Browsing by Author "Amar, Arjun"

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    A mechanistic approach to understanding the colour polymorphism in black sparrowhawks (Accipiter melanoleucus)
    (2021) Nebel, Carina; Amar, Arjun; Sumasgutner, Petra
    Species that exhibit large variation in phenotypic traits, are commonly considered to have a stronger evolutionary potential. However, how they are capable to maintain polymorphisms remains a fundamental problem in evolutionary biology. Colour polymorphic species provide ideal study systems to explore the processes that lead to variation maintenance. About 3.5% of all bird species are colour polymorphic, but it is an especially common phenomenon in Accipitridae (22%), which indicates that it has an adaptive function in this bird group and makes them ideal model systems to study evolutionary processes. The black sparrowhawk (Accipiter melanoleucus) occurs in two discrete colour variants: dark and light. The two morphs differ in the expression of white and black feathers on the breast, belly and underwing coverts. The morph has been associated with ambient light-dependent foraging success and activity behaviour: Dark morphs forage more and have higher foraging success under low light conditions whereas light morphs forage independently of light levels but are better foragers under bright light conditions. This is hypothesized to be due to a crypsis advantage for the morphs under these conditions. During the winter breeding period, the predominating low light conditions on the Cape Peninsula (Western Cape, South Africa) could create an advantage for dark morphs, which should result in their higher survival and higher breeding success. However, this is not the case and only when the two morphs come together to breed, there is a fitness difference: mixed-morph pairs (that consist of a dark and a light morph) have higher breeding success than like-morph pairs (that consist of the same morph) and offspring of mixed-morphs have higher survival rates. This higher success of mixed-morph pairs is hypothesized to be due to emergent pair-level properties with the two morphs being able to expand the hunting niche as a pair. This ‘complementarity hypothesis' is based on previous research conducted on the study system. The aim of this PhD was to explore the mechanistic background of colour polymorphism maintenance in the black sparrowhawk. (i) I performed an experiment in which I test whether there is a morph- and ambient light-dependent crypsis advantage in the black sparrowhawk. I measure the reaction time of feral pigeons towards a simulated hawk attack but did not find indication of such an effect as pigeons reacted the same towards the two morphs. In line with the complementarity hypothesis, (ii) I found that mixed-morph parents provide food more consistently to the nest than like-morph parents. This results in a more predictable food supply for nestlings and buffers against long periods of malnourishment. However, (iii) I was unable to determine the mechanistic link between food supply and higher survival: nestlings of mixedand like-morph pairs had the same levels of innate immune function. Thus, an improved innate immune function in nestlings of mixed-morph pairs is unlikely associated with their higher survival rates. (iv) I performed individual-based model simulations which incorporate multiple key fitness parameters and found that complementarity – in combination with morphdependent seasonality-associated fitness effects – explains the stable colour morph equilibrium in this population. I conclude that emergent pair-level properties which arise due to the complementary nature of the two morphs play an important role in maintaining polymorphism in this species. Complementarity might not only be restricted to colour polymorphic species but could be present in other polymorphic traits that allow parents to behaviourally complement each other when raising their young.
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    Changes in nesting numbers and breeding success of African White-backed Vultures in northern Botswana
    (2018) Leepile, Leungo Boikanyo L; Amar, Arjun; Maude, Glyn
    African White-backed Vultures have recently been uplisted to Critically Endangered by the IUCN due to declines across their range mainly linked to high levels of poisoning. Botswana likely supports significant numbers of this species, but as yet there is no published information on their population trends or their breeding success in this country. However, in recent years within Botswana and neighbouring countries there have been multiple incidents of mass poisonings, which have resulted in the deaths of thousands of White-backed Vultures. I therefore expected that nesting numbers of this species may have declined in this region, with potential additional negative impacts to breeding success. I used information from aerial surveys conducted between 2006 and 2017 in Khwai and Linyanti, two of the most important breeding areas for this species in northern Botswana to examine changes in nesting numbers and breeding success. The results showed a 53.5% decline in nesting numbers from these colonies, from 99 pairs in 2007 to 46 in 2017; with a greater decline in Linyanti than in Khwai. In both areas breeding success was significantly lower in 2017 than it was ten years ago. Current breeding success rates were generally lower than for other populations in South Africa. A population viability analysis suggested that if the productivity levels detected in 2017 were a true indication of current levels of productivity for this population, and if recent poisoning rates continue, this population has a high probability of extinction in the next 5 to 13 years.
