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Several papers on the microscopical structure and the pigmentation of the feathers of the Budgerigar have already been published. This bird which is so easily bred and which, under selection, has developed a great number of varieties in two or three decades and practically from the beginning under scientific control, is an object of intense interest for the geneticists. Its varieties differ predominantly by their shades of colour. The subjective impression of a colour, however, is not a criterion sufficiently reliable for distinguishing the varieties. Partly for this reason, but chiefly in order to establish the effects of the genetical factors on both structure and pigment, the researchers included the microscopical examination of feathers and feather-germs in their field of work. Nevertheless, further research along these lines has been found desirable, chiefly for two reasons. First, since the publication of the papers referred to a number of new varieties has appeared with shades of colour very different from those known hitherto. These shades suggest that there may be very interesting changes in the structural and pigmentary factors which are responsible for the impression of colour. Secondly, these authors did not undertake a histological investigation of the feathers and feather-germs which could be considered exhaustive from a purely morphological point of view, as they were chiefly concerned with genetical problems. Moreover, these papers reveal differences in the histological interpretation of the examined material.

Similarities in brain size, life histories, psychology and behaviour in parrots, corvids and apes suggest that certain socio-ecological selection pressures may have driven the convergent evolution of cognition in these families. However, very little is known about parrot behaviour and cognition, outside of African greys and kea. Therefore, captive red-shouldered macaws (Diopsittaca nobilis) and black-headed caiques (Pionites melanocephala) were presented with a variety of tasks to assess their social and physical cognition and behavioural flexibility. Although these species possess many similarities in their life history and ecology, there are also substantial differences in their morphology and natural habitats that could have driven differences in their cognitive evolution. Observations of social and physical interactions in both species revealed that macaws engaged in high levels of affiliative behaviour, and object neophobia, whereas caiques displayed high levels of social play and object exploration. However, such differences did not appear to result in differences in their social or physical cognition. Macaws and caiques displayed comparable performances on Serial Reversal Learning tasks (as an index of behavioural flexibility). Both species also demonstrated similar performances on two Means-End transfer tasks and a series of innovative foraging tasks that were designed to assess their comprehension of object relationships. However, macaws and caiques appeared to solve such problems by generalising learned information across novel tasks. Overall, these findings suggest that these two species may approach certain socio-ecological problems using flexible cognition that may be generalised across different problems, supporting claims for a domain general intelligence.

Many animals are social foragers. Foraging with others may confer a number of advantages, but is also likely to present a number of challenges that are not encountered by solitary foragers. For instance, whilst feeding in a group may interfere with an animal's ability to learn new foraging skills or the location of new foraging patches by itself, it may simultaneously provide it with the opportunity to acquire new skills or knowledge by means of social learning. This thesis addresses a number of questions relating to the interaction between social foraging and social learning using small groups of captive budgerigars, Melopsittacus undulatus, as a test species. In particular, it investigates the spread of novel foraging behaviour through groups of birds under conditions that either permit or restrict a high degree of ‘scrounging' (food stealing) by naïve birds from skilled ‘producers' in their group (Chapter Three). Scrounging is found to inhibit naïve budgerigars' performance of new foraging skills, but appears to facilitate their underlying acquisition, or motivation to acquire these skills, when the need arises – for instance, when producers are lost from their group. In addition, the thesis assesses the importance of a number of different individual-level characteristics, such as age, sex, and competitive rank, in predicting birds' propensity to behave as producers rather than scroungers when foraging in a group (Chapter Four). The thesis also examines budgerigars' relative use of social and personal information when selecting foraging locations (Chapter Five), and assesses the importance of group social networks in predicting individual birds' order and latency to arrive at foraging patches (Chapter Six). Budgerigars are found to rely on social information when they lack any personal information about foraging locations. When equipped with both social information and personal information, some, but not all birds appear still to utilise social information. Birds' social networks appear to have little bearing on individuals' foraging patch visitation times.