaver chicks. Falcons saw an increase in nest predation when weavers were breeding, due to an increase in snake activity at colonies. When weavers were not breeding, falcons were more likely to fail, because of reasons other than predation (lack of provisioning, abandonment). This all demonstrates that weavers are clear-cut obligate ecosystem engineers, and one that can reduce stress that may allow species to persist in an environment that is predicted to become more harsh, due to global climate change. Furthermore, interactions at colonies demonstrate costs and benefits for weavers and their close associates, suggesting that a complicated ecological web of interactions allow these species to coexist.
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    The costs and benefits of hosting colonial sociable weaver nests for arid zone savanna trees
    (2023) Aikins, Khan Timothy; Thomson, Robert; Cramer Michael
    The savanna ecosystem is water and, in some instances, nutrient-limited, creating competition among species. Species, however, coexist in this ecosystem through processing like facilitation acting together with competition. Facilitation is an ecological interaction in which one species enhances the habitat of another species. Research on facilitative interactions between birds and plants has mainly focused on pollination and seed dispersal, but many birds interact closely with plants at the nesting site during breeding or even year round for nesting and roosting. These interactions are not always reciprocally beneficial, but with costs and benefits that change in spatio-temporal contexts, especially in resource-constrained arid zone environments. The overall impacts of bird nesting, especially colonial species, on the growth and reproduction of host trees can be large, with these interactions potentially being crucial components of ecosystems. Overall, understanding the nature of the interactions between host trees and nesting birds may provide key information on understanding the life history of species and their communities. I, therefore, test the hypothesis that the interactions between animals and plants in the savanna ecosystem enhance the islands of fertility created by trees, which influences the growth and survival of vegetation in the environment. I used the interaction between sociable weavers (Philetairus socius) and their host trees (camelthorn Vachellia erioloba and shepherd Boscia albitrunca) to test this hypothesis. I predicted that trees that host the sociable weaver nest would have benefits and costs in the interaction, influencing the growth and reproduction of host trees differently from trees without a nest. I found that soils under trees without nests were characterized by higher N (2.3-fold) and P (1.3-fold) compared to grassland areas. However, I found that soils under nest trees had even higher concentrations of N (3.5-fold) and P (4.1-fold) than soils under trees without nests. Therefore, nest trees and trees without nests create islands of fertility, but nests accentuate nutrient accumulation. Soil C and N increased with increasing tree size and colony size. Seedling growth was significantly greater in the soils from islands of fertility that were accentuated by weaver nest presence. Seedlings grown in soils from bird islands of fertility showed more growth in shoots, while seedlings in grasslands showed more growth in roots, and lastly, tree islands of fertility were intermediate in both. There was significantly greater mean seedling height (1.4-fold) and the number of leaves (1.4-fold) in soils from bird islands of fertility than in both tree islands of fertility and grassland sites. The foliar nutrient stoichiometries of seedlings grown on nest-accentuated islands of fertility were similar to the stoichiometric ratios in soils from bird islands of fertility, showing that the faecal input of the sociable weaver accounts for the growth differences in these islands of fertility. The benefits for trees that host sociable weaver nests include higher foliar N, P, K, and Ca. Trees hosting nests did not show differences in seed weight, number of seeds per pod and pod weight. Seed nutrients did not vary substantially between trees with and without a nest. Seed germination and emergence did not differ between trees with and without a nest. There was, however, significantly shorter seed germination and emergence time in seeds infested with beetles than in seeds with no beetle infestation. The costs of hosting a sociable weaver nest include lower soil water infiltration rates under nest trees with larger colony sizes, which limits seed germination, despite good seed banks and nutrient-rich soils. There was also an average of 30% reduction in the photosynthetic area of nest trees, significantly more and larger branch fall in nest trees, and a mean of 39% dead terminal nest branches. The rate of dieback in trees was higher (ca. 6-fold) for nest trees than for trees without a nest. Trees with nests have significantly greater damage from beetles to the seeds (50% infestation) than trees without nests (34% infestation). Beetle-infested seeds in nest trees had a significantly high percentage of seeds that failed to emerge after germination than beetle-infested seeds in control trees. The ecological engineering activities of sociable weavers address the limitations of nutrients for the growth of the host tree in an arid zone savanna, but there is also a growth and reproductive cost for the host trees. The biotic interaction between sociable weavers and their host trees facilitates the survival of host trees in the resource-constrained arid zone savanna environment. In this interaction, there are growth costs to hosting the nest, but there were no substantial reproductive costs to host trees except for a high beetle infestation of host seeds. These combinations of feedback also establish the camelthorn and shepherd trees as powerful ecosystem engineers. The study also contributes to the literature on ecological engineering, showing how the association between the sociable weavers and savanna trees ameliorate conditions in N-limited desert soils which drives the growth of plants in this soil condition.