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    Conservation of raptors and vultures in Botswana: with a focus on lappet-faced vultures Torgos tracheliotos
    (2018) Garbett, Rebecca Ann; Amar, Arjun
    Many raptor species are in steep decline across Africa. Botswana is regionally important for many of these species, including vultures, yet information on most raptors in this area is lacking. Along with the rest of the region, Botswana has seen a rise in poisoning incidences which have decimated vulture populations and threaten other scavenging raptor species. As a result, seven out of the nine sub-Saharan species of vulture are now at risk of extinction. The lappet-faced vulture Torgos tracheliotus exists at very low densities in comparison with other African vultures and in 2015 was up-listed to “Endangered” by the IUCN because of its recent rapid decline. Although it is one of the most commonly seen vultures in Botswana and is widespread across the continent, very little is currently known about its ecology. This thesis aims to provide information on how raptors and particularly vultures are faring in Botswana, the possible threats that they face in this region and how we can use ecological information to alleviate these threats by better protecting these species. I repeated transect surveys of raptors in northern Botswana that were first conducted 20 years ago to investigate changes in abundance of raptor species that were included in the original surveys. I used data for 29 raptor species to compare abundance between the two surveys and found that 14 species (48%) had experienced significant declines of between 37% and 97%, and that overall, 18 species had declined by >50%; three of which were vulture species. When I compared the overall trend between the two surveys, I found a 40% decline in total abundance of all raptors. Only three species (all eagles) showed significant increases in abundance, but these were small (6-15%). I then went on to explore changes in abundance inside and outside of protected areas. In contrast to what was anticipated, I found that only two species showed significantly different trends (both eagles). These trends differed, with one species showing larger declines outside of protected areas than inside of them, and the other species increasing outside of protected areas but remaining stable inside of them. The findings suggest that Botswana raptor populations are declining in-line with global raptor populations and that vultures may be equally at risk in Botswana as in other parts of Africa. Protected areas do not appear to act as a buffer for declines for most raptor species, which suggests that drivers of decline are acting in equal measure inside and outside of protected areas. Furthermore, that drivers of decline are indiscriminate of individual species life history and ecological traits, due to declines occurring across a spectrum of species groups. Elevated lead (Pb) levels caused by the ingestion of spent hunting ammunition are of considerable concern to many species of scavenging birds around the world. The importance of Pb for scavenging raptors in Africa however remains under investigated. I therefore explored the association between blood Pb levels (BLLs) of the critically endangered African white-backed vulture Gyps africanus and hunting activity in Botswana. From 566 individuals tested, around 33% had elevated BLLs above those associated with background exposure. Higher BLLs were associated with samples taken inside of the hunting season and from within hunting areas. Additionally, there was a significant interaction between hunting season and areas, with Pb levels declining more steeply between hunting and non-hunting seasons within hunting areas rather than outside of them. Thus, the results are consistent with the suggestion that elevated BLLs in African white-backed vultures are associated with recreational hunting. Pb is known to be highly toxic to scavenging birds and so it is recommended that Pb ammunition in Botswana is phased out as soon as possible to help protect this rapidly declining group of birds. However, a regional ban would be necessary in order to protect vultures from Pb from hunting across their entire range. GPS tracking data from 14 adult lappet-faced vultures Torgos tracheliotos tracked in Botswana from 2012 to 2017 were used to investigate movement ecology. The GPS tags provided information on overall population home range estimates, as well as on home ranges of breeding and non-breeding birds within different breeding seasons. All vultures ranged widely across the region, regularly crossing international borders. The largest minimum convex polygon (100% MCP) range for an individual bird was almost 700 000 km2 . Within the breeding season, 95% and 50% kernel home range estimates (KDE) were significantly different for breeding and non-breeding birds, with home ranges of breeding birds being up to ten times smaller than those of non-breeding birds. Outside of the breeding season, these differences remained but were less striking. Despite large differences in ranging behaviour, use of protected areas (e.g. amount of GPS fixes within protected areas) by breeders and nonbreeders did not differ, either during the breeding season or in the subsequent non-breeding season. However, actual selection of protected and non-protected areas (e.g. use of protected areas according to their availability) did differ for both breeders and non-breeders. This study suggests that conservation strategies need to be different in order to protect different sectors of a population (which I termed ‘full-spectrum’ protection) over different seasons (e.g. ‘fullcycle’ protection). For wide-ranging species, targeted conservation may be the only way to ensure population survival whilst working within practical conservation constraints. The study of breeding and non-breeding populations will assist in designing successful conservation approaches for many species in decline, particularly those that range widely. Because vultures range over vast areas, they are difficult to protect. Using the lappet-faced vulture GPS data, I explored whether Vulture Safe Zones (VSZs) could be useful for vulture conservation in Africa. VSZs are currently being used in Asia to assist the recovery of three Gyps vulture populations that were driven to near extinction due to veterinary drug – diclofenac, in carrion. To explore whether VSZs would work for African vultures I identified areas of highest use by counting GPS fixes of each individual within each 1-degree gridsquare (DGS) within Botswana (total of 59 DGSs), and then using the mean % of use for each DGS to identify the five top scoring DGSs which would form the VSZ (an area of c. 50,000 km2 ). This was performed for three different groups within the population: 1) all individuals, 2) active breeders and 3) non-breeders. On evaluating the differences between the protection of GPS fixes offered by VSZs for each bird group, the best protection was offered by VSZs targeting breeding birds, at around 80% cumulative protection of their total movements in Botswana, as well as a high level of individual protection. VSZs aimed at protecting non-breeders and all individuals, protected 35% less of their movements in Botswana than VSZs for breeders, as well as offering much less individual protection. Thus, VSZs aimed at protecting breeding birds were most effective and could be a viable conservation tool for adult lappet-faced vultures (or similarly wide-ranging) species in Africa. Further investigations using larger sample sizes should be used within the framework provided in this study to evaluate the potential efficacy of VSZs for protecting African vultures. The findings of this study show that raptors in Botswana are in dire need of conservation attention, but that conservation strategies need to be carefully considered and aimed at achieving ‘full-cycle’ and ‘full-spectrum’ protection of populations. To achieve for African vultures and other wide-ranging species, this will likely require approaches most similar to those suggested for migratory species. Additionally, a move towards protecting ‘greater ecosystems’ e.g. managing wider landscapes outside of protected areas is most likely to be a more realistic step toward protecting wide ranging species and declining global biodiversity in the face of rapidly increasing human pressures across the continent.
