No abstract available. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1987.

Thesis (Ph.D.)--University of Wyoming, 2008. / Title from PDF title page (viewed on August 9, 2009). Includes bibliographical references (p. 160-199).

Thesis (Ph. D.)--Ludwig-Maximilians-Universität München, 2006. / Title from PDF title page (viewed on June 4, 2006). Includes bibliographical references.

The small size of nectarivorous birds is associated with high mass-specific metabolic rates and energetic lifestyles. Their energy balance is likely to be strongly influenced by environmental factors. Firstly, nectar varies in sugar concentration between different food plants and birds must adjust their consumption to maintain a constant energy intake. Secondly, unfavourable weather conditions, such as storms and heavy rains, may prevent birds from feeding, and they must increase their energy intake to compensate for the loss in foraging time. Low ambient temperature, as a third energetic challenge, results in higher energy demands for thermoregulation, which leads to increased food intake. However, these compensatory feeding responses may be constrained by physiological limitations to nectar ingestion, digestion and osmoregulatory processes. My research focused on the behavioural and physiological responses of captive sunbirds (Nectariniidae) and honeyeaters (Meliphagidae) to energetic challenges, namely variations in nectar quality and availability and in ambient temperature. For sunbirds, I also investigated on a novel short-term scale how feeding patterns are adjusted in order to compensate for alterations in energy intake or requirements. Feeding events were recorded using a photodetection system, and body mass was monitored continuously by connecting the perches to electronic balances, interfaced to a computer. Whitebellied sunbirds (Cinnyris talatala) were fed various nectar sugar concentrations. Their feeding durations were found to provide an estimate of meal size on all food concentrations. When exposed to a decrease in sugar concentration, birds generally demonstrated an increased feeding frequency and food intake within 10 min. The number and duration of meals increased in the first few minutes after return of a more concentrated diet. When whitebellied sunbirds and brown honeyeaters (Lichmera indistincta) were exposed to a 2 h fasting period during the day, they increased their nectar intake and energy accumulation after the fast. Sunbirds achieved this by increasing meal size but not meal frequency. However, both species weighed less in the evening following the fast than the previous evening, indicating that the compensation for lost foraging time was incomplete. During acute cold exposure, whitebellied sunbirds, amethyst sunbirds (Chalcomitra amethystina) and brown honeyeaters increased their nectar intake, but lost body mass irrespective of nectar sugar concentration. Honeyeaters ingested more food at subsequent cold exposure, suggesting physiological adaptation to high feeding rates. A chemical reactor model of digestive capacity, which assumes sucrose hydrolysis to be the limiting step in nectar digestion, accurately predicted maximal food intake in honeyeaters, but mostly underestimated it in sunbirds. Sugar assimilation efficiency was higher than 99% in whitebellied sunbirds and brown honeyeaters. Lastly, licking frequencies and tongue loads of whitebellied and amethyst sunbirds were investigated. In both species, tongue lick duration increased, and licking frequency and consumption per lick decreased, with increasing nectar concentration. Birds did not adjust their licking behaviour after a fasting period. In conclusion, the response to varied energy challenges is shaped by both compensatory feeding and physiological constraints. Although unrelated, sunbirds and honeyeaters showed convergence in their responses, probably due to their similar nectarfeeding lifestyle. / Thesis (PhD)--University of Pretoria, 2009. / Zoology and Entomology / unrestricted

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. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

Made available in DSpace on 2016-06-02T19:26:21Z (GMT). No. of bitstreams: 1 SILVA_Bruna_2012.pdf: 2724610 bytes, checksum: fe28e8afc06ce2b8c55372a0dbc428ee (MD5) Previous issue date: 2012-04-13 / The availability of food resources in different degrees of regeneration of a forest may contribute to possible variations in species abundance and composition of bird communities. The main objective of this study is to investigate the relationship between the structure of frugivores and nectarivores bird communities and the availability of food resources - flowers and fruit - in two successional stages of regeneration (initial-secondary and advanced) of the Atlantic Forest. To reach this goal, frugivores and nectarivores birds were monitored in representative sites of these stages, considering seasonality and production of flowers and fruits at each stage over a year. The frugivores and nectarivores were compared in richness, species composition, relative abundance and diversity. We used fixed point counts for sampling birds, and to estimate the production of flowers and fruits, we delimited three replicates of four plots (10x10m) at each stage of succession. The two studied successional stages differed significantly in most of the analyzed vegetation structure variables. The composition and relative abundance of some bird species also showed differences between the two stages of regeneration, but not quantitative parameters as richness and diversity. There were variations in plant community phenological curves and in the amount of the floral production between the two successional stages. The relative abundance of frugivores had a significantly positive relationship with the amount of available ripe fruits. In the advanced stages, the relative abundance of nectarivores birds had a significantly positive relationship to the number of individuals of flowering epiphytic plant species; while in secondary stages of regeneration there was no change in the abundance of nectarivores birds in response to floral resource availability. Thus, in areas that are not continuous to primary forests may occur in a declining population of frugivorous and nectarivorous birds in response to variations in the phenological curves and food shortages causing changes in the processes of breeding and selection of plant species, which can bring significant implications for the conservation of birds and plants. / A disponibilidade de recursos alimentares em diferentes graus de regeneração de uma floresta pode contribuir para possíveis variações na abundância de espécies e na composição da comunidade de aves. O objetivo principal deste estudo é investigar a relação entre a estrutura das comunidades de aves frugívoras e nectarívoras e a disponibilidade de recursos alimentares flores e frutos em dois estádios sucessionais - secundário-inicial e avançado - de regeneração de Mata Atlântica. Para isso, a avifauna frugívora e nectarívora foi monitorada em áreas representativas desses estádios, tendo sido considerada a sazonalidade e a produção de flores e frutos em cada estádio ao longo de um ano. Os frugívoros e nectarívoros das duas comunidades foram comparados em relação à riqueza, composição de espécies, abundância relativa e diversidade. Foi utilizado o método de pontos fixos para a amostragem da avifauna e, para estimar a produção de flores e frutos, foram demarcadas três repetições de quatro parcelas (10x10m) em cada estádio de sucessão. Os dois estádios sucessionais estudados diferiram significativamente na maioria das variáveis de estrutura da vegetação analisadas. A composição e abundância relativa de algumas espécies de aves também apresentaram diferenças entre os estádios de regeneração, mas não nos parâmetros quantitativos considerados para as avifaunas como a riqueza e diversidade. Houve variações nas curvas fenológicas da comunidade vegetal e na quantidade de recurso floral produzido entre os dois estádios sucessionais. A abundância relativa de aves frugívoras teve uma relação significativamente positiva com a quantidade de frutos maduros produzidos. As aves nectarívoras, em estádios avançados, tiveram uma relação significativamente positiva de sua abundância relativa com o número de indivíduos de espécies vegetais epífitas em floração, enquanto que em estádios secundários de regeneração não houve alteração na abundância das aves nectarívoras em resposta a disponibilidade de recursos florais. Assim, em áreas que não são contínuas a matas primárias pode ocorrer um declínio na população de aves frugívoras e nectarívoras em resposta a variações nas curvas fenológicas e escassez de alimento gerando alterações nos processos de reprodução e seleção de espécies de plantas, o que pode trazer implicações significativas para a conservação de aves e plantas.