Browsing by Author "Brown, Mark."

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Altitudinal and seasonal variation in amethyst sunbird physiology.
(2007) Lindsay, Claire Vicky.; Downs, Colleen Thelma.; Brown, Mark.
Southern Africa is characterised by an unpredictable environment with daily and seasonal temperature fluctuations. As a local or non-migratory endothermic species occurring over an altitudinal gradient from the Drakensberg to the coast of KwaZulu- Natal in southern Africa, Amethyst Sunbirds (Chalcomitra amethystina) experience challenging thermal conditions and increased energetic stress as a result of ambient temperature variation. Flexibility of metabolic rates within a species allows for the colonization of different habitats along an altitudinal and thus temperature gradient. It was predicted that over this altitudinal gradient Amethyst Sunbirds would exhibit variation in metabolic rates, particularly basal metabolic rates, pre- and postacclimation, as well as variation in hematocrit levels in winter and summer trials. It was also predicted that Amethyst Sunbirds would exhibit seasonal variation in metabolic parameters. Sunbirds were caught in a winter and summer season (2006-2007) using mist nets in three locations; Underberg (1553 m), Howick (1075 m) and Oribi Gorge (541 m). Upon capture, metabolic rate was measured indirectly by quantifying oxygen consumption (VO2) using flow through respirometry, at 5 and 25°C. Birds were then acclimated at 25°C for 6 weeks on a 12L:12D cycle. VO2 was measured postacclimation at 8 different temperatures (15, 5, 10, 20, 30, 28, 25 and 33°C). Hematocrit levels were taken pre-acclimation and pre-release. Winter and summer data were compared. In the winter trials it was found that there was little variation in VO2 between individuals from the same locality, whereas significant variation was observed at the same temperatures between localities and thus between altitudes. The subpopulation from the highest altitudinal site had the highest basal metabolic rate (BMR). Summer trials showed that metabolic rates did not differ significantly between altitudinal subpopulations of Amethyst Sunbirds, however, BMR was observed to decrease as altitude decreased. The comparison of seasonal data showed that Amethyst Sunbird subpopulations from Underberg and Howick showed higher post-acclimation VO2 values per temperature in winter than in summer trials. Post-acclimation resting metabolic rate (RMR) values for Howick subpopulations were generally higher in winter than in summer, Underberg Amethyst Sunbirds showed a significant difference between summer and winter RMR at 5 and 10°C and Howick sunbirds showed a significant difference in RMR between seasons at 5°C. The Oribi Gorge subpopulation, however, showed no significant differences in metabolic rate between any temperatures when comparing a summer and a winter season. Thermal neutral zones of all of the subpopulations of Amethyst Sunbirds shifted between the winter and summer trial period. This study thus emphasized the need to understand plasticity in metabolic rates and acknowledge altitudinal and seasonal differences within a species, in order to make accurate predictions about a species thermal physiology and responses to changes in ambient temperatures. In particular, the variation in BMR, which is usually used as a species specific value, should be acknowledged in comparative studies of avian metabolic rates or in climate change models.
Aspects of nocturnal physiology and behaviour in malachite sunbirds (Nectarina famosa).
(2007) Wellmann, Andrea Erika.; Downs, Colleen Thelma.; Brown, Mark.