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    Differential haemoparasite intensity between black sparrowhawk (Accipiter melanoleucus) morphs suggests an adaptive function for polymorphism
    (Public Library of Science, 2013) Lei, Bonnie; Amar, Arjun; Koeslag, Ann; Gous, Tertius A; Tate, Gareth J
    Recent research suggests that genes coding for melanin based colouration may have pleiotropic properties, in particular conveying raised immune function. Thus adaptive function of polymorphism may be associated with parasite resistance. The black sparrowhawk Accipiter melanoleucus is a polymorphic raptor with two morphs. Over most of its range the light morph is commonest, however within the recently colonised Western Cape of South Africa the dark morph predominates. The species breeds in winter throughout South Africa, however unlike in the rest of the species' South African range, the Western Cape experiences a winter rainfall regime, where arthropod vectors which transmit haematozoan parasites may be more abundant. We hypothesise that the higher frequency of dark morph birds in this region may be due to their improved parasite resistance, which enables them to cope with higher parasite pressure. If so, we predict that dark morph black sparrowhawks would have lower parasite burdens than light morph birds. Within our population the prevalence of the two most common haematozoan parasites was high, with 72% of adults infected with Haemoproteus nisi and 59% of adults infected with Leucocytozoon toddi . We found no difference in prevalence for either parasite between adult morphs, or between chicks of different parental morphs. However, within adults infected with H. nisi , infection intensity was significantly higher in light morphs than dark morphs. This suggests that dark morphs have lower parasite loads than light morphs due to resistance rather than morph-specific habitat exploitation. Greater resistance to Haemoproteus parasites may therefore be one of the mechanisms through which dark morph black sparrowhawks have a selective advantage in this region and may explain why they are most common in our study area. In other regions, the cost to benefit ratio may be in favour of the light morph, where parasites are less abundant or virulent.
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    Differential range use between age classes of southern African Bearded Vultures Gypaetus barbatus
    (Public Library of Science, 2014) Krüger, Sonja; Reid, Timothy; Amar, Arjun
    Bearded Vulture Gypaetus barbatus movements were investigated in southern Africa to determine whether an individual's age, sex or breeding status influenced its ranging behaviour and to provide the information required to guide conservation activities. Data from satellite transmitters fitted to 18 individuals of four age classes were used to determine range size and use. Because of the nature of the movements of marked individuals, these data could be used to determine the overall foraging range of the entire population, which was estimated to be 51 767 km 2 . Although juvenile, immature and sub-adult birds used different parts of the overall range, their combined foraging range was 65% (33 636 km 2 ) of the overall range. Average adult home ranges (286 km 2 ) were only around 1% the size of the average foraging ranges of non-adults (10 540 -25 985 km 2 ), with those of breeding adults being even smaller (95 km 2 ). Home ranges of breeding adults did not vary in size between seasons but adults utilized their home range more intensively whilst breeding, moving greater distances during the incubation and chick hatching period. Range size and use increased as non-adults aged. Immatures and sub-adults had larger range sizes during winter, but range use of non-adults did not vary seasonally. Range size and use did not differ between the sexes in any of the age classes. Information on home range size and use enables specific areas within the species' range to be targeted for management planning, education and conservation action.
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    Does the Karoo population of Martial Eagles (Polemaetus bellicosus) have the potential to buffer the species? national decline?
    (2023) Doherty, Jane; Amar, Arjun
    There has been a rapid decline in Martial Eagle (Polemaetus bellicosus) sightings across Sub-Saharan Africa, with the species recently up-listed to Endangered. However, in South Africa in recent decades, a population has become established in the Karoo, a largely treeless and semi-arid biome not considered favoured by the species in the past. This shift was likely to have been facilitated by electricity infrastructure, specifically large pylons, on which they now nest. In this study, we attempted a population viability analysis of this population. Our interest was to explore whether the Karoo population might be a source population and, if so, whether it could help buffer the national population from declines seen elsewhere. We used two longitudinal datasets: three years of detailed breeding data from 47 territories, collected through twice-yearly aerial surveys and quarterly on-the-ground monitoring (representing 137 breeding pair years); and tracking data from 19 birds (representing 27 years' data), from 2019 to 2021. We used these data to estimate breeding parameters and to estimate mortality rates for adults and non-adults. These estimates were then entered into the population simulation software, Vortex, creating four scenarios to take into account uncertainties in both our breeding and mortality estimates. The calculated rates of breeding attempt, breeding success and productivity were 53%, 80% and 42%, respectively. Maximum average annual adult and non-adult mortality rates (which assumed that all tracked eagles that disappeared had died) were 24% and 61%, respectively. The equivalent minimum rates (which assumed tag failures for offline birds that had not been confirmed dead) were 9% and 38%, respectively. Our models suggested that the Karoo sub-population will, at best, shrink by 10% per annum over the next 20 years. At worst, the population will shrink by 30% per annum. At these rates, and without immigration by individuals from other populations, the Karoo population will be close to extinction – if not already extinct – in two decades. Evidently, the Karoo population will not be able to buffer the species' national decline: it could even be a sink for eagles from source populations elsewhere. However, our models are highly sensitive to our survival rates which, because of our small sample size, may be relatively poorly estimated. We suggest that, in order to improve our understanding of the future population dynamics of this species, improved survival estimates should be obtained for the Karoo, as well as information on patterns of recruitment and dispersal by young eagles and adult floaters.
