Thesis (Ph. D.)--Oregon State University, 1990. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

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A central question in behavioural and evolutionary ecology is to understand how animals make decisions between, for instance, potential mates, nesting sites, foraging patches and territories. Normative models of choice usually predict preferences between alternatives by computing their value according to some criterion and then identifying the alternative with greatest value. An important consequence of this procedure is captured in the economic concept of rationality, defined through a number of principles that are necessary for the existence of a scale of value upon which organisms base their choices. Violations of rationality are nonetheless well documented in psychological and economic studies of human choice and consumer behaviour, and have forced a reinterpretation of much of the existing data and models. Although largely unexplored in the study of animal decision-making, the systematic observation of irrationality would similarly pose serious challenges for functional approaches to behaviour. In this thesis I explore the possibility that violations of rational axioms may also be found in animal choices, using the European starling (Sturnus vulgaris) as a model species. My objectives were threefold. Firstly, I investigated the prevalence of rationality across distinct foraging paradigms, in situations involving multialternative choices, structured choice sets, choices between alternatives described by multiple attributes and risk-sensitive decisions. In a number of distinct experiments, the preferences of the starlings were consistent and stable across contexts, conforming to basic rational principles such as transitivity and regularity. A second objective was to explore possible factors underlying reported violations of rational axioms by animals. Amongst potential mechanisms, I review and examine the implications of the use of hierarchical and higher order choice rules, as well as the presence of constraints on the perception of rewards. Finally, I examine the likely effect of contextual changes on an organism's state, and consequently choice behaviour, and experimentally confirm the expectation that statedependence in foraging preferences can underlie the observation of seemingly irrational behaviour. Altogether, my results suggest that, rather than being a common phenomenon, breaches of rationality in animals might be restricted to specific sets of parameters and conditions. They also emphasize the importance of considering the potential multitude of factors underlying violations of rationality in animal choices, and suggest that students of economic rationality in animal behaviour should also view preferences as a dynamic, statedependent measure.

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Global climate change is expected to increase the frequency of extreme and unpredictable weather in many parts of the world. As a result, a critical goal for biologists is to predict how organisms may come to cope with increased environmental variability. The key to making these predictions will be to understand how animals currently living in fluctuating environments are able to survive and reproduce under these conditions. Sociality (i.e. group living) and cooperative breeding (i.e. where more than two individuals care for young together) may both facilitate the colonization of highly fluctuating environments. However, the relative benefits of group living and engaging in alloparental care under variable conditions remain unclear. My dissertation examines the fitness consequences of living in one of the world’s most unpredictable habitats—the African savanna—in a population of free-living cooperatively breeding superb starlings (Lamprotornis superbus). In chapter 1, I examine whether adults benefit from living in large social groups of up to 50 individuals, which are among the largest known for any cooperatively breeding bird. In addition, I test whether group size serves to buffer against harsh environmental conditions. In chapter 2, I examine whether breeders gain reproductive benefits by having alloparents at their nest—I explore the type of reproductive benefits gained (i.e. improved reproductive success versus offspring care load-lightening), as well as whether these benefits occur in both harsh and benign conditions (i.e. temporal variability hypothesis), or are greatest under harsh conditions only (i.e. hard life hypothesis). In chapter 3, I explore whether offspring care load-lightening reduces the cost of reproduction incurred by breeders and alloparents by comparing four physiological mechanisms known to mediate reproductive costs. Lastly, in chapter 4 I test the long-standing assumption that cooperatively breeding species face reduced costs of reproduction by sharing offspring care relative to non-cooperatively breeding species. I compare the oxidative cost of reproduction in superb starlings to greater blue-eared glossy starlings (L. chalybaeus), a synoptic non-cooperatively breeding species. Taken together my dissertation findings demonstrate that group living and alloparental care do not solely buffer against harsh conditions in superb starlings, but instead provide individuals with the flexibility to modify their offspring care behavior according to environmental conditions, to the behavior of other group members, and to their physiological condition prior to breeding—this behavioral flexibility may in turn serve to mitigate fluctuations in the cost of living and breeding in variable environments.