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    The influence of vulture restaurants on breeding success and nestling body condition of Gyps vulture populations across southern Africa
    (2018) Zimunya, Tapiwa; Thomson, Robert; Amar, Arjun
    Vulture populations in many parts of the world continue to decline owing to numerous threats, such as lack of adequate food sources, poisoning and collisions with power-lines. Worldwide, supplementary feeding sites (hereafter, vulture restaurants) have been used as a conservation tool aimed at supporting vulture populations. However, in many parts of the world there is little scientific evidence about their effectiveness in aiding vulture populations. Here, I assessed the relationship between chick condition (African White-backed Vultures) and breeding success (Cape Vultures/African White-backed Vultures) in relation to a variety of variables which described levels of access to vulture restaurants. My data suggest the potential of vulture restaurants to increase breeding success in vulture populations. Breeding success generally increased for nests closer to vulture restaurants. There was a significant positive correlation between African White-backed Vulture breeding success and proximity to vulture restaurants (p< 0.05), but little evidence to support such a relationship for Cape Vultures (p> 0.05). Nestling body condition of African White-backed Vultures was also not influenced by proximity to vulture restaurants (p> 0.05). Findings of this study provide motivation on the use of vulture restaurants as a conservation strategy across southern Africa. The current study informs future conservation efforts on the use of vulture restaurants across the region, particularly in countries where a network of vulture restaurants is still being established.
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    The role of supplementary feeding sites in vulture conservation in South Africa
    (2022) Brink, Christiaan Willem; Thomson, Robert; Santangeli, Andrea; Amar, Arjun
    Supplementary feeding is a management application often used to support declining wildlife populations or facilitate reintroductions. Nowhere is it perhaps more popular, than in vulture conservation. Vulture supplementary feeding sites (SFS), also known as vulture restaurants, are specific locations where carcasses and unwanted animal parts are provided for vultures to feed on. This is proposed to be a win-win scenario in that contributors to the site receive a free carcass disposal service while simultaneously supporting vulture populations. SFS are assumed to benefit vultures through enhancing demographic parameters such as breeding success and survival. While there is some evidence for such effects, more recent critical assessments are questioning assumptions that these effects are ubiquitous. Additionally, research has begun to identify unintended negative consequences to both target and non-target species and the larger ecosystem. SFS may consequently be counterproductive to conservation goals in some cases. Most of these critical assessments have been conducted in Europe, and southern Africa, the supposed birthplace of SFS, remains understudied. In light of the ongoing African vulture crisis, which has seen vulture populations plummet across the continent, effective investment of conservation resources is critical in preventing the extinction of this functional group. The main aim of this thesis was therefore to evaluate what role SFS play in vulture conservation in a southern African context. I specifically focus on South Africa, where SFS is widespread and have a long history. To understand the value of SFS I needed to verify the proposed positive effects of this conservation measure and assess any potential negative consequences of the practice. First, this required base-line information on the scale and extent of the practice. Secondly management practices and the motivations of managers needed to be reviewed to understand the context in which these sites function and whether there are any risks to vultures using these sites. Thirdly, the distribution of the major threat to vultures (i.e., poisoned carcasses), which SFS are proposed to mitigate, needed to be determined. And finally, the presumed positive effect of SFS on vultures needed to be tested. I could then examine the potential trade-offs of this management practice. In this thesis I first describe the distribution and contribution of SFS to vultures at a national level. I do this by compiling records and databases from various organisations involved in vulture conservation. Then, using a snow-ball survey method and telephonic and email interviews, I verify the activity and history of all recorded and newly discovered SFS. Using this method, I identify 143 currently active SFS across the country, feeding an average of 64.6 kg per day. Overall provisioning at SFS amounted to an estimated 3301 tonnes of food per year. An amount equivalent to 83% of the food requirements of all vultures in the region. I show that different vulture species have varying access to this resource depending on their range. Food provisioning was highly skewed to only 17% of