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    Ecology of the Verreaux's eagle Aquila verreauxii in natural and agriculturally transformed habitats in South Africa
    (2016) Murgatroyd, Sarah Megan; Underhill, Leslie G; Amar, Arjun
    Agricultural transformation generally has a negative impact on biodiversity. Owing to landscape fragmentation and reduced prey availability, predators that inhabit transformed areas are usually forced to increase hunting effort or diversify their diet and this can have negative consequences for fitness or demographic parameters. Agricultural landscapes are therefore rarely considered important in the conservation of top predators. The Verreaux's eagle Aquila verreauxii has experienced loss of natural habitat due to agricultural transformation through much of its range. Despite the conspicuous nature and widespread distribution of Verreaux's eagles in sub- Saharan Africa, there is a paucity of information on the mechanism behind the recently observed population declines of this species, which have resulted in the recent re-classification as "Vulnerable" (from "Least Concern") in South Africa. This thesis aims to explore how land transformation influences changes in several key ecological components and demographic parameters, namely breeding performance, diet and movement ecology. In this thesis, I study two geographically adjacent populations of Verreaux's eagles; one located in a natural area (Cederberg) and one in an agriculturally transformed area (Sandveld), in the Western Cape Province, South Africa, from 2011-2014. I investigate the breeding performance of the two populations. In contrast to what was anticipated I found that breeding productivity was 2.7 times greater in the agricultural than in the natural area. Population modelling suggested that in isolation the Cederberg population is unlikely to be self-sustaining, whereas the eagles breeding in the Sandveld region are likely to be acting as a source population. However, I did not have any information about juvenile or adult survival in either area. Contrasting survival rates could distort these results and are in need of further research. Verreaux's eagles are generally regarded as dietary specialists. I therefore investigated the diet composition of eagles in the two study areas as a proxy to better understand prey availability and to look for evidence of behavioural flexibility to different availability of prey resources. The relationship between diet breadth and breeding performance was explored locally and regionally using data from previous studies. Eagles in the Sandveld were found to have a more diverse diet than eagles in the Cederberg, which rely on their traditional prey, rock hyrax Procavia capensis. Theory on specialist predators assumes that diet diversification will cause reduced breeding performance. In particular, individuals within a species with more diverse diets due to reduced availability of primary prey species can display reduced breeding performance. In direct contrast to this, eagles with broad diet did not exhibit trends for reduced breeding performance, both locally and across southern Africa.
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    Environmental factors influencing the breeding and health of a predator endemic to southern Africa: the endangered Black Harrier Circus Maurus
    (2017) García-Heras, Marie-Sophie; Simmons, Robert E; Arroyo, Beatriz; Mougeot, François; Amar, Arjun
    A general and increasing biodiversity loss has been observed since the 20th century. Faced with the extreme rapidity of population declines, conservation biologists seek to understand the limiting and regulating factors driving changes in animal populations. This is particularly important for rare species as small population size increases extinction risk. Birds are amongst the most studied animals in this context. As a group that occupies a high trophic level, raptors are particularly vulnerable to external changes and are generally regarded as useful indicators of ecological change. The Black Harrier Circus maurus is an avian predator endemic to southern Africa, which breeds essentially along the South African coast within the Fynbos biome, and inland within the Karoo biome. Its population size has been estimated at less than 1,000 breeding birds, and the species is currently considered as Endangered in South Africa, Namibia and Lesotho. Although some studies have been conducted on Black Harriers in the last four decades, the reasons for its scarcity currently remain little known and insufficiently explored. Filling this knowledge gap is therefore essential for its conservation. In this context, the main goal of this thesis is to develop an overall comprehension of how various environmental factors may affect the breeding and health of this Endangered species, at both population and individual levels. I conducted my fieldwork during the 2012-2015 breeding seasons in two contrasting geographical regions: one along the west coast in the Western Cape Province, and the second one inland in the surroundings of Nieuwoudtville in the Northern Cape Province. For some chapters (Chapters 1-3), I analysed historical data collected by Dr. R. E. Simmons during 2000-2011 breeding seasons.
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    An experimental assessment of the efficacy of falconry to mitigate human-wildlife conflict: Egyptian Geese Alopochen aegyptiaca at golf courses
    (2015) Atkins, Alexander; Amar, Arjun; Little, Rob
    Human-wildlife conflicts are increasing globally and are believed to be one of the most prevalent and intractable issues that face conservation biologists today. One such conflict is found on golf courses, where high numbers of geese can come into conflict with residents and members. In South Africa, the indigenous Egyptian Goose Alopochen aegyptiaca population has increased dramatically over recent years and as a result they are often seen as nuisance animals whose population requires active management. Most non-lethal methods of goose control have had little success due to habituation to their presence, whilst the use of lethal methods are often deemed socially unacceptable. In this study we experimentally investigated the efficacy of falconry as a management tool to mitigate human-wildlife conflict. We hypothesised that the use of falconry would re-establish a landscape of fear, whereby habitat choice is influenced by the perceived fear of predation, resulting in the local departure of geese to a safer habitat, thereby reducing the population of geese to a tolerable level. Absolute counts of geese and analysis of vigilance levels were conducted at three golf courses in the Western Cape which included two control sites and a treatment site. The results of the experiment indicate that goose abundance declined by 73% at the treatment site after falconry was initiated, and that this was well over the losses due to direct predation. Vigilance levels increased by 7 6% during the treatment period, with no such changes observed at either control site. Additionally, vigilance was higher when filmed from a golf buggy compared to when filmed on foot, which may suggest the geese also learned to associate the golf buggy with the threat of predation, enhancing the overall efficacy of the falconry. While there is a relatively small lethal aspect to falconry, the results of this study confirm that a reduction in the population of geese can be achieved by simulating the naturally occurring non-lethal effects of predation that have been lost in some habitats, as a result of anthropogenic changes to the landscape. To our knowledge, this is the first truly experimental test of the efficacy of falconry to reduce nuisance birds and these important ecological findings have relevance for techniques that people deploy for dealing with human wildlife conflict, particularly where lethal options are unfavourable.