Although sleep forms an important part of an animal’s life, there is a paucity of knowledge about sleep behaviour. The function of sleep in birds is poorly understood, even though birds spend a large part of their lives sleeping. Sleep behaviour in passerine birds has not been looked at as extensively as that of non-passerine birds. I looked at the sleep behaviour of three relatively common passerine birds occurring in southern Africa, namely the Malachite Sunbird (Nectarinia famosa), the Cape White-eye (Zosterops pallidus) and the Fan-tailed Widowbird (Euplectes axillaris). By using an infra-red sensitive camera I described basic sleep behaviours at various ambient temperatures, of all three species, such as sleep position and eye closure, and also investigated the incidence of unihemispheric sleep. Individuals of all three species spent most of the night asleep and kept on waking up intermittently throughout the night, with no significant differences between temperatures. Cape White-eyes and Malachite Sunbirds showed an increase in back sleep and a decrease in front sleep at 5oC. Little evidence of unihemispheric sleep was found, suggesting that it is more likely to occur in non-passerines, especially ground dwelling birds. Diurnal birds generally sleep during the hours of darkness. Most male southern African sunbirds have pectoral tufts, although the function of these is not always understood. In male Malachite Sunbirds it has recently been found that they display their pectoral tufts almost continuously throughout the night, whilst asleep. I explored the possible function of this behaviour and suggest that these tufts might be a deterrent to predators, as they look like ‘eyes’ in the dark. A review of the use and occurrence of pectoral tufts in southern African sunbird species is also presented. Blood glucose concentrations of most birds are much higher than those found in mammals and it is still not known how they evade the complications of such high levels. I investigated the change in blood glucose concentrations of Malachite Sunbirds at two different ambient temperatures and at different times of the night and day and explored the possibility that gluconeogenesis might be used by birds to ‘warm up’ during arousal of torpor in the early morning, before daylight. Generally blood glucose levels were fairly high, between 13.6 and 21.4 mmol/L, which was expected. Blood glucose levels were higher at 5oC than at 25oC and generally lower in the early hours of the morning. Therefore I reject the assumption that Malachite Sunbirds use gluconeogenesis as an additional form of heat generation during torpor. It is thought that the difference in the levels of blood glucose might be a function of the cold temperature and the consumption of their nectarivorous diet. This research clearly highlights the need for further studies to be undertaken in the sleeping behaviours and patterns of birds, especially in southern African species. It also shows that more studies need to be done on the use of pectoral tufts in sunbird species and furthermore it is suggested that more research is needed to elucidate the mechanism by which Malachite Sunbirds are able to rapidly ‘warm up’ during arousal, when in torpor.
Flexibility in metabolic rate in a small Afrotropical bird Zosterops virens.
(2014) Thompson, Lindy Jane.; Downs, Colleen Thelma.; Brown, Mark.
The scientific literature contains hundreds of studies on avian basal metabolic rate (BMR), many of which assumed that BMR was fixed for each species. Yet those from the last few decades have shown avian BMR to be a flexible trait, changing temporarily and reversibly in response to numerous environmental variables. Given that birds from lower latitudes are relatively understudied compared with temperate and Holarctic species, and that seasonal trends in BMR of southern hemisphere birds are not well understood, we looked at seasonal variation in BMR of a small Afrotropical bird, the Cape white-eye (Zosterops virens), over two years, and found that small birds may reverse the direction and amplitude of seasonal change between years. We also looked at circannual rhythm in avian resting metabolism (RMR), and found that peaks and troughs in resting metabolic rate (RMR) may not necessarily correspond with peaks and troughs in ambient temperature, suggesting that some of the confusion regarding the direction and magnitude of seasonal change in avian BMR may be caused by timing of seasonal measurements. Since we were using captive birds for my work, and since captivity may have an effect on avian BMR, we compared the BMR of freshly wild-caught birds with that of long-term captives housed in outdoor aviaries. The captive birds had higher BMR, giving weight to the argument that some physiological data of captive birds should not be used as representative of wild conspecifics, however the direction of seasonal change was similar in freshly wild-caught and long-term captive birds. Along the same vein, acclimation to laboratory conditions, experimental procedure, and different thermal environments, may also affect avian BMR, and thus before we started the final experiment, Cape white-eyes were acclimated to two different thermal regimes, with no change in RMR over an eight-week period, although there was an increase in body mass over the first three weeks, presumably due to the captive diet being of higher quality than a wild one. These results suggested that in some instances, small birds that are freshly wild-caught may not need to be acclimated in terms of their metabolism, before respirometry trials begin. Finally, given that anthropogenic climate change is anticipated to eclipse all other threats to biodiversity, and since many current predictive models pay no heed to metabolic flexibility of birds, we investigated the effect of a 4°C increase in housing temperature on resting metabolism of the Cape white-eye. This temperature increase is equivalent to that predicted for the range of this species by 2080, and therefore gives an indication of the effect of a sustained increase in mean surface air temperature. The results showed only a marginal difference in various metabolic parameters, suggesting that these birds may cope with the mean temperature increase predicted for their range in the coming decades. Together, these results highlight the importance of considering phenotypic flexibility when studying avian resting or basal metabolic rate. This has special implications for seasonal studies that implicitly assume that summer and winter measurements provide snapshots of the maximum and minimum RMR of which birds are capable, and for comparative studies, which may incorporate metabolic data from both wild and captive populations, or from study birds that were acclimated for different periods.
