The role that climate plays in the ecology of organisms is perhaps the most pronounced where the earth’s environments are most extreme. In arid-zones, organisms have to deal with large seasonal shifts and/or extremes in temperature and/or moisture levels. As a result, arid-zone species are sensitive to climatic changes. I assessed the physiological and behavioural adjustments of an arid-zone endemic passerine, the rufous-eared warbler (Malcorus pectoralis), to seasonal changes in the Karoo semi-desert of South Africa. Respirometry measurements in the field showed that the warblers’ basal metabolic rate was lower and set point body temperature (Tb) was higher in summer compared to winter. At high air temperatures (Ta) evaporative water loss (EWL) rate was significantly lower in summer compared to winter, while Tb showed a clear pattern of heterothermy that was similar in both seasons. Compared to winter, the warblers in summer were able to remain calm, and tolerate higher Ta’s, before their Tb’s increased to potentially detrimental levels. Behavioural observations showed that free-living warblers exhibited significant temperature-dependence in their behaviour; they increased panting behaviour, and reduced activity levels, time spent preening, and foraging effort at high Ta’s in summer. The warblers also displayed a considerable decrease in foraging success, and a shift in microsite use, at high Ta’s in summer. I hypothesise that the flexible responses the rufous-eared warblers show are aimed at increasing their heat tolerance in summer, and help them balance their energy and water demands in an arid environment that exhibits wide seasonality in Ta, in addition to high summer Ta. My findings emphasise the importance of identifying, as well as understanding, the associated costs of physiological and behavioural responses to environmental variables. This information is valuable in terms of predicting biologically meaningful responses (and hence, vulnerability) of arid-zone avian communities to climactic shifts.

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State-dependent life history theory predicts a trade-off between an individual's state and reproductive effort. The identification and effects of key state variables, however, have not been explored empirically in depth. Although there are some studies which have provided evidence that state-dependent behaviour indeed occurs, the bulk of this work is neither experimental, nor related to reproduction. Furthermore, the quantitative effects of manipulations of specific state variables are invariably unknown (McNamara & Houston 1996). This thesis explores potential trade-offs between state and behaviour and determines if energy reserves can be employed as a useful state variable. In contrast to other empirical studies, parental states (energy reserve at dawn) were experimentally manipulated using a direct method, namely changes in overnight temperature (Warming, Chilling and Control). The effects of these temperature changes were quantified using indirect calorimetry. Responses to these experimental manipulations were measured by behavioural observations, a common method in behavioural ecology, but were also quantified in terms of energy expenditure, with the aid of the doubly labelled water technique. Thus, this thesis provides a unique quantitative approach, in that it measures both manipulations and responses in the currency of energy. Individual energy reserves at dawn significantly affected resource allocation decisions the subsequent day. Birds with surplus energy upon release increased the number of feeding visits to their nestlings whilst in parallel increasing energy expenditure. Those with an energy deficit at dawn, conversely decreased nest visitation rates along with energy expenditure. There were no effects of temperature manipulations upon mass or fatscore changes over the trial period, suggesting a regulation of somatic investment at a threshold level, whilst reproductive effort was varied depending on parental state. The responses to positive manipulations (warming) were congruent across two species with differing foraging ecologies: the swallow, an aerial feeder foraging in a variable environment; and the great tit, foraging in relatively stable woodland. Thus, the behavioural and energetic responses seen here were not the result of species-specific strategies. This points the way towards a general rule within state-dependent behaviour. The trade-off identified here implies that reproduction carries a cost, and that reproductive effort will be reduced if an animal's survival is jeopardized and vice versa: a life history response, mediated by an individual's body-state. Furthermore, the response of birds to positive and negative manipulations was large enough to be readily detected, even amongst the considerable variation in energy expenditure related to individual differences. This suggests that body-state not only plays a key role in allocation decisions, but that it is comparable in the scale of its effects to other major influences on energy expenditure of free-living animals.

Part One is an investigation of the dawn chorus in the Great Tit. The major conclusions are as follows: Foraging and singing are partly incompatible because of the temporal and spatial separation of microhabitat conditions required for each activity. The dawn chorus occurs at a time of day when: a) foraging efficiency is limited by low light intensity and possibly by lack of mobility of the prey due to low temperature; b) acoustic communication is more efficient than visual displays because of poor visibility and an enhanced sound transmission; c) the rate of territorial intrusion is at its daily peak. Great Tit's readiness to sing and react agonistically towards a territorial intruder is enhanced by experimentally lowering profitability of feeding, but it does not appear to be affected by time of day. Restricting access to food early in the morning leads to higher body weight in the evenings as an anticipatory compensation. Part Two is a study of sampling strategies based on the statistical decision paradigm known as the Two-Armed Bandit problem. I studied transition behaviour in foraging experiments using concurrent variable ratio schedules. The birds' foraging behaviour approximated the predictions of a dynamic programming algorithm that calculates the optimal balance between exploring and exploiting for finite time horizons. The birds' response to patch diversity and time horizon was closer to molar maximization (total rewards over a certain period) than to molecular maximization (maximising the instantaneous probability of reward). When the environment is not totally stable these two possibilities conflict, and my results supported molar maximization. Part Three investigates the trade-off between maximising foraging efficiency and efficient territorial defence. Great Tits behaved close to the predictions of the Marginal Value model when there were no territorial intrusions, but modified their feeding behaviour in the predicted way when the probability of intrusion was higher.

Orientador: Reginaldo José Donatelli / Coorientador: Carlos Barros de Araújo / Banca: Luiz Octavio Marcondes Machado / Banca: Fátima Knoll / Resumo: O capítulo teve como objetivo descrever o comportamento reprodutivo de Pionites leucogaster leucogaster e Pionites melanocephalus melanocephalus em cativeiro. Para isso foram coletados dados a partir de observações dos comportamentos das aves dentro e fora dos ninhos, principalmente durante a estação reprodutiva. Para a obtenção de dados do interior da caixa ninho, foram instaladas câmeras de infravermelho no interior dos mesmos. Dentre os comportamentos associados à reprodução foram constatados, para ambas as espécies: a corte (exceto para Pionites m. melanocephalus), o cortejo alimentar, a cópula e o cuidado dos pais para com a prole, além de outros dados biológicos como a postura dos ovos, o período de incubação e a eclosão. Verificamos que as fêmeas das espécies estudadas realizam a postura de quatro ovos e são exclusivamente responsáveis pela incubação dos mesmos, neste período, são totalmente dependentes do macho com relação à alimentação. As marianinhas apresentam períodos longos de incubação e a eclosão dos ovos ocorre de forma assincrônica. Comportamentos como cortejo alimentar (registrado somente na fase de pré-postura), a transferência de alimento e o alisamento das penas (comportamentos muito observados durante toda a estação reprodutiva) são importantes interações que têm papel fundamental na manutenção da coesão entre o casal. Além de utilizarem o ninho na estação reprodutiva, as marianinhas utilizam as cavidades como dormitório durante todo o ano / Abstract: Not available / Mestre

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