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Increasing deer populations across the northern hemisphere have been cited as one of the factors potentially contributing to declines in the populations of some woodland bird species, particularly species that are dependent on the shrub layer. This thesis examines the effects of browsing by deer on the use by birds of a regenerating deciduous woodland system eastern England, and investigates the mechanisms by which impacts operate. Using a replicated experiment, over the course of four years, habitat use by birds in exclosures without deer was compared with that in paired control plots. The latter plots were browsed by roe deer and Reeves's muntjac throughout the year (and fallow deer in winter). A range of ornithological survey methods were used to compare the habitat types, including point-counts, standardised mist-netting and radio-tracking. During the breeding season, the most marked negative responses to deer were shown by birds that are dependent on dense understorey vegetation, such as dunnock Prunella modularis, nightingale Luscinia megarhynchos and garden warbler Sylvia borin. Pertinently, browsing by deer has the potential to reduce habitat quality for woodland birds. Territories of nightingale became confined to vegetation where deer were absent and male blackcaps Sylvia atricapilla established territories earlier and were in better body condition there. Unbrowsed young re-growth (prior to canopy-closure) was particularly important during the post-breeding period for a range of species, presumably in response to foraging resources and protection afforded. Similarly, the first ever examination of responses of woodland birds to deer in winter, showed that several common resident ground-foragers, such as robin Erithacus rubecula, were negatively affected in winter having shown no effect in the breeding season.

Colonial breeding in birds is widely considered to provide a net benefit to individuals, outweighing costs such as increased competition for resources and intra- specific aggression. This view, however, is largely based on studies of seabirds carried out under favourable conditions. Recent breeding failures at many seabird colonies in the UK provide an opportunity to re-examine costs and benefits of coloniality under adverse conditions. In this thesis I show in the highly colonial Common guillemot Uria aalge how, during unfavourable conditions, the magnitude of these costs and benefits is dependent on the social environment of the breeding area. Parents were able to increase their foraging effort by leaving their chick unattended at the colony, but this unexpectedly resulted in heightened aggression towards unattended chicks from conspecifics, sometimes resulting in the chick being killed. However, despite the magnitude of this cost showing negative density-dependence, it did not result in diminished positive density-dependence of overall breeding success, suggesting that colonial breeding is still beneficial during unfavourable environmental conditions. Parents were also able to utilise a combined strategy of foraging at sea augmented by kleptoparasitism, stealing prey from neighbours, to increase chick provisioning rate and survival during adverse conditions, with no apparent cost to hosts. In contrast, cooperative behaviours were still evident, and I suggest that alloparental care, where an individual cares for unrelated young, is maintained via a combination of short- term benefits for the alloparent (additional parental experience) and chick (increased chick survival during periods of high parental non-attendance) and long-term benefits for the alloparent (future reciprocation of alloparental care). Investment in preening partners and neighbours was found to be negatively related to chick fledging success, suggesting that some cooperative behaviour may be disadvantageous during adverse conditions, when individuals apparently benefit more from investing in activities that directly increase reproductive success.

The aim of this project is to develop a method to successfully link together various sources of disparate information and data in order to study and understand which factors influence bird communities in different areas. For many areas, especially those of high conservation priority, an enormous amount of information and data may already be available. By using the right tools they could potentially be linked to provide improved understanding of the mechanisms that influence the biodiversity in a region of interest. To test this hypothesis I used structural equation modelling (SEM) to link data from Kakamega Forest in order to study the effects of various socio-ecological factors on the bird species richness in twenty-two different parts of the forest. Kakamega Forest is Kenya’s only rainforest and despite its rich biodiversity, and especially avian diversity, the forest is highly threatened with less than half of its area containing indigenous vegetation. A similar modelling approach is used to study the factors that influence migratory birds found in thirty-eight Natura 2000 sites in Cyprus, designated under the EU’s Habitats Directive (officially known as the Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora). Using GIS analysis and available data on land use, vegetation cover, habitat diversities, human population densities, and road densities, I developed a path model explaining the observed bird species richness in those areas. Through this type of analysis I identified and quantified the impact of various habitat variables on bird species richness, which is one of the many measures of species diversity. Compared to other diversity indices, species richness is not influenced by species abundance and therefore it is an appropriate measure for studying the distribution of the species. This type of analysis however, does not allow us to indentify which species in particular are impacted by the variables identified so I used generalized linear mixed modelling to study interactions between habitat variables and certain species specific behavioural, morphological, and life history characteristics (including food choice, body length and clutch size), to examine how abundances and presence/absence are influenced by those variables in each site. The results are of significant conservation importance as they give us valuable insight on: a) which factors are most important in determining species richness and b) what species characteristics make birds more vulnerable to change in these factors. Moreover, the results demonstrate that by using an appropriate statistical method there is potential to successfully utilize the enormous amount of available information to derive important conservation conclusions.

This research examines factors influencing avian reproductive biology in three co-occurring woodland passerines, Cyanistes caeruleus (blue tit), Parus major (great tit), and Ficedula hypoleuca (pied flycatcher), breeding in nestboxes at Nagshead Nature Reserve (Gloucestershire, U. K. ). The study uses breeding data on the study species collected by the Royal Society for the Protection of Birds (RSPB) between 1990 and 2004, together with site-based ringing records for F. hypoleuca and primary data from field and laboratory work undertaken during 2005 and 2006. Breeding productivity of C. caeruleus and P. major declined over the study period, despite breeding populations that were increasing (C. caeruleus) and stable (P. major). The breeding population of F. hypoleuca declined by 73% (much more severely than nationally). Decline was apparently driven by decreasing productivity and changes in the North Atlantic Oscillation cycle. Phenological changes in lay date were apparent for C. caeruleus (mean lay date advanced by five days in 15 years) and P. major (increased within-season variability in clutch initiation). No change was apparent for F. hypoleuca, possibly due to migration constraining phenological adjustment. The relationship between lay date and clutch size was found to be annually variable, rather than a constant as hitherto assumed. The strength of this relationship correlated with breeding density (C. caeruleus and P. major), the "earliness" of the breeding season (P. major), and mean May temperature (F. hypoleuca). The potential influence of nestbox orientation on nest-site selection and reproductive success was investigated. Orientation correlated with nestling survival for F. hypoleuca and offspring quality for P. major (both lowest in boxes oriented south-southwest). In the case of P. major, boxes facing south-southwest were avoided by adult birds, suggesting adaptive nest-site selection. Microbial load (specifically the abundance of the fungus Epicoccump urpurascens)was related to both orientation and P. major offspring quality, providing a possible explanation for observed patterns of nest-site selection behaviour. Ectoparasite load was not linked to nestbox orientation or P. major offspring quality. These findings provide insights into aspects of population biology (relationship between phenology and productivity), evolutionary ecology (adaptive nest-site choice to maximise offspring fitness) and the interactions between species and their abiotic and biotic environments (influence of orientation and microbial load on breeding success). Relevance of these results to conservation and in situ species management is discussed. Recommendations for optimal siting of nestboxes are given.