The functional role of birds as pollinators in southern Cape fynbos.
(2018) Whitehead, Kellyn Jean.; Johnson, Steven Dene.; Brown, Mark.
Nectarivorous birds, particularly sunbirds, are important pollinators of plants in the Cape Flora of South Africa, being responsible for pollinating approximately 5% of plant species. However, interactions between plants and nectarivorous birds in the eastern part of the Cape Floristic Region have not received much attention. This study focussed on two putatively bird-pollinated plant species found within the Nature’s Valley area, namely Kniphofia uvaria and Chasmanthe aethiopica. The breeding systems were determined for each species and, due to their patchy population distribution, potential Allee effects on plant fecundity were also tested for. Flowering phenology in the area was also examined to test for associations between flowering of bird-pollinated plant species and the temporal presence of nectarivorous birds. Selective exclusion experiments showed that sunbirds were the main pollinators of K. uvaria and C. aethiopica – fruit set and the number of viable seeds were much higher for untreated (open control) individuals where birds could visit flowers freely, compared to caged individuals which only allowed for insect visitation. Very few seeds developed when plants of the two species were bagged to exclude all pollinators, indicating that the species are not capable of autonomous self-fertilization. Fruit and seed set were determined for patches of K. uvaria and C. aethiopica in order to test for potential Allee effects. There was a significant relation between the percentage of flowers that set fruit and the number of plants per patch for both K. uvaria and C. aethiopica. However, the number of seeds set per flower of K. uvaria and C. aethiopica had no significant relation with the number of plants per patch. Flowering phenology for the area was determined by bi-weekly walks along the two study sites to document plants in flower. Bird presence was determined using data collected from bi-weekly mist netting sessions at the two sites. We then compared the presence of birds with the flowering data of bird-pollinated plant species. For the Kalander Kloof site there were ten bird-pollinated plant species found and eight for the Salt River site. A comparison of the flowering data with bird presence data, indicated that nectar feeding birds were more likely to be present when accessible nectar availability is high. A total of 135 plant species across both sites were documented during the period of this study of which 14 were bird pollinated.
Managing nesting hawksbill turtles (Eretmochelys imbricata) on a small tropical island.
(2018) Gane, Julie Alexandra.; Downs, Colleen Thelma.; Brown, Mark.
Although human impact has caused the hawksbill turtle (Eretmochelys imbricata) to be on the brink of extinction, conservation efforts are on the increase and management strategies are being re-defined to manage the species towards rapid population increases. Numerous conservation measures have been applied and tested, with varying levels of success, to minimize threats and increase hatchling recruitment success rates. Conservation management is imperative for the survival of this species and has been shown to be easiest and most feasible at the nesting and hatching stages. On Cousine Island where this study took place, a turtle monitoring and management program was initiated in 1994 to protect nesting females and incubating eggs at the nesting and hatching stages of the lifecycle. Controversial conservation measures such as the handling of eggs, relocating clutches and application of crab proof barriers, have been applied on an ad hoc basis to minimize the high levels of mortality from natural erosion and crab predation. The merit of these practices, such as the translocation of egg clutches and the implementation of these specific barrier methods has never to our knowledge been scientifically tested using controlled experimentation. The first aim of this study was to find the most effective crab barrier method for increasing hatchling recruitment success and minimising predation rates with limited negative consequences. The second aim was to decipher crab density trends in order to offer a proxy for the number of crabs a nest might be exposed to within an area and develop beach profiles along the entire nesting beach to provide an expression of beach morphology to minimise nest loses from erosion. Finally, we analysed 10 years of nesting ecology and hatching success data with the aim of providing nesting and hatching trends to inform management decisions on Cousine Island into the future. Results across this study indicated that management measures can have both positive and negative effects on the nesting ecology and hatchling recruitment success in particular. We found that hawksbill clutches incubating without crab barriers are susceptible to losing on average a third or more eggs to crab predation than those with a crab barrier in place. Nests which were protected with netting had significantly higher hatchling recruitment success rates and nests protected with fencing had significantly lower predation rates than control nests. The use of netting, however, had a substantial cooling effect which can potentially distort natural sex ratios. Results across the entire study indicated that spatial distribution and environmental variations have an effect on embryonic development, hatchling fitness, sex determination, hatching success and the risk of predation. The hatchling recruitment success on Cousine Island was also found to be affected by nest losses each season from seasonal beach erosion. Beach dynamics were also found to be cyclical and we discovered that the nesting beach is prone to higher levels of erosion than accretion which created significant changes to beach width across the season. This study showed that when focusing turtle conservation measures at the nesting site, hatchling recruitment success can be increased by minimising mortality at the egg and hatchling stage. The aim in the long-term is to assist with the analyses of local and global population dynamics, deciphering threats and minimising the threat of extinction.