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    Exploring the breeding diet of the Black Sparrowhawk (Accipiter Melanoleucus) on the Cape Peninsula
    (2013) Baigrie, Bruce; Amar, Arjun
    This study investigates the diet of breeding Black Sparrowhawks (Accipiter melanoleucus) on the Cape Peninsula of South Africa. Macro-remains of prey were collected from below and around the vicinity of nests throughout the breeding seasons of 2012 and 2013. These prey items were then identified down to species where possible through the use of a museum reference collection. In both years 85.9% of the individual remains were those of Columbidae, which corresponds with the only other diet study on Black Sparrowhawks. Redeyed Doves were the most common prey species, accounting for around 35% of the diet’s biomass and 45% of the prey items. Helmeted Guineafowl were also an important component of the diet for certain nests, making up on average 26.4% biomass of the diet. I found very little difference in diet between the different stages of breeding (pre-lay, incubation and nestling), despite the fact that females only contribute significantly during the nestling state and are considerably larger than the males. I also found little difference in the diet composition between pairs which bred either earlier or later in the year, despite productivity being significantly higher for earlier breeding pairs. However, a crude analysis of the overall diet per month revealed increased diet breadth in the early lay months as opposed to the later months. This was a result of fluctuations in the presence of Laughing Doves, Feral Pigeons and Helmeted Guineafowl, probably driven by those species breeding behaviour. Lastly, I also found no difference in the diet composition between pairs with either pure or mixed plumage morph compositions in this polymorphic species. This study provides further evidence to the claim that Black Sparrowhawks on the Cape Peninsula are benefiting from man-altered environments that provide perfect habitat for suitable prey.
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    Exploring the maintenance of plumage polymorphism in the Black Sparrowhawk
    (2016) Tate, Gareth John; Amar, Arjun; Bishop, Jacqueline M
    Animals often display striking variation with respect to their phenotype. Intraspecific and interspecific variation in body colour represents one of the most well studied forms of phenotypic variation. For decades evolutionary biologists have been fascinated by the mechanisms that maintain colour variation in species and traditional explanations for this diversity of colour in nature often invoke an interaction between selection for conspicuous signals and natural selection for crypsis. Colour polymorphic species have frequently been used to explore the evolutionary processes that lead to colour variation in species. Geographic variation in colour morph ratios also occurs frequently in polymorphic species and is often considered an ideal model system to examine the interplay of gene flow and local adaptation in populations. This thesis aims to explore the role and maintenance of plumage colour polymorphism in a raptor, the black sparrowhawk. The black sparrowhawk exhibits discrete colour polymorphism, with adults occurring as either white or dark morphs. Within South Africa, the species has undergone a recent range expansion, successfully colonising the Cape Peninsula in the Western Cape. As winter breeders, black sparrowhawks in South Africa now experience two contrasting climatic regimes; dry winters in their historical north-eastern range, and wet winters in the recently colonised Western Cape region. Within this newly colonised region, the dark morph occurs in greatest frequency. Across South Africa, the species displays clinal variation, with the frequency of dark morphs declining from > 75 % in the far south-west on the Cape Peninsula, to < 20 % in the north-east of the country. Two contrasting hypotheses have been proposed for the high frequency of dark morph birds in the Cape Peninsula population; (1) that colour variation is non-adaptive and is simply due to a chance founder effect and strong genetic drift and (2) this is reflective of local adaptation and that irrespective of the founding morph ratios, dark morphs have a selective advantage in this newly colonised environment with its novel winter rainfall regime. The main aims of this study were to determine the (i) ecological and evolutionary mechanisms that influence the maintenance of colour polymorphism in the species and (ii) to establish explanations for the unusually high proportion of dark morphs on the Cape Peninsula. In this thesis I have used a range of ecological and genetic approaches to explore both neutral and adaptationist explanations for the high frequency of dark morphs in my study population. Data from the mitochondrial control region was used to examine the distribution of genetic diversity in several geographic populations of black sparrowhawks across South Africa, allowing the exploration of trait divergence under neutrality. Using a phylogeographic framework, genetic variation was used to (i) quantify the extent to which population structure and gene flow may influence the observed pattern of colour morphs in the focal study population on the Cape Peninsula, and (ii) explore how selection and gene flow may interact to explain the patterns of morph frequencies in my study system. I found very low genetic differentiation between sample sites across South Africa suggesting that substantial gene flow occurs among populations, supporting the hypothesis that selection, and thus local adaptation, is the primary force maintaining colour variation on the Peninsula.
