OpenUCT :: Browsing by Author "Cunningham, Susan"

Browsing by Author "Cunningham, Susan"

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Open Access
Are local range expansions in southerly populations of Aloidendron dichotomum early indicators of a future range shift?
(2019) Grey, Kerry-Anne; Cunningham, Susan; Midgley, Guy; Foden, Wendy
Aloidendron dichotomum is predicted to undergo a south and south-eastern range shift in response to anthropogenic climate warming. Despite this, its range is suggested to be limited by low temperature extremes at the cool range edge and no such range shift has yet been confirmed. However, eco-physiological knowledge necessary to predict and detect this range shift is lacking. This study aimed to determine whether physiological performance of A. dichotomum differs at a regional and local scale, and if so, whether regional and local temperatures explain physiological differences. Performance metrics and temperature data were collected during summer at 14 microsites in two sites at the cool range edge of A. dichotomum. Microsites were stratified by aspect and elevation. This study confirmed that A. dichotomum is performing CAM photosynthesis at its cool range edge. Further, the results provide evidence for the temperature dependence of A. dichotomum’s physiological performance. Higher performance was associated with warmer nights and the warmer north facing slopes. This is in keeping with our hypothesis that A. dichotomum individuals at the cool range edge would take advantage of higher temperatures more typical of their core range areas. Opposing this, higher carbon gain was found at Gannabos - the cooler of the two study sites. This may be due to the less variable rainfall pattern at Gannabos. Furthermore, performance was higher on the flats where temperatures were also cooler. This may be due to lower water runoff on the flats compared to the slopes. As a result, I suggest that the cool range edge of A. dichotomum is limited both by low temperatures and rainfall variability and that, with warming, constraints on these populations are being removed. This is substantiated by the observed high levels of juvenile recruitment in these populations relative to others, and in time, is likely to lead to range expansion in the region.
Open Access
Assessing the climate change vulnerability of reptile and amphibian species found in Table Mountain National Park
(University of Cape Town, 2020) Harper, Jack; Cunningham, Susan; Foden, Wendy; Van Wilgen, Nicola
It is increasingly apparent that climate change and its associated impacts are a major threat to the rich biodiversity of the Cape floristic region. As the knowledge of the associations between biological traits and climate change impacts strengthens it has become clear that the assessment of climate change vulnerability is a key consideration in the management of biodiversity. This study is the first attempt to use a trait-based approach at the scale of a single national park, focusing on the climate change vulnerability of reptile and amphibian species found in Table Mountain National Park (including historically present species). The park and its immediate surrounding areas are home to a rich diversity of herpetofauna including the Critically Endangered Table Mountain ghost frog (Heleophryne rosei), Rose's mountain toadlet (Capensibufo rosei) and micro frog (Microbatrachella capensis), and the Endangered western leopard toad (Sclerophrys pantherina). Amphibian and reptile-specific assessment frameworks of biological and ecological traits were designed to identify the species most sensitive and least able to adapt to climate change pressures. Using a combination of a literature review and expert consultation, 18 species of amphibian and 41 species of reptile were assessed. The assessment highlighted that, in the worst-case scenario, 85% of the park's reptile species and 67% of the park's amphibian species are predicted to be highly vulnerable to climate change. The southern adder (Bitis armata), Cape long-tailed seps (Tetradactylus tetradactylus), Table Mountain ghost frog (Heleophryne rosei) and the Lightfoot's moss frog (Arthroleptella lightfooti) were identified as being the species most vulnerable to climate change within their respective taxa. All three of the Critically Endangered amphibian species were identified as having both high sensitivity and low adaptive capacity to climate change. Among the focal reptile species, climate change vulnerability was independent of current IUCN Red List status, highlighting that species currently not identified to be under threat by other anthropogenic pressures could imminently become threatened by climate change. Spatiallyexplicit presentation of the assessment output will help prioritise the management of areas within Table Mountain National Park that contain a high diversity of climate-vulnerable species. By reducing the threats from other human-associated impacts to these species, and by identifying when direct intervention is appropriate, the park's management can give these species the best opportunity of persistence in an uncertain climate future.