Nectar preferences of specialist and occasional avian nectarivores, and their role in the evolution of floral traits.
(2009) Brown, Mark.; Johnson, Steven Dene.; Downs, Colleen Thelma.
Our understanding of bird pollination systems has changed dramatically in the last few years. A long-standing paradigm was that hummingbirds and passerine birds select for different nectar properties in flowers (phylogenetic hypothesis). However, specialist passerines, such as sunbirds, have similar nectar preferences to hummingbirds and nectar in plants pollinated by these two bird groups is strongly convergent. Thus, as an alternative to the existing paradigm, it has been argued that the most useful distinction that can be drawn is that between specialist and generalist avian nectarivores (feeding niche hypothesis). This was supported by phylogenetically-controlled analyses that show that nectar in plants pollinated by specialist avian nectarivores (whether hummingbird or passerine) tends to have a lower volume, higher concentration and higher sucrose content than that in plants pollinated by generalist avian nectarivores. The aim of this thesis was to determine if these trends can be explained by the nectar preferences of avian nectarivores, and to determine whether the generalist-specialist dichotomy can be applied to Kniphofia, a largely bird-pollinated African plant genus. This thesis consists of two sections. In the first, I present data from equicaloric choice experiments to determine sugar preferences of both specialist and occasional nectar feeding birds across a range of concentrations. In addition, I determine apparent sugar assimilation efficiencies and concentration preferences for a range of occasional nectar feeding birds. Using Malachite Sunbirds (Nectarinia famosa), Dark-capped bulbuls (Pycnonotus tricolor), Speckled Mousebirds (Colius striatus) and Red-winged Starlings (Onychognathus morio) (plus Village Weavers (Ploceus cucullatus) in an appendix) as representatives of the major groups of nectar feeding birds in South Africa, I show that some differences occur between occasional nectar feeding birds and all specialist nectar feeding birds studied so far. Specialists show a switch from hexose preference at low (5%) concentrations, exhibit no preference at medium concentrations (10-20%) and prefer sucrose or show no preference at high concentrations (25%). However, specialists are unable to maintain energy balance at low concentrations, and always select the higher concentration when given choices within this range. Occasional nectar feeding birds prefer hexose solutions at low and medium concentrations (5 and 10%), but show varied preferences at higher concentrations. Occasional nectar feeding birds are able to maintain energy balance at low concentrations, and either show no concentration preference, or a preference for lower concentrations when given a choice. Occasional nectar feeding birds show a range in ability to digest sucrose, although some species, like the Dark-capped Bulbul, are quite proficient at it. Surprisingly, no significant difference is found between specialist and occasional nectarivores sugar preferences when analysed globally, even when phyllogeny is accounted for. Instead, I found a significant relationship between body size and bird sugar preference at different concentrations, from which I build the body size hypothesis, which I suggest is a better predictor to use than bird diet type (specialist or occasional nectarivores – feeding niche hypothesis). In the second section of the thesis, I examine the associations between plant traits and nectarivore nectar preferences. This section focuses on flower morphology and nectar characteristics in Kniphofia species, and ecotypes within species, pollinated by specialist versus occasional avian nectarivores. I show that apart from sugar type, which appears to be phylogenetically constrained, flower morphology and nectar characteristics appear to diverge according to whether plants are pollinated by generalist or specialist nectar feeding birds.