SFS which are providing 69% of the food. Consequently, species with smaller home ranges have relatively poor access to food provided at SFS when compared to further ranging species. In this first chapter, I provide the necessary base-line information that has previously hampered the critical assessment of the effects of this intervention. Using information from the survey conducted with SFS managers I then investigate the context in which these SFS function and their adherence to best management practices. Half of the SFS surveyed were associated with livestock farming and the majority were private individuals not officially affiliated with any conservation organisation. The pervasive sentiment under managers is that SFS are beneficial (84% of managers) and most managers are unable to indicate any disadvantages to themselves in the running of SFS. The cleaning service provided by the vultures is the most widespread perceived benefit. While managers may receive benefits from this practice, I show that their low awareness of vulture conservation issues may lead to practices that are harmful to vultures. For example, despite experts identifying unintentional and intentional poisoning from poison laced carcasses as the most critical threats to vultures, only 47 and 24% of managers, respectively, listed these as potential threats to vultures. Additionally, while most managers (85%) assess carcasses for provisioning suitability based on whether they had been treated with veterinary drugs, relatively few managers (10%) did the same for lead (Pb) contamination. Worryingly, only 30% of managers consider threats to vultures, such as the proximity of power lines, when deciding on a location for their SFS. Overall, current management practices are not adequate to guarantee the safety of vultures using SFS. I therefore advise that increased awareness and training is required and perhaps more stringent guidelines and regulation of the practice. As I show a correlation between the numbers of vultures seen at SFS and the amount of food provided there, the initial focus for such training and regulation should be the SFS with the highest provisioning rates. More formal regulation of this practices will also allow for its targeted application in relation to threats in the landscape. To inform such management and to control for the major cause of vulture declines in subsequent analysis, I investigate the prevalence and motivations for using poison as a predator control method under livestock farmers. I do this via face-to-face surveys using a specialised questioning technique and ad hoc quantitative methods. This reveals that an estimated 22% and 31% of farmers use poison over a 1-year and 5-year period, respectively. Poison use hotspots generally coincide with small stock farming areas and the strongest predictor for its use is its perceived prevalence under peers. My results, however, indicate that farmers are less likely to use poisons if they frequently encounter vultures on their farm. The widespread positive attitude displayed towards vultures along with the other findings provide leverage points to change behaviours and mitigate this threat. In addition to the proposition that SFS mitigate the threat from poison laced carcasses, they are also proposed to assist breeding vultures and increase their success in raising young. To test this, I use monitoring data on South African Cape vulture colonies spanning over two decades, to model the effects of SFS on breeding success, while accounting for threats such as poison use and the provisioning of Pb contaminated food. I also test whether Pb contaminated food potentially proved at SFS is affecting breeding success. I show that the amount of food provided annually at SFS is weakly positively associated with breeding success, but that these results are not significant. I find that a reduced proximity of SFS to vulture colonies is negatively associated with breeding success, but this result is also not significant. Lastly, I find no evidence that the amount of potentially Pb contaminated food provided at SFS, nor the average prevalence of carcass poisoning in the area, affected local breeding success. These results cast doubt on the current dominant narrative in the conservation sphere, which asserts that SFS have positive effects on vulture demographic parameters, such as breeding success. In this thesis, I show that some a priori assumptions about the benefits of SFS in vulture conservation may be overvalued and unjustified. Furthermore, I uncover that current management practices may be endangering vultures feeding at these sites, the problem of which is heightened by the identified widespread use and level of provisioning occurring at a landscape scale. It is therefore an urgent matter to examine other effects, both positive and negative, that SFS have on vultures and the rest of the ecosystem. In this thesis I have provided the necessary information to conduct such research. Until a net benefit to vultures is shown a refocussing of conservation efforts on directly combatting the major causes of vulture declines may be warranted to ensure the effective spending of limited conservation resources.
