1,721,076 research outputs found
Quantifying national abundance changes of raptors across Botswana using repeat road surveys
Full text linkRaptors are a group of carnivorous birds experiencing considerable population declines across the globe. Despite these declines, many raptor populations remain poorly monitored across most of their ranges and, as with most biodiversity, this is especially true in developing countries, including most countries within Africa. In Botswana, conservationists are growing increasingly concerned about the population trends of many raptor species, especially vultures. Fortuitously, Botswana has over 55,000 km of raptor road transectsurveys originally conducted between 1991-1995. Over two decades later, researchers repeated some of those surveys (c. 21,000 km) in the northern part of Botswana, which revealed declines across multiple raptor species. To complete these re-surveys at a national level, we undertook a repeat of the raptor transect surveys conducted in the southern half of Botswana, covering c. 22,000 km of transects. We then estimated country-wide abundance changes for all species of regularly occurring raptors by combining these two re-surveys. We explored changes for 30 species, 19 (63%) of which exhibited significant changes. Fifteen species (50%) declined significantly, and 4 (13%) species increased significantly, while 11 species (37%) showed nonsignificant declines. Most species displayed similar population trends between the national analysis and the northern re-surveys. Those re-surveys revealed significant declines in 48% of the 29 species examined. The Lappet-faced Vulture (Torgos tracheliotus) showed significant declines of 61% in the northern re-surveys, but in the national analysis, revealed nonsignificant increases of 27%. White-backed Vultures (Gyps africanus) also revealed significant increases of 28% in the national analysis compared to declines shown in the northern resurveys. Whilst our re-surveys suggestsimilarly worrying trends of many raptor species as the northern re-surveys did, we noted increasing population abundance trends for three of the most threatened vulture species. Future research should explore whether certain environmental data (e.g., human modification, climate change, etc.) are associated with the declines of these species, to better understand the drivers for these decline
The Impacts of Corvids on Biodiversity
Full text linkCorvids are often referred to as efficient nest predators with potential negative impacts on biodiversity. Despite the plethora of literature focusing on the impact of corvids on their potential prey, no review has been conducted on the genus Corvus to synthesis these relationships, and to explore their likely impacts on biodiversity. This thesis conducts a systematic literature review on the impacts of corvids on biodiversity by collating information from two study types: experimental studies and correlative studies. The impacts of corvids were diverse and varied between studies, countries and species. The vast majority of studies were on impacts on birds, and of these passerines were the most frequently studied, followed by waders. Collating the results from both experimental and correlative studies revealed a negative impact for 29% (n=50) of cases, whereas no impact was detected in 63% (n=107) of cases, and I found a positive impact (suggesting a beneficial relationship) in 8% (n=13) of cases. Thus, from the studies that have been investigated, the main findings indicate that corvids most frequently have no detectable impact on target species, and that their impacts are certainly not consistently negative. Concerns of corvid impacts have been raised in South Africa, as one indigenous species, the pied crow (Corvus albus) seems to be increasing. The aim was to explore whether changes in pied crow abundance in South Africa correlate with certain covariates which have been suggested to be involved in their increase. These covariates include transmission lines, climate change (temperature and rainfall), and land cover. Using data from the South African Bird Atlas Project (SABAP) in two surveyed periods (SABAP1: 1987-1991; SABAP2: 2007-2012), I examined changes in pied crow reporting rates (a proxy for relative abundance), describing both the overall change between these time periods, and exploring whether these changes were associated with biomes, transmission lines, climate variables, or land cover. A significant overall increase in this proxy for pied crow abundance was found across South Africa in the last 25 years. Increases differed between different habitat types, with increases being greatest in shrublands and urban areas. A full model, including all the potential covariates, found significant relationships between both temperature and rainfall change, with reporting rates. Pied crows are increasing in regions that are becoming hotter and a little wetter, which are predominantly areas in the west and the interior. There were simultaneous decreases of pied crows in the eastern regions of the country. Thus, change appears to be operating at a broad scale associated with large-scale changes in climate (rainfall and temperature). These analyses represent the first attempt to quantify the changes in abundance and range shifts of pied crows in South Africa, and also represent one of the first studies in South Africa empirically to relate bird population changes to medium-term climate change data
Knemidokoptic mite infections on the Cape Peninsula population of Black Sparrowhawks
No full textKnemidokoptes mites (Acari: Knemidokoptidae) are subcutaneous mites that are found in the skin of the face, legs or body of avian hosts, the symptoms of which can range from featherloss and skin lesions to beak deformities. Although known to infect multiple species of Passeriform birds, very few cases have ever been reported in birds of prey. An unusually high number of Black Sparrowhawks of the Cape Peninsula were identified as being affected by these mites, with obvious symptoms such as baldness and leg lesions. This is the first record of a possible epizootic event caused by Knemidokoptic mites in a wild population of a bird of prey. The number of infection cases elsewhere in South Africa was surveyed and it was found that only rare single cases have been reported, meaning that some causal factor is driving the high infection rate in the Cape Peninsula, where a maximum of 5% of the breeding population were recorded as infected in any one year. The subclinical level of this infection was found to be low, with most of the population not having any mites and only a few individuals representing clinical cases. The infections affect on individual fitness was explored and it was found that it had a significant negative effect on breeding success (p<0.05) and productivity (p<0.01), but I was unable to preform a survival analysis, due to lack of data. A male bias in infections was detected, but there was no difference in the probability of infection and the morph of the bird in this polymorphic species. These results therefore suggest that this infection has the potential to affect the stability of this population over time, due to its effect on reproductive success. Although this species is not endangered, this possible epizootic event is of interest to the study of bird-parasite systems, specifically how this study ectoparasite can negatively affect the fitness of their hosts
Does the Karoo population of Martial Eagles (Polemaetus bellicosus) have the potential to buffer the species? national decline?