Thermoregulation in breeding crowned plovers (Vanellus coronatus)
(2000) Brown, Mark.; Downs, Colleen Thelma.
Ground-nesting birds nesting in the open have to cope with an extreme thermal environment. Their nests egos and chicks are often located within the boundary layer and are exposed to, direct solar radiation. In preventing eggs and chicks from overheating, adult incubating birds expose themselves to severe heat loads. This study looked at two aspects of this system. Firstly, we examined the role of behaviour in the thermoregulation of breeding crowned plovers (Vanellus coronatus). We then examined the development of independent thermoregulation in hatchling crowned plovers. This study assessed the role of shading behaviour in the thermoregulation of incubating crowned plovers (Vanellus coronatus). Shading behaviour was shown to have no direct benefit for eggs, at times even causing eggs to rise close to lethal levels. Instead, shading behaviour played an important role in maintaining incubating bird temperatures at a constant level. We therefore suggest changing the term "shading" to "standing" behaviour. In addition, core body temperatures of free-ranging adult incubating birds and their eggs were examined on both a daily and a seasonal scale. A range of core bird temperature of 8.8° C was measured during the course of the study. Both daily and seasonal differences in core bird temperature occurred. Daily differences are a result of daily circadian rhythms while seasonal differences are explained by changes in ambient temperature. Both daily and seasonal differences in egg temperatures also occurred. The concept of optimum incubation temperature for a species is therefore reconsidered. Differences between and within species may not be as a result of phylogenetic differences as previously reported, but may be as a result of relatively short-term changes in response to ambient temperature changes. The validity of using taxidermic models in thermoregulatory studies was assessed by comparing data collected using both real and model birds. No direct correlations were found between real and model eggs and birds. This suggests that the patterns seen in models may not adequately reflect short term changes that occur in the real system, thus reducing the ability to use such data to make broad generalizations about thermoregulation in general. The models are, however, useful in providing insight into the heat load an animal carries under different environmental conditions, and in estimating the overall, long-term effects of metabolic heat production in a real bird and egg. Secondly, we looked at the development of thermoregulation in a ground- nesting shorebird. An issue of general importance with regard to the ontogeny of precocial chicks is the timing of the onset of independent thermoregulation. We wanted to determine the mass at which crowned plover (Vanellus coronatus) chicks are able to thermoregulate independently in both the laboratory and the field, and to compare this to predicted values previously reported. Laboratory reared chicks attained independent thermoregulation at a mass of 65 g, while chicks in the field did so at a mass of 55 g. This is 33 - 39% of adult body mass, or approximately twice that predicted for a 167 g shorebird chick. Development of homeothermy represents a trade-off between growth rate and development of thermoregulation. Efficient use of behavioural thermoregulation, coupled with predation risks, allows more energy to be channelled into growth early on in the development of crowned plover chicks. Development of homeothermy in anyone taxonomic group may not, therefore, always be described by a single function. Instead , differences reflect a balance between growth rate, development of physiological thermoregulation, use of behavioural thermoregulation, predation risk, and environmental factors.
Urban ecology of the crowned eagle stephanoaetus coronatus in KwaZulu-Natal, South Africa.
(2015) McPherson, Shane Cameron.; Downs, Colleen Thelma.; Brown, Mark.
