Existing research on the foraging ecology and breeding biology of blue tits (Cyanistes caeruleus) and great tits(Parus major) has mainly concentrated on populations in woodland. However increasing urbanisation means much of the suitable tit habitat is represented by fragmented areas, not large woodlands, and little is known about factors that may affect reproductive success in urban environments. Using General and Generalised Linear Models this study compared reproductive performance in four habitat types with differing levels of habitat modification: the Cambridge University Botanic Garden (CUBG) with an abundance of non-native vegetation and structural fragmentation, two marginal sites with native scrubby vegetation and structural fragmentation and small fragments and large fragments of native woodland. Compositional analysis was used in a study focused on how foraging blue tits used the heterogeneous habitat of the CUBG. Additionally frequency tests were used to compare foraging preferences and foraging behaviours of both species in the CUBG. Productivity was poor in the CUBG compared to all of the other habitats, with great tits appearing to do worse than blue tits, rearing lower quality chicks (significantly lower mean mass than in other habitats). Within the CUBG, positive relationships were found between the abundance of native trees and shrubs and breeding success for both blue tits and great tits. A positive relationship was found between breeding success in blue tits and the abundance of Quercus and Betula. However, habitat and year interactions showed that habitat and reproductive relationships were complicated by annual variation. The two species differed in their foraging preferences in the CUBG; blue tits were observed feeding in native deciduous trees significantly more than in non-native species and had a preference for birch trees over other taxa. Great tits however showed no strong preferences for any of the habitat types. With regards to foraging behaviours, great tits used a wider range of foraging heights and different foraging locations and capture techniques than blue tits. Blue tits were observed‘hanging’ from twigs more frequently, and appeared to be more effective at foraging in the wider variety of plants available in the heterogeneous vegetation of the garden. The data presented in this thesis suggest that blue tits have adopted a better foraging strategy by preferentially choosing native deciduous trees over the abundance of non-natives available in the CUBG. However, despite the apparent better foraging strategy of blue tits, reproductive performance of both species is poor in this urban garden compared to marginal sites and woodland. Urbanisation and the associated loss of optimal tit habitat are likely to continue. It is therefore important to offset urbanisation by the addition of appropriate foraging habitats that are likely to improve reproductive success, such as native trees and shrubs.

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Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This study tested the proposal that fleshy-fruited alien shrubs competed more effectively for avian dispersal services than indigenous shrubs. Several different quantitative measures of increasing complexity were applied to test bird foraging preferences for fruits of two established alien shrubs (Lantana camara, Solanum mauritianum), two emergent alien shrubs (Myoporum tenuifolium, Pittisporum undulatum) and two indigenous shrubs (Chrysanthemoides monilifera, Olea europaea subsp. africana). Overall the simplest quantitative measure, namely that of bird visitation frequency identified foraging preferences of individual bird species for fruits of alien and indigenous shrubs. Moreover, even the more complex measures of numbers of foraging birds, foraging times and products of these in the computed consumption intensity and seed dispersal efficiency were positively correlated to visitation frequency. There was a distinct preference of several, especially heavily fugivorous, bird species for fruits of established alien than indigenous shrubs and several moderately fugivorous bird species preferred fruits of emergent than established alien shrubs. Intricate photographic and experimental approaches were applied to obtain precise numerical data on seed removal rates by birds from the alien and indigenous shrubs. Deficiencies associated with the experimental approach included its inability to discriminate between asynchronous fruit production and fruit ripening, individual foraging bird species, and fruit consumption by other fruit foraging vertebrates. The advantages of the photographic approach were in its provision of a detailed permanent record of individual foraging bird species, their total numbers and precise foraging times and the proportions of whole fruits consumed, as well as other behavioural foraging traits. Tested also was the proposal that frugivorous birds remove larger amounts of fruits from plants with high fruit production and nutritional contents and that the germination of the bird-ingested seeds is enhanced. In compliance with