Open Access
Effects of temperature and food availability on the reproductive ecology of an arid-zone bird
(2024) Pattinson, Nicholas B; Cunningham, Susan; McKechnie, Andrew E
For arid-zone birds that breed in spring and summer, the heightened energy, water, and time demands of reproduction and development coincide with the hottest period of the year. For these species, rapid anthropogenic climate warming is exacerbating trade-offs between thermoregulation and self-maintenance or reproduction, posing a severe threat to breeding and population dynamics. There has been a surge in research into the effects of high and increasing environmental temperature on avian ecology. However, the potential for resource availability to moderate environmental temperature effects on birds' behaviour, physiology, morphology, and success during breeding remains understudied. I investigated these lesser-known concepts through monitoring breeding, conducting a supplementary feeding experiment (providing breeding pairs with access to either a high supplementation (high supp.) treatment of ~25g of Zophobas morio or a low supplementation (low supp.) treatment of ~5g of Z. morio every day of the breeding attempt), and analysing long-term data from a population of Southern Yellow-billed Hornbills (Tockus leucomelas; hornbills) in the Kalahari Desert. These hornbills are long-lived and have an unusual breeding strategy whereby the female seals herself inside the nest cavity for the majority of the breeding attempt, leaving the free-ranging male as the sole provisioner to the nest. Hornbills do not drink, with their water inputs comprised entirely of dietary and metabolic water. Therefore, ‘food' equates to ‘resources' (i.e., food and water combined) in this species. I found that supplementary feeding affected the thermoregulation of free-ranging male parents, incarcerated female parents in the nest, and chicks: hornbills in the high supp. treatment showed more gradual increases in body temperature (Tb) and increased hyperthermia avoidance in response to rising nest temperature (Tnest), although high air temperature (Tair) and Tnest still resulted in facultative hyperthermic responses. Some negative effects of high environmental temperatures persisted regardless of resource availability: breeding male hornbills showed Tair-dependent nest provisioning patterns and chicks showed impaired development (i.e., reduced structural growth) and increased stress responses (indicated by increased feather corticosterone [CORT]) at high Tnest irrespective of resource availability. Collectively, these patterns suggested there were some mediating effects of resource availability on hornbill breeding ecology, but that high environmental temperatures nonetheless had negative effects. This study took place during a period of unprecedented climate extremes, from 2018 – 2021. Therefore, it includes detailed data from two very different summer breeding seasons: a hot and dry breeding season (2019/20) and a cool and very wet breeding season which included a 1-in-100-year flooding event (2020/21). During an earlier year of the study (2018/19), drought conditions were so extreme that no hornbills attempted to breed at the study site, therefore no data for this breeding season are included in the thesis. In the cool and wet breeding season, I recorded a) higher provisioning effort by male parents, b) improved hyperthermia avoidance and more gradual increases in Tb in male and female parents and chicks, c) higher post-hatch body mass (Mb), faster tail feather growth, and lower tail feather barb density in breeding females, d) less time in the nest (i.e., fledging sooner), faster Mb gain, and longer tarsi at fledge and faster tail feather growth in chicks, and e) higher breeding success, compared to the hot and dry breeding season. These differences were mostly unexplained by environmental temperature effects, suggesting they were driven by higher resource availability or quality in the cool and wet breeding season. The lack of any effects of the supplementary feeding experiment on variables other than thermoregulation indicated that it could be resource quality, rather than availability, that was the most important resource-related factor affecting the hornbill ecology during this study. However, I did not have resource quality data to test that possibility. An alternative explanation is that the supplementary feeding experiment did not provide enough extra food and water to influence factors other than thermoregulation, or the signal was simply swamped by the unprecedented influx of natural resources associated with incredibly high primary productivity in the flood year. In systems or periods where resources are not limiting one might not expect a significant effect of resource supplementation. Either of these could have undermined my ability to detect potential resource availability effects. Crucially, I found no significant Tnest effects on female parent morphology or on breeding success, in strong contrast to previous findings in this study population, and in the long-term breeding data analysed in this thesis. This was likely a result of significantly reduced Tnest caused by new nest boxes with an insulation layer, compared to previous studies on this population using uninsulated nest boxes. These findings highlight the need for multi-season studies, and the possibility that improved design of nest boxes can positively affect nest microclimate, thereby mitigating severe high Tnest effects. Overall, this thesis attempted to investigate iv whether high environmental temperatures are currently limiting because of a concurrent lack of energy and water aggravating costly trade-offs. If so, then provisioning of supplementary food and water may present viable conservation options for severely affected and conservation dependant species. Moreover, successful breeding in high rainfall years (corresponding to high resource availability) despite high environmental temperatures may facilitate population persistence. Broadly, based on the predominant lack of supplementary feeding effects, results suggested resource availability was not a strong driver of variation in hornbill reproductive ecology. Rather, the results indicated that high environmental temperatures were limiting regardless of resource availability (i.e., for provisioning rate and developing chicks), despite improved hyperthermia avoidance and more gradual increases in Tb at high Tnest. The results also indicated potential effects of resource quality, or that the supplementary feeding experiment was not completely effective, in that the amount of supplementary food may still not have been enough, or may not have met the nutrient or water requirements (i.e., food quality requirements) of the female parents or chicks. The amount of food in the high supp. treatment was designed to be ~100% of the daily requirements of the nest based on previous studies of this population, but the males in the cool and wet season showed that they could considerably increase the amount of food provisioned to the nest compared to what had been recorded before, suggesting that the amount of supplementary food was well-below what could possibly be provisioned. I lacked the data to investigate these possibilities. Results, therefore, leave avenues for future research to investigate, for example, quality versus quantity effects or the effects of ad libitum food and water supplementation. This PhD contributes to disentangling the independent effects of high environmental temperatures and resource availability on arid-zone avian ecology. Several key potential effects of resource availability or quality on behaviour, physiology, morphology, and breeding success were identified, which ultimately will hopefully aid in understanding avian ecology and designing future research and conservation interventions in the face of rapid climate warming.