Urban environments comprise a complex and dynamic landscape, and urban sprawl is irreversibly transforming large areas of land globally. Increasingly, the need for incorporating ecosystem services into urban landscapes provides opportunities for green-space to benefit biodiversity and indigenous wildlife. Enhancing urban green-space maximises indigenous biodiversity and provides conservation value, and can also benefit people by enriching their experience and awareness of nature. Large charismatic species can stimulate awe and interest as emblematic representatives of the wilderness. As the global population becomes ever more urban, this enriches the human experience. The crowned eagle (Stephanoaetus coronatus) is a large predatory raptor and a threatened species that is increasingly known to inhabit the Durban Metropolitan Open Space System (D’MOSS), within eThekwini municipality, KwaZulu-Natal (KZN), South Africa. This research investigated the ecology of the crowned eagle in the urban environment and suggests opportunities for enhancing the urban landscape for conservation benefits. Globally, dramatic land use change typical of urbanisation negatively affects biodiversity, especially for top predators. The D’MOSS design faces the challenge of conserving biodiversity in a regional hotspot in the face of rapid urban growth in one of Africa’s major commercial hubs. Understanding habitat use of keystone and apex species provides urban planners with an opportunity to integrate biodiversity in a growing city. Consequently, we investigated habitat use and nest site selection of crowned eagles on various spatial scales within this urban mosaic. Unexpectedly the inter-nest distances were small in this human-dominated landscape. However, breeding sites were not evenly distributed through the landscape and were closely associated with natural forest, while nest trees were most frequently in patches of exotic large riverine Sydney blue gum (Eucalyptus saligna, Smith 1797) within the D’MOSS planning zones. Crowned eagles showed a strong tendency to avoid informal settlement areas, however they were tolerant of proximity to established formal settlements and occupied dwellings. Further, home range and habitat selection were investigated with GPS telemetry, albeit with a limited sample size (n =5) due to the limitations of abundance and dispersion of this apex predator. The 350 km2 urban core study area comprised a matrix of mainly formal settlements (44%), and DMOSS green space areas (29%). The study area was occupied by up to 22 active breeding pairs of crowned eagles. We documented a mean (n = 4) annual home range of 13 km2 (hull100%) containing 6.3 km2 of territory per pair (LKDE HLSCV 95%). These relatively small home ranges for a large eagle included shared territorial boundaries. Rapid replacement of vacancies at breeding sites suggests a saturated population. Habitat selection within the home range, thresholds of critical habitat, exotic trees, and correlation with DMOSS show the importance of pockets of indigenous forest in this urban mosaic landscape. These forests are fragmented and fragmentation increases the available edge habitats and landscape heterogeneity, potentially enhancing resource availability for crowned eagles in a highly modified landscape. The presence of remnant patches of mature Eucalyptus was more preferred than monotypic timber plantation stands. Consequently, continued protection of the D’MOSS system, and a considered approach to management of Eucalyptus are required for the persistence of the crowned eagle in this landscape The study of diet is pivotal in understanding a species, particularly for quantifying a predatory raptors’ economic niche and potential for human-wildlife conflict. In close association with urban development, the local population of crowned eagles has the potential to be a concern to the safety of domestic stock and pets. Time-lapse cameras were positioned at urban nest sites (n = 11) to identify the prey composition during breeding, particularly in regards to taxa with human associations. This was the first use of this technique for this species. The numerical proportion of avian prey, particularly hadeda ibis (Bostrychia hagedash) pulli, was several times greater than any previous diet description. The methodology used and the abundance of hadeda ibis in these urban environments are potential contributing factors. Rock hyrax (Procavia capensis) was the primary prey and where hyrax were unavailable, the diet composition was broader and included more vervet monkeys (Chlorocebus pygerythrus). Domestic stock comprised only 6% of the identifiable prey. Contrary to popular belief, no dogs (Canis familiaris) and few cats (Felis catus) were delivered to the nest by breeding eagles in this study. In situ pet attacks are most frequently attributed to juvenile and immature crowned eagles in winter and spring. Attacks on pets by crowned eagles, especially on small dog breeds, although relatively rare have a substantial influence on human-wildlife conflict and public perceptions. Pet attacks are generally attributed to juvenile and immature crowned eagles during periods of limited resources, particularly winter and during dispersal in the juveniles’ first spring. Negative social perceptions have resulted in persecution (n = 5), one of the main causes of recorded injury and mortality to crowned eagles in the region. Gunshot persecution, electrocution and collisions with anthropogenic structures have the greatest impact on juvenile and immature survival in the region. We provide management recommendations regarding various categories of crowned eagle human-wildlife interactions. Collaboration of wildlife authorities with NGO’s and public stakeholder input creates an environment for successful crowned eagle conservation and management of human-wildlife conflicts. Public awareness is an important aspect to the sustainability of the urban crowned eagle population. This study demonstrates that urban mosaic landscapes can provide conservation benefits for the crowned eagle. The land planning strategies enacted in Durban can guide urban expansion in tropical forest biomes to enhance indigenous biodiversity in urban mosaic landscapes in Africa, and globally.