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    Exploring the relationship between restored ecosystem function and species composition: a meta-analysis
    (2013) Forsythe,Katherine Jane; Carrick, Peter; Amar, Arjun
    The idea that biodiversity confers higher levels of ecosystem functioning has been used as an argument for the conservation of biodiversity, and the relationship between these variables has been well researched. Ecosystem restoration often aims to restore former ecosystem functioning as well as specific species assemblages, not just biodiversity. In many cases monitoring programmes lack funds to measure all these aspects and often assume relationships between these variables; however, these relationships remain largely untested. In this thesis, I undertake the first ever meta-analysis of studies measuring ecological function and species composition in restored sites to test whether such a relationship exists. Bray-Curtis similarity measures were used to compare species composition for each site compared to multiple reference sites. Indicators of ecosystem function were also compared to reference sites, taking into account natural variation within reference sites. A weak relationship between ecosystem function and species composition was found, and it differed between different groups of ecosystem functions. Live plant biomass and structural framework ecosystem functions increased in similarity to reference sites as species composition also increased in similarity to reference sites. Nutrients, soil attributes and interactions between biotic component as well as litter and deadwood production, showed little association with species composition, with levels of ecosystem functioning showing little change as species composition became closer to reference sites. Variables relating to nutrients, soil attributes, and biotic interactions were always similar to intact sites regardless of the degree to which species composition had been restored. Live plant biomass, litter and deadwood production, and framework ecosystem functions, however, often did not reach reference levels of functioning, even when full species composition was restored. This analysis found that overall the shape of the relationship indicates redundancy in species composition, suggesting that increasing similarity in terms of species composition initially increases ecosystem function; however beyond a point, additional similarity does not further assist in the restoration of ecosystem function to reference levels of similarity. The main difference to biodiversity ecosystem function relationships comes with the fact that all ecosystem functions were not returned even when restored sites had similar species composition to reference sites, indicating that something, possibly time, is limiting the return of full ecosystem function to restoration sites. Finally, this research indicates that the relationship between species composition and ecosystem function is not consistent and it would be unwise to use species composition or ecosystem function as proxies for one another.
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    Exploring the use of GPS-tracking to investigate the diet of African vultures
    (2023) Mpofu, Charles; Amar, Arjun; Tate, Gareth and Maude, Glyn
    Vultures are highly mobile scavengers that cover vast distances on their daily foraging trips. Vultures display specific spatial and behavioral patterns when feeding on carcasses, and these behaviors are potentially identifiable in the tracks of geographical positioning system (GPS)- tagged birds. Thus, by applying algorithms to classify their movements it may be possible to create a carcass detection system using these spatial signatures. In this study I applied this approach to explore its efficiency in detecting carcasses and describing the diet of 12 GPStagged vultures in Botswana. I tracked five resident vulture species in Botswana using GPStrackers, these were: Cape Vulture (Gyps coprotheres n=2), Hooded Vulture (Necrosyrtes monachus n=2), Lappet faced Vulture (Torgos tracheliotos n=2), African White-backed Vulture (Gyps africanus n=4) and the White-headed Vulture (Trigonoceps occipitalis n=2). I attempted to search as many as possible of the feeding sites identified by the algorithms between January and June 2022. These potential feeding events were ground-truthed to confirm carcass presence. At each investigated site, any carcass found was identified down to species level. The ground-truthed sites constituted 22% (n=109) of all potential feeding sites identified within the study time frame (n=494). Carcasses were recorded at 62% (n=67) of these investigated sites. Carcasses associated with feeding events from all vulture species were located, except for Hooded Vultures. For this species only one site was checked, with no carcass found. At vulture feeding sites, carcasses from a total of ten taxa were identified. These were mainly wild ungulates (84%) with livestock making up a far lower proportion (16%) comprising of cattle (Bos taurus) and donkey (Equus asinus). Elephant (Loxodanta africana) was the most frequently identified taxon in the carcasses (31%; n=21) and was found at feeding sites of all four vulture species. Although sample sizes were relatively small for each species, it appeared that livestock was recorded only at Lappet-faced and White-backed Vulture investigated sites. Furthermore, Cape and White-headed Vultures had wildlife mostly giraffe and elephant at their investigated sites. Potential feeding events were ground-truthed on average 8 ± 8.35 days after the initial identification of the feeding event. The likelihood of detecting a carcass at these sites declined significantly with the amount of time lapsed from initial identification. The intercept of this relationship suggested that at the time of initial identification there was an 85% chance of detecting a carcass. Vegetation biomass at the sites, and the vulture species involved, had no influence on the likelihood of detecting a carcass. My study, on the application of GPS-tracking to understand the diet of a sample of African vultures in Botswana suggests that this technique is a useful approach but requires substantial resources in terms of personnel to investigate the identified feeding events as soon as these events are triggered, to derive a sufficient sample size to characterize the diets of these different vulture species.
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    Factors influencing the timing of breeding in a range expanding raptor at two spatial scales
    (2012) Sebele, Lovelater; Amar, Arjun
    Range shifts and expansions have been recorded in a number of species and it is expected that as climate change proceeds it will result in more species joining this trend. A major concern with these shifts is the suitability of the receiving novel environments, for example, if these areas experience different climatic conditions or prey phenology. One way to evaluate how expanding populations adapt to the environment is through evaluating their breeding patterns. In southern Africa, the Black sparrowhawk (Accipiter melanoleucus) originally existed in Botswana, Mozambique, North Eastern and South Eastern South Africa and Zimbabwe.