Open Access
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.
Open Access
Heat tolerance of Southern Pied Babblers in the Kalahari Desert : how will they respond to climate change?
(2011) Du Plessis, Katherine; Hockey, Phil A R; Ridley, Amanda; Martin, Rowan; Cunningham, Susan
An increasing incidence of mass mortalities of birds in hot deserts suggests that birds may be appropriate candidates for assessing how natural selection, under the influence of climate change, drives adaptation. ... The effects of ambient temperature on daily weight gain, foraging effort and efficiency and the presence of heat-dissipation behaviours were assessed to determine the mechanisms by which increased temperature affect babbler body condition.
Open Access
How common ravens (Corvus corax) exploit anthropogenic food sources through time and space in a semi-transformed, alpine environment
(2021) Jain, Varalika; Sumasgutner, Petra; Cunningham, Susan; Bugnyar, Thomas; Loretto, Matthias
From large-scale agriculture and farming to concentrated fishing discards, garbage dumps, game carcasses and bird feeders, human action has been increasingly affecting natural systems and animal species through the deliberate and unintentional provisioning of food resources. Anthropogenic food sources (AFSs) are often more spatially concentrated, easily accessible, abundant and stable than natural food sources. The common raven, Corvus corax, is a behaviourally flexible and ecologically adaptable species that has managed to thrive in human transformed landscapes by exploiting these anthropogenic sources of food. The aim of this research was to investigate how raven individuals vary in their use of different AFSs through space and time. I used data from a long-term GPS tracking initiative in the Upper Austrian Alps to investigate (1) the space-use of non-breeding raven individuals across this landscape to answer the questions: (2) what types of AFSs are most extensively used by ravens in this landscape, and what factors predict individual variation in AFS use (i.e., apparent reliance on and access to resources), specifically (3a) the number of AFSs visited and (3b) the probability of being at AFSs at any given point in time. Movement patterns can reveal information on the foraging decisions made by individuals, including how they use different AFSs. Non-breeding raven individuals exhibited great variation in how they moved around and used the landscape. The number of AFSs visited, but not the probability of being at an AFS (at any given point in time), varied among individuals with different ranging behaviour and of different age class (i.e., juvenile and adults) and origin (i.e., captive-bred-released and wild-caught), suggesting that experience affects AFS-use. Non-breeders differed in their use of AFSs by season, visiting the highest number of AFSs but having the lowest probability being present at an AFS in winter, potentially indicative of high foraging competition under stressful environmental conditions. They were also found to extensively exploit resources in spring, both visiting high numbers of AFSs and having a high probability of being present at an AFS, perhaps due to decreased competition (e.g., from breeders) and increases in food availability. The category (i.e., wildpark, refuse site, hut) of AFSs also influenced the probability of an individual being present at the site, likely because of differences in resource quality, quantity and replenishing rate. A very few foraging sites were highly popular, while over half attracted less than 5 individuals throughout the study. By exploiting AFSs, raven population numbers have increased across their range, raising conservation concerns (i.e., predation on threatened species and human-wildlife conflict). With a better understanding of the patterns of AFS-use and the factors influencing these patterns, I suggest that strategies to manage ravens in this semi-transformed, alpine environment should focus on controlling the supply of food at AFSs at a regional scale.
