Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Chapter 1 provides an introduction to the thesis by discussing the relevant literature on vocal learning in songbirds and parrots, with particular reference to calls, and setting out the aims of the following chapters. Chapter 2 concerned an investigation of the similarity in the distance calls within and between families of zebra finches, involving fostering young birds to non-related parents. Male offspring were most similar in their distance calls to their male siblings with which they were raised and the adult male which raised them, suggesting an environmental influence in the acquisition of the call. There was also an indication that the call may be, at least in part, inherited. Females were most similar to their mothers and female siblings, though not to the same extent as in males. Chapter 3 examined whether male zebra finches could exhibit vocal plasticity in adulthood, by learning new calls from other conspecifics, and whether social deprivation during a young bird's development would accentuate this tendency. Adult zebra finches could not learn new calls from other similarly raised cagemates, even if these birds were reared under conditions of extreme social deprivation and were presented with an appropriate normally-raised adult male tutor. Chapter 4 described a study which investigated whether adult male budgerigars housed in soundproof boxes, could learn new calls from a tape recording in the absence of any social stimuli. Learning from tapes was very limited with only one bird producing an accurate copy of the playback, emphasising the importance of an interactive social context in vocal learning. Chapter 5 attempted to determine exactly which social factors were most influential in determining the extent of call matching between adult male budgerigars. Certain individuals did match more closely in their contact calls; close proximity appeared to promote call convergence between cagemates. Chapter 6 examined the effect of adding an unfamiliar budgerigar to an established flock, on the group specific call. It was found that, contrary to expectation, mutual imitation by all flock mates did not occur as other studies have shown, and that 'new recruits' conformed to the shared group call. Chapter 7 concluded the findings of the five experimental chapters, and discussed their significance with reference to previous studies, including ideas for further investigation.

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.

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.