This thesis addresses decision mechanisms in foraging situations, using laboratory experiments with European starlings (Sturnus vulgaris). Building on previous work from the Behavioural Ecology Research Group, I chose the Sequential Choice Model (SCM; reviewed in Kacelnik et al., 2011 − Appendix 1) as a starting point, and tested its premises and predictions generalising it to different experimental protocols. Classical decision models do not relate choice preferences to behaviour towards isolated options, and assume that choices involve time-consuming evaluations of all alternatives. However, previous work found that starlings’ responses to isolated options predict preference in choices, and that response times to single-option encounters are not reliably longer than response times in choices. Since, in the wild, options are normally encountered sequentially, dealing with isolated options can be considered of greater biological, and possibly psychological, significance than simultaneous decisions. Following this rationale, the SCM postulates that when multiple simultaneous stimuli are met they are processed in parallel, each competing against the memory of background opportunities, rather than comparing present options to each other. At the time of launching this research, these ideas had only been applied to protocols involving just two deterministic alternatives and offering no chance to explore the influence of learning history (i.e., how animals learn to choose; see Chapter 4). To increase their relevance and offer more rigorous tests, I generalised them to situations with multiple (see Chapters 2, 4 and 5), and in some cases probabilistic alternatives (see Chapter 3), controlling the learning regime. I combined these extensions with tests of economic rationality (see Chapter 6), a concept that is presently facing sustained debates. Integrating the result of all experimental chapters (see Chapter 7), my results support the notion that behaviour in single-option encounters is fundamental to understand choice behaviour. The important issue of whether choices involve a decision time cost or the opposite, a shortening of response times, remains unsolved, as neither could be evidenced reliably.

The main object of this study was to investigate the effects of predation by starlings (Sturnus vulgaris) on populations of the grass grub (Costelytra zealandica) in Canterbury, with the secondary objective of investigating the feasibility of life table studies of grass grub populations under Canterbury conditions. Study plots were established in four areas, two on non-irrigated pastureland at Lincoln and Weka Pass and two on irrigated pastureland at Winchmore. A third study plot was established at Winchmore in the second year of field work.