Open Access
The influence of temperature on parental investiment in Common Fiscal and consequences for nestling growth
(2014) Sadondo, Phenias; Cunningham, Susan; Martin, Rowan; Ryan, Peter G
Global climate models project a 1.5-4oC increase in the Earth’s temperature by 2100. Africa, especially southern Africa, is expected to experience not only an increase in average temperatures but also an increase in the frequency and duration of extreme temperature events. Increasing temperatures will result in increased vulnerability to heat and drought stress to biodiversity. A recent paper by Cunningham et al. (2013) showed that temperature has a negative effect on daily mass gain in the nestlings of Common Fiscal (Lanius collaris) breeding in the southern Kalahari. This effect may be driven by parents modifying their provisioning rates at high temperature, but the mechanisms underpinning the relationship are not known. I investigate the influence of temperature on parental investment in Common Fiscal and the consequences of high temperatures for nestling growth using data from videos that were filmed in the Kalahari, Northern Cape, South Africa. Daily mass gain by nestlings increased with increasing provisioning rate and decreased in relation to the proportion of time chicks spent panting. Prey provisioning decreased with temperature in larger broods, however, there was no evidence to suggest that parents trade off provisioning and nest attendance. This might mean that prey availability is reduced at high temperatures, or that parents prioritise their own thermoregulation over provisioning.
Open Access
Physiological tolerances of high temperatures in Fynbos birds: implications for climate change
(2014) Milne, Robyn; Ryan, Peter G; Cunningham, Susan; Alan, Lee; Smit, Ben
Climate change is a reality. Numerous biological systems have already responded to changes in climate, with range shifts towards higher latitudes and altitudes being one of the most common responses to climate warming. Bioclimatic envelope modelling provides a useful method for predicting a species, future distribution under a given climate change scenario. However, these models require verification with empirical evidence, including physiological information. Endotherm species (such as birds) have a thermal neutral zone (TNZ) which reflects the range of environmental temperatures over which minimal energy is required for thermoregulation. At temperatures above the TNZ, birds expend extra energy to facilitate evaporative water loss in order to maintain a stable body temperature, while some species increase their body temperature to conserve water. The increased costs of thermoregulation at temperatures above the TNZ can impair fitness, which could have implications for population persistence under climate change. The Fynbos biome of South Africa is a biodiversity hotspot and is home to a rich birdlife, including six endemic bird species. Climate change models predict an increase in temperature for this biome, which may alter the ranges of many of these species, resulting in a loss of species richness and diversity. Recent MaxEnt bioclimatic envelope modelling suggests that some Fynbos bird species may be range-restricted by temperature, while others are more likely limited by other bioclimatic variables (e.g. rainfall). These data require physiological verification.
Open Access
The breeding ecology and behavioural adaptations of African black oystercatchers in light of climate change
(2021) Azaki, Bukola Debola Aderewa; Underhill, Leslie; Cunningham, Susan
This thesis examined how weather conditions and other environmental factors influence the vulnerability of nesting African Black Oystercatchers Haematopus moquini (oystercatchers) to climate and habitat change. I explore, for the first time, the behavioural adaptations used by the species to cope with breeding in a limited strip of beach, between high tides and terrestrial predators, and with little nesting shelter, and their breeding decisions to maximise breeding outcomes. Behavioural and breeding data were collected over three breeding seasons (2016—2018) on Robben Island, South Africa (a site with about 5% of the global population of the species) using time-lapse digital cameras and direct observations. Climate and environmental variables were obtained either through on-site iButton data loggers or from the relevant South African meteorological agencies. The results show that oystercatchers are vulnerable to increasing heat loads as temperature increases. However, oystercatchers used a suite of thermoregulatory behaviours to cope with a wide range of environmental temperatures and decreased the length of their incubation bouts as temperature increased. The proximity of the oystercatchers' breeding site to the ocean appears to contribute significantly to their capacity to cope with increasing heat loads. But such sites potentially expose the oystercatchers to the risk of nest losses to storm surges. Oystercatchers reduced this risk by using habitat selection to optimise the placement of their nests close to the midpoint of the beach, but some were constrained by the narrowness of their territories. Oystercatchers also used the biweekly semilunar spring tide cycle to synchronise the incubation start date of their clutches probably to minimise the number of spring tides that they experience during incubation. Predation was the main cause of oystercatcher nest failure. Surprisingly, Mole Snakes Pseudaspis cana were responsible in all cases where the predator identity was known rather than Kelp Gulls which have historically been suggested to be the main agent. Nest predation probability was influenced by temperature and distance to predator-concealing vegetation and increased as more nests became available, causing a seasonal decline of nest survival. Hence, oystercatcher pairs laying large clutches early in the season were more likely to produce one juvenile in a season. The average number of fledgelings per pair per season was 0.38 and close to that (0.35) required to maintain a stable population. These findings improve our understanding of the breeding ecology and behavioural adaptations of the oystercatchers which might help them to cope with climate change as well as provide new insights on which management decisions and further studies can be based.

Browsing by Author "Cunningham, Susan"

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