this proposal, canopy fruit mass and monosaccharide content were all positively correlated with the total numbers of seeds removed by birds and viable seeds excreted by birds. Only defecated seeds of the indigenous C. monilifera and alien L. camara displayed enhanced germination following their ingestion by birds Seed dispersal distances of alien and indigenous shrubs by birds were estimated from published records of bird body masses, gut retention times of consumed seed and flight speeds. Estimated seed dispersal distances ranged between 0.41 and 0.81 km for the subset of heavily and moderately frugivorous bird species examined. However, their foraging distances derived from birdring recapture records were much greater, these peaking between 2.5 and 50 km in some heavily frugivorous bird species. It is concluded 1. that bird visitation frequency be applied as the most efficient and practical quantitative measure for gauging bird foraging preferences in future surveys which should involve large complements of indigenous, emergent and established alien species, 2. that flight speeds and gut passage times of ingested alien and indigenous seeds need to be measured in local bird species so long distance seed dispersal potentials can be more precisely determined and 3. that control measures should be focused on eradicating especially emergent alien species with fleshy fruits from urban environments to prevent their transport by birds into adjacent natural areas. / AFRIKAANSE OPSOMMING: Hierdie studie het die voorstel getoets dat uitheemse vlesige-vrug struike meer effektief kompeteer vir voël verspreidingsdienste as inheemse vlesige-vrug struike. Verskeie kwantitatiewe maatstawwe van toenemende kompleksiteit was toegepas om die voedingsvoorkeure van voëls vir vrugte van twee gevestigde uitheemse struike (Lantana camara, Solanum mauritianum), twee ontluikende uitheemse struike (Myoporum tenuifolium, Pittisporum undulatum) en twee inheemse struike (Chrysanthemoides monilifera, Olea europaea subsp. africana) te toets. Algeheel het die eenvoudigste kwantitatiewe maatstaf, naamlik voël besoek frekwensie, voedingsvoorkeure van individuele voël spesies vir vrugte van uitheemse en inheemse struike geïdentifiseer. Addisioneel het die meer komplekse maatstawwe soos voël getalle, voedings tye, asook produkte hiervan in die berekende verbruiks intensiteit en saadverspreiding effektiwiteit almal positiewe korrelasies met besoek frekwensie. Predominant vrugtevretende voël spesies het ‘n duidelike voorkeur getoon vir vrugte van gevestigde uitheemse eerder as inheemse struike. Verskeie meer gematigde vrugtevretende voël spesies het egter vrugte van ontluikende eerder as gevestigde uitheemse struike verkies. Ingewikkelde fotografiese en eksperimentele benaderings was gebruik om presiese numeriese data van saad verwyderingstempo’s deur voëls vanaf die bestudeerde struike te bekom. Tekortkominge geassosieerd met dié eksperimentele benadering sluit in die onvermoë om te onderskei tussen asinkrone vrug produksie en vrug rypwording, individuele kos soekende voël spesies, asook vrug verbruik deur ander vrugvretende werweldiere. Die voordele van die fotografiese benadering was die verskaffing van ‘n gedetailleerde permanente rekord van individuele kos soekende voël spesies, hul totale getalle, presiese voedingstye, proporsie heel vrugte verbruik, asook ander voedingsgedrag eienskappe. Ook getoets was die voorstel dat vrugtevretende voëls groter hoeveelhede vrugte verwyder van plante met hoë vrugproduksie en hoë nutriënt inhoud, en dat ontkieming van voëlingeneemde sade verhoogd is. In nakoming met die voorstel, was blaredak vrugte massa en monosakkaried inhoud albei positief gekorreleer met totale aantal sade verwyder deur voëls en lewensvatbare sade uitgeskei deur voëls. Slegs sade van die inheemse C. monilifera en die uitheemse L. camara het verhoogde ontkieming gewys na inname deur voëls. Saadverspreiding afstande van uitheemse asook inheemse struike deur voëls was bepaal vanaf gepubliseerde rekords van liggaams massa, saad behoud tye in die maag na inname, en vliegspoed. Beraamde saadverspreiding afstande het gestrek tussen 0.41 en 0.81 km vir dié subgroep van predominant en gematigde vrugtevretende voël spesies bestudeer. Nogtans was voedings afstande, afgelei van geringde voël hervangs rekords, veel groter, en het gepiek tussen 2.5 en 50 km vir sommige predominant vrugtevretende spesies. Gevolglik weet ons nou dat 1) voël besoek frekwensie toegepas kan word as die mees effektiewe en praktiese kwantitatiewe maatstaf vir die bepaling van voël voedings voorkeure in toekomstige opnames waar komplementêre groepe inheemse, ontluikende en gevestigde uitheemse spesies bestudeer word; 2) vliegspoed en maag passeer tye van ingeneemde uitheemse en inheemse sade gemeet moet word in plaaslike voël spesies sodat langafstand saadverspreiding potensiaal meer presies bepaal kan word; en 3) beheer maatstawwe moet fokus op die verwydering van spesifiek ontluikende uitheemse vlesige-vrug spesies vanuit stedelike omgewings, om sodoende saad vervoer deur voëls na naasliggende natuurlike areas the verhoed.