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    Understanding predation of tortoises by nesting Pied Crows (Corvus albus) in western South Africa
    (2017) Durà i Franch, Carles; Amar, Arjun; Thomson, Robert
    Many species in a wide variety of taxonomic groups have shown shifts in their distribution ranges in recent decades. Rapidly changing distributions may lead to novel biotic interactions between species that have not historically interacted. As generalist predators, corvids are a potential threat to other species in areas where they have recently colonized or where their numbers have increased. Tortoise species appear to be one taxonomic group that may potentially suffer serious negative effects from increased corvid abundance. One species of corvid which has shown a significant range increase in the last two decades in western South Africa is the Pied Crow (Corvus albus). In conjunction with this expansion have come observed accounts of large numbers of tortoises being found depredated under Pied Crow nests, raising concerns over their impact on tortoises in these areas. Southern Africa has the richest biodiversity of tortoises in the world and a high rate of endemism. The endemic species are mainly restricted to the Cape region, where the genera Chersina, Homopus and Psammobates have their evolutionary centre. In this thesis, I explore how widespread tortoise predation by Pied Crows was during the crow's breeding season. I aimed to quantify the proportion of Pied Crow pairs that provision tortoise to their chicks and the numbers being depredated, as well as the species of tortoises involved. During the 2016 breeding season, I monitored 125 active Pied Crow nests in western South Africa. For the majority of these nests (n=93) there was no evidence for any tortoise predation. For the 32 pairs, where predation was recorded, I found that 15 pairs depredated ≤1 tortoise – week, five pairs depredated depredated between 1 and 2 tortoise–week , and 12 pairs depredated >2 tortoises–week. The tortoises prey remains found depredated depredated under Pied Crow nests had an average straight carapace length of 5.57 cm (range 3.5 cm - 9.8 cm) and 91% of them were Angulate Tortoises. Crows favour smaller tortoises with impacts for smaller species, or younger age classes. I also explored whether any environmental variables explained probability of tortoise predation or predation rates. Environmental variables examined included weather variables, land cover types, distances to roads and primary productivity values, and for a subset of nests the abundance of tortoises counted from transects. Although predation rate showed spatial variation among the study areas with most predation occurring in arid areas with high mean temperatures and low rainfall, no single environmental variable successfully predicted the variation in spatial predation.
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    Using Conditioned Food Aversion (CFA) to reduce Pied Crow (Corbus albus) predation of plover nests
    (2016) Ferguson, Angela; Flower, Thomas; Thomson, Robert
    Nest predation is one of the principle constraints on bird breeding success, accounting for 20 to 80% of all nest failures. It can be exacerbated by anthropogenic factors and the resultant increased predation pressure has caused the decline of numerous bird species worldwide. Identifying management strategies to reduce nest predation is consequently a priority for biodiversity conservation. Many lethal and non-lethal methods of predator control can be ineffective, unethical, time-consuming and expensive to implement. An alternative is the use of Conditioned Food Aversion (CFA), a method by which animals are deliberately induced to avoid nests following consumption of eggs treated with an illness-inducing toxin. Previous studies suggest that this technique is effective but many have been subject to several methodological flaws that limit their applicability. Here I employ an improved experimental design that uses both spatial and temporal controls and incorporates quantification of predator identity and abundance. By so doing the resultant effects can be attributed to CFA treatment with higher certainty. In the Berg River Estuary, South Africa, nest losses of the Kittlitz's Plover (Charadrius pecuarius) are high due to Pied Crow (Corvus albus) nest predation. I used this common plover as a model species to test whether CFA can be used as a conservation management tool to reduce nest predation. I used a field experiment to assess whether provisioning quail eggs treated with carbachol, an illness-inducing chemical, resulted in reduced nest predation. To assess the effects of treatment, nest survival data for both artificial plover nests containing quail eggs and natural Kittlitz's plover nests, as well as predator abundance were compared across three experimental phases (pre-treatment, treatment and post-treatment) and according to treatment type (carbachol versus water).