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    Fluctuating human activity and associated anthropogenic food availability affect behaviour and parental care of Red-winged Starlings
    (2018) Catto, Sarah; Cunningham, Susan; Amar, Arjun; Sumasgutner, Petra
    Increased food availability associated with urbanisation is widely recognised as one of the key factors influencing avian demography. Temporal fluctuations in food availability, tied to variation in human presence, are of particular interest as they occur frequently in urban environments, but their impacts on the survival and reproduction of birds have not been particularly well-studied. In this study, I explored whether breeding Red-winged Starlings at a university campus in Cape Town, South Africa alter their behaviour and parental care of nestlings in response to fluctuating numbers of people and associated food over a relatively short timescale. I used data from nest watches and behavioural observations collected during both incubation and nestling periods to test whether differences in food availability due to day status (week days with thousands of students present versus weekends with substantially fewer students) affected a number of behaviours related to parental care. I found that, with less available food on weekends, parent birds appeared to trade off feeding their offspring for maintaining their own energetic requirements, meaning that nestlings received less food on weekends. I also found that parents preferentially fed their nestlings natural food on week days, despite an increased availability of anthropogenic food. This suggests that, with increased food availability, birds in this system may use anthropogenic food to supplement their own diets, allowing them to prioritise the feeding of natural food to their chicks. These results provide evidence that fluctuating food resources impact the behaviour and parental care of starlings, but it is still unclear what effect they have on the individual health of adult birds and their developing young. To further enhance our understanding of some of the ecological implications of urbanisation, future research should prioritise understanding the potential health impacts such a variable urban diet may have on the birds exploiting it.
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    Habitat selection of adult bearded vultures Gypaetus barbatus in southern Africa: implications for conservation
    (2021) Sheik Abbass, Mohammad Imthiaz Zulfur Ali; Amar, Arjun; Murgatroyd, Megan; Krüger, Sonja
    The Bearded Vulture, Gypaetus barbatus, was previously distributed across southern and western South Africa, as far south as Cape Town. Today, the entire population in southern Africa is restricted to the Lesotho highlands and the Drakensberg escarpment and nearby mountains in South Africa, where the population continues to decline. Research has shown that territorial abandonment is apparently associated with the density of human settlements within 10km of a territory. This pattern was assumed to be linked to the increased risk of unnatural mortalities in areas with higher human presence. However, habitat use and habitat selection, especially whether the species actively avoids human settlements has not yet been explored and could contribute to this pattern. In this study, we used data from nine adult Bearded Vultures fitted with Global Positioning System (GPS) satellite tags to determine which habitat is being selected. We modelled habitat selection in relation to various topographic and habitat variables, including information on built-up areas (i.e., areas with a high density of buildings). We predicted that birds would select areas of grassland and avoid areas with high building density and adjoining areas. We found that Bearded Vultures selected areas closer to their nest sites and supplementary feeding sites, with steeper slopes, and highly rugged terrain. In terms of habitat, they selected areas with grassland and avoided areas with forest, while cropland was neither selected nor avoided. As predicted Bearded Vultures avoided built-up areas and their vicinity. These results suggest that the Bearded Vulture may be sensitive to the negative impacts of a changing landscape in its distribution range. These results can help conservation managers in guiding development (e.g., human settlement expansion and afforestation) and protecting priority habitats (e.g., grassland) within the breeding range of adult Bearded Vultures.
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    How does urbanisation affect the breeding performance of African Crowned Eagles (Stephanoaetus coronatus)?
    (2019) Muller, Rebecca; Amar, Arjun; Sumasgutner, Petra; McPherson, Shane; Downs, Colleen
    Birds face many challenges from the process of urbanisation. Those species that are able to occupy urban areas offer opportunities to understand processes of acclimatisation to urban life and may help in the development of urban spaces for the benefit of wildlife. In many bird species, individuals that occupy territories in more urban areas show lower productivity and lower body condition of nestlings, which is thought to be mediated by food availability. Most of the studies exploring this issue were done on passerines and carried out in the global north, with very few studies exploring this topic on non-passerines, and even fewer in Africa. Studies addressing urban productivity in apex predators with slow life histories that are often of conservation concern are largely missing. Here, we explore the breeding performance of the African Crowned Eagles (Stephanoaetus coronatus) across an urbanisation gradient in KwaZuluNatal, South Africa. Specifically, we explored the hypothesis that living in an urban environment allows this species, which is typically a biennial breeder, to breed annually more often (i.e. increased breeding rate), and whether this might increase the productivity of this species. We also explore whether there may be any hidden costs of such a breeding strategy by examining the condition of chicks for pairs which had successfully bred in the previous year. We found that Crowned Eagles breeding in more urban areas attempted to breed more often (i.e., higher breeding rate), but that these birds also suffered from lower breeding success. These two contrasting responses counteracted each other and meant that overall productivity (number of young produced per occupied territory) was not influenced by urbanisation. Breeding annually did not appear to have a negative cost on the chick condition, as offspring in the year following a successful breeding attempt did not have lowered body condition. This species appears to be well adjusted to breeding in an urban environment. Crowned Eagles are currently considered vulnerable in South Africa, and ensuring that an urban population of this species is able to persist can help secure the conservation status of this charismatic species.
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    How well do buffer circles capture the ranging behaviours of territorial raptors?
