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The aim of my PhD research was to investigate how avian behaviours may be constrained by eye design and visual capabilities. As great diversity exists across bird species in the design of the visual system, I utilised this variation to examine and explain the links between vision and behaviour. Several methods were employed in order to gain ocular information from species: including measuring eye size, retinal image brightness and retinal topographic analysis. I applied and developed these methods in studies ranging from a microscopic scale analysis of retinal structure, to studies comparing whole eye size and morphology, to gain an insight into how the timing of different behaviours may be constrained by visual capability, and how artificially modified visual constraints can lead to behavioural plasticity. Specifically, I compared the visual ability of extant diurnally and nocturnally active avian species with that of Archaeopteryx, finding that this early bird was likely to have been diurnal in the timing of its activity. Following on from this, I found that eye size, controlling for body mass, is an important predictor in the timing of onset of dawn song for species around the world. This relationship is stronger in circumstances when twilight length is longer. This study also revealed how species richness may affect the timing of behaviours, suggesting that tropical birds are able to partition their dawn choruses to reduce masking of acoustic signals. When the presence of artificial lighting modifies the visual constraints at twilight and night, I found that European robins Erithacus rubecula correspondingly modified their singing, foraging and mass regulation behaviour. Overall, my research highlights the great diversity of avian visual adaptations, and emphasises that understanding the differences between them is intrinsic to appreciating the way in which behaviour is constrained by visual ability.

The aim of this thesis was to evaluate the proposal by Miller and Shettleworth (2007) that learning about geometric cues in environments with a distinctive shape is governed by a competitive learning rule (e.g., Rescorla & Wagner, 1972). To do this, in all experiments, rats were trained to locate a hidden platform by reference to the shape of a swimming pool. Chapter 2 (Experiments 1 -4) assessed whether a landmark suspended above the platform would overshadow learning about geometric cues. No overshadowing was recorded, even when the salience of the geometric cues was reduced. These findings are inconsistent with the model of Miller and Shettleworth (2007). In Chapter 3 (Experiments 5-7), a blocking paradigm was used. When rats were given extended pre-training with a landmark above the platform, only then did the landmark successfully block learning about geometric cues. However, some unexpected findings suggested that perhaps the spatial cues were competing for attention rather than associative strength. The experiments in Chapter 4 (Experiments 8 and 9) successfully demonstrated superconditioning of geometric cues by an inhibitory landmark providing convincing evidence that learning about geometric cues is governed by the principles of associative learning. Miller and ShettlewortiVs (2007) model however, failed to predict this outcome. Experiments 10-13 in Chapters 5 and 6 showed that associations formed between geometric and non-geometric cues. This outcome provides the basis for a viable explanation for potentiation and for the past failures to find cue competition in the spatial domain. The empirical findings of this thesis show that learning about geometric cues is not entirely void of associative processes as once thought. A number of recent models of spatial learning are discussed.

This thesis investigated differences in foraging behaviour, personality and parasitic infection, using behaviour experiments, traditional parasitology and molecular ecology. Five fish species, and a directly-transmitted ectoparasite, were used as model organisms. Evidence for a conservative foraging strategy was found in the four tropical fish species (Poecilia reticulata, P. sphenops, Xiphophorus maculates, X. hellerii) and in a temperate species (Gasterosteus aculeatus). In the latter, this behaviour was unaffected by social context, with no significant differences between isolated fish and shoals. Also, guppies showed a reduced acceptance of novel, conspicuously-coloured prey. Furthermore, using molecular scatology techniques, both prey and host species-specific DNA were detected in fish faecal samples so this methodology can be used in the future to examine diet in the wild. When considering the personality trait, boldness, guppies from two wild populations differed significantly in their relative boldness, but individuals within a single population were similar in their relative boldness. Boldness of fish was affected by mating, with virgin and pregnant females being bolder than their mated counterparts. Also, boldness impacted on shoaling behaviour, shy fish formed larger and tighter shoals than bold conspecifics. This had consequences for parasite transmission, with shy fish having higher parasite loads and a greater change in parasite load across an infection period than their bold counterparts. Furthermore, host contact was the main factor influencing transmission of a directly-transmitted ectoparasite within a group-living host species. Significantly more parasites were transmitted between hosts when hosts had more frequent and more prolonged contact with each other. Clearly, monitoring individual differences in various aspects of an animal's behaviour can answer many questions of ecological relevance, as well as discovering the evolutionary origins of such individual behavioural traits.

The prevalence of a parasitic nematode of slow worms, <italic>Neoxysomatium brevicaudatum,</italic> was also investigated using PCR primers. Prevalence was higher in males and females in April. Analysis of smooth snake diet confirmed that predation on reptiles was high but revealed increasing consumption of small mammals with age. Predation on reptiles by grass snakes was higher than expected and suggests competition may exist between smooth snakes and grass snakes at a juvenile stage. Overall, these results provide information pertinent to translocation and reintroduction programmes along with conservation management strategies.

Begging signals given by nestling birds may advertise their condition or quality and parents may respond by allocating their resources in relation to begging intensity. In order for such signals to be honest, they must be costly to produce. The aim of this project was to investigate the role of nestling endogenous testosterone (T) as a potential mechanism to control begging signals in pied flycatchers, Ficedula hypoleuca. Androgen levels were analysed from invasive and non-invasive (faecal) samples using T radioimmunoassay. In the laboratory, nestling begging behaviour was measured as: 1) the duration of begging displays and 2) the maximum height of begging stretches. It was found that individual nestlings begging most intensively had the highest circulating levels of T immediately after testing. This relationship was tested experimentally by dosing nestlings with oral doses of T and assessing the effects on nestling begging signals. The results showed that the duration of begging displays by T-dosed nestlings were longer than controls, confirming the causal nature of T in controlling nestling begging signals. A field study investigated the effect of brood reduction on parental provisioning strategies, nestling behaviour and T levels. During brood reduction parents allocated food resources according to rules based more strongly on nestling begging behaviour compared with control days. A partial cross-fostering experiment tested whether nestling T and begging behaviour related to levels of relatedness within the nest. The begging duration of cross-fostered broods was longer than control broods and fostered nestlings increased their faecal androgen levels, although the reliability of this result should be further investigated. A biochemical validation study confirmed that excreted androgen metabolites were measured in the faeces of pied flycatchers. Overall, the results of this project confirmed that T is responsible in part for the control of begging intensity and may be a mechanism that controls begging behaviour in nestling birds.