Full text linkThere 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
Investigating the decline of the Martial Eagle (Polemaetus bellicosus) in South Africa
No full textThe 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
Quantifying bird damage to wine grapes in the Western Cape of South Africa : a questionnaire-based approach
No full textBird-wine grape damage is a globally acknowledged problem that has been the subject of considerable research in many wine growing regions. However, despite the Western Cape of South Africa being a major wine grape growing region, very little research has quantified bird damage in this region and very little is known about the extent of the problem. This research aimed to quantify bird damage to wine grapes in four grape growing regions of the Western Cape, through questionnaires. It also aimed to determine the factors that might explain the patterns of damage observed. 102 questionnaires were sent to the wine farms, and 52 were returned. Of the respondents, 71% reported bird grape damage. The amount of damage per wine farm ranged between 0% and 15% of the total rows of vines across a farm. When exploring the factors associated with whether a wine farm experienced bird damage, it was found that the border habitat of a farm was a significant factor. The composition of the border habitat greatly influenced the probability of bird damage. The PCA showed that tall trees, Fynbos and residential areas specifically increased the probability of bird damage. Within farms that experienced damage, it was found that in different vineyard blocks the areas closer to the edge of a vineyard and to trees were significantly more susceptible to bird damage. The most common reported damage-causing bird species were Red-Winged Starlings (Onycognathus morio) and White-Eyes (Zosterops lateralis). Damage was reported to occur mostly one month before harvest and at harvest time. This research provides a baseline for understanding the nature of bird damage in these regions and will aid future quantitative studies aimed at the management of the problem
The influence of rainfall on the Verreaux's eagle and its prey species in the Matobo hills, Zimbabwe
Full text linkUnderstanding how species respond to variations in weather patterns will be crucial to improve our predictions about how species will cope with climate change. The Verreaux's Eagle (Aquila verreauxii) and its primary prey species the Rock Hyrax (Procavia capensis) and Yellow-spotted Hyrax (Heterohyrax brucei) have been monitored by a long-term citizen science project in the Matobo Hills, Zimbabwe. A previous study associated rainfall patterns with the establishment, breeding density and productivity of Verreaux's Eagles. Fluctuations in hyrax populations have been attributed to fluctuations in rainfall and drought. However, these studies have been limited by the use of total annual rainfall instead of targeted rainfall periods of when biological outcomes are most sensitive to weather phenomena. This study explored critical climate sensitivity windows influencing the Verreaux's Eagle's reading performance and the abundance of its main prey species. We used observations of 109 nests over 37 years (1984-2019) and counts from 20 hyrax den sites for 13 years (1993-2005), together with remotely sensed rainfall data. The probability of attempting to breeding and the probability of producing a fledgling was negatively associated with rainfall. For breeding attempt, the rainfall during June and July, 11-10 months before laying was the most relevant, whereas, for productivity, the rainfall during December to March, nine-five months before fledging was the most relevant. However, the relationship between the rainfall signal and breeding productivity was not significant. Hyrax abundance had a negative quadratic relationship with mean rainfall against their respective climate windows, whereby the abundance of adult and sub-adult hyrax increased with rainfall during July–September but declined thereafter at greater rainfall levels. The abundance of hyrax did not have a significant relationship with the breeding outcomes of the Verreaux's Eagles. This study shows the complexity of the causal relationships between climate and biological outcomes and also the value of long-term data to understanding the impacts of variations in weather patterns to better understand predator-prey dynamics
Factors influencing the timing of breeding in a range expanding raptor at two spatial scales
No full textIncludes abstract.Includes bibliographical references.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
The identity, origin and impact of a 'new' buzzard species breeding in South Africa
No full textSouth 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
Exploring the breeding diet of the Black Sparrowhawk (Accipiter Melanoleucus) on the Cape Peninsula
No full textThis 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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