    (2020) Brink, René; Amar, Arjun; Murgatroyd, Megan
    As the world's human population increases, so does the competition for natural resources between humans and wildlife. This competition may be intense for apex predators, such as raptors, which generally require large natural areas in order to maintain their populations. Anthropogenic development within territories can cause individuals to either abandon these sites, reduce their breeding productivity, or cause direct mortality to the territory holding birds. To mitigate such impacts, one method, employed as part of Environmental Impact Assessments (EIA), is the use buffer circles centred on nest sites. Within these buffers the most damaging forms of development are prohibited. This approach assumes that raptors use the space around their nest in a uniform way, but this assumption may not always be correct and few have evaluated the effectiveness of buffer circles at protecting a species' home range. This study uses tracking data to evaluate the effectiveness of buffer circles to cover the ranging movements of six southern African raptor species, throughout the year, as well as during their breeding and non-breeding season. My study revealed that buffer circles whose dimensions were based on the species' 95% Kernel Density Estimate (KDE) did relatively well at capturing the proportion of individual GPS fixes, but did less well at capturing the KDE area from tracked birds. For buffer circles to capture 95% of the home range polygons (95% KDE) they would generally need to be at least twice as large as those that were derived from the 95% KDE home range area, and for some species with very large home ranges (e.g. Lappet-faced Vultures) even buffer circles that were 3 times the size failed to cover 95% of the KDE polygons.
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    The identity, origin and impact of a 'new' buzzard species breeding in South Africa
    (2015) Gwynn, Lisle; Amar, Arjun
    South Africa is traditionally known to play host to two taxa of small Buteo, the endemic and uncommon Forest Buzzard B. trizonatus, and Steppe Buzzard B. b. vulpinus, an abundant Palearctic migrant. Since the late 1970s and early 1980s, a number of buzzards appearing unlike B. trizonatus have been found breeding in the south-west Cape, particularly on the Cape Peninsula and in and around the Elgin Valley, ca.60km east of Cape Town. Some of these buzzards resemble B. b. vulpinus, whilst others appear atypical of both B. trizonatus and B. b. vulpinus. This study conducted genetic and morphological analyses on a number of buzzards sampled in the south-west Cape, and compared them with three candidate taxa considered most likely to, in full or in part, explain the identity of these ‘mystery’ buzzards. The candidate taxa were: Steppe Buzzard B. b. vulpinus, Ménétries’s Buzzard B. b. menetriesi and Forest Buzzard B. trizonatus. Morphology data and genetic samples were collected from 23 buzzards through capture with a Bal-Chatri trap, from chicks in nests, from captive birds brought to rehabilitation centres or from birds found dead. The comparative morphology of the buzzards sampled in the Cape was determined by constructing a Discriminant Component Analysis using 9 morphometric characters which had previously been established as being important in the separation of Old World Buteo taxa (Kruckenhauser et al., 2004). Blood samples were then analysed using 18 polymorphic microsatellite loci designed for Buteo swainsoni (Hull et al., 2007), using the program STRUCTURE 2.3 to analyse the population assignment of the sampled buzzards. The majority of buzzards were found to most closely match B. trizonatus or B. b. vulpinus in their morphology (52%), and their genetic signature (65%). Additionally, two unidentified genetic signatures were evident. One of these signatures remains unresolved, because buzzards with this genetic signature lacked morphological data. The second signature, however, was displayed by buzzards with larger morphology than is known from both B. b. vulpinus and B. trizonatus. Based on previous research these larger buzzards lay most closely within the morphospace of B. b. menetriesi, being far removed from the morphospace of both B. b. vulpinus and B. trizonatus. Thus, it is conceivable that some of the birds belong to this taxon.
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    Investigating the decline of the Martial Eagle (Polemaetus bellicosus) in South Africa
    (2013) Cloete, Daniël; Amar, Arjun
    The Martial Eagle (Polemaetus bellicosus) is an African endemic that occurs over a wide range of habitats but at naturally low densities. There is concern throughout its range that it is declining and it now appears to be strongly reliant on protected areas. It is classified globally as Near Threatened by the IUCN with a current consultation underway to up-list it to Vulnerable or Endangered. In this project I describe and explore the decline of the species across South Africa, using data from two repeated national bird surveys - South African Bird Atlas Projects (SABAP 1: 1987-1993; SABAP 2: 2007-2012). These analyses suggest a relatively uniform decline across South Africa in Martial Eagle reporting rates of 59% over the last 20 years. Alarmingly, these declines also occurred in protected areas, including the traditional strongholds of the Kruger National Park (54% decline) and the Kalahari National Park (44% decline). Independent survey data, undertaken in the Kalahari National Park, confirmed these declines and reinforced the validity of using the two SABAP surveys to examine population change. Within protected areas, the species is still encountered five times more frequently and is six times as abundant as compared to outside protected areas. Between the biomes, the species is encountered the least and has the lowest abundance in the Grassland biome where tree density is low, and has the highest abundance in the Savanna biome where tree density is higher. Examining environmental correlates of these population changes provided some support for two hypotheses on the causes of these declines, with climate change (increases in temperature) and power line densities negatively associated with changes in reporting rates. Although this analysis also suggested support for declines being associated with avian prey declines, this was unlikely to be a major driver nationally, because I found that overall avian prey species actually increased over this time period. Within Kruger National Park changes in reporting rates were negatively associated with Elephant densities, which may be related to a reduction in nesting opportunities (large trees) for the species. These results are an initial attempt to assess the broad drivers of decline and should help focus and prioritize further detailed research to elucidate the mechanisms behind this species decline.