Understanding the dual impacts of urbanisation and climate change on breeding in one of the UK's most common city birds, the Blue Tit (Cyanistes caeruleus).

Pattison-Willits, Victoria Sarah (2023). Understanding the dual impacts of urbanisation and climate change on breeding in one of the UK's most common city birds, the Blue Tit (Cyanistes caeruleus). University of Birmingham. Ph.D.

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Human activities cause widespread and irreversible modifications to once natural and semi-natural environments, creating novel conditions and challenges for wildlife. In particular, the ongoing combined effects of increasing urbanisation and global climate change are likely to result in some of the most extreme and significant changes to once natural landscapes, with profound impacts across multiple ecological levels, including individual organisms and populations. Yet despite increasing evidence to suggest that climate change is already exacerbating the effects of urbanisation, few studies have considered how species may respond to the combined impacts of these two factors. In particular, considering that reproductive success is crucial to the long-term stability of populations and the survival of species, there is a clear need to better understand how breeding phenology and success are affected by increasing urbanisation, and variation in weather conditions in these already heavily impacted systems.

This thesis focuses on a population of Blue Tits, a small hole-nesting passerine, that is widely considered to be an urban-adapted species and is commonly used in urban-rural comparative research. Using a quantitative and hierarchical mixed modelling approach I investigated how breeding success during two reproductive phases (pre-hatching and brood-rearing) varied across a short, high resolution intra-city urban gradient in the city of Birmingham, UK using demographic data from consecutive years (2013-2018). The aims of the work were to: 1) identify the key habitat and landscape-scale factors that impact breeding outcomes, 2) determine if the strength and direction of these effects vary across the different phases of breeding, 3) use critical climate time window analyses to explore the influence of variation in both temperature and rainfall across the urban gradient on a selection of breeding responses identified as key drivers in determining breeding success in this population.

I found evidence for a subtle yet quantifiable negative effect of increasing urbanisation across both breeding stages. However, the brood-rearing phase appeared particularly sensitive to variation in urbanisation, with the mean body mass of nestlings, individual fledging probability and rates of fledging success all declining with increasing built landcover. Crucially brood reduction during the early phase of nestling development, and an increased risk of complete breeding failure during brood-rearing appeared to be the main drivers of observed reduced breeding success across a city scale urban gradient. At the site level, variation in the composition and structure of vegetation within greenspaces, in particular the number of native broadleaved trees and the diversity of tree species was also found to significantly influence breeding outcomes. Aligned with these findings, the early brood rearing stage was also determined to potentially be the most sensitive to changes in the prevailing weather conditions. The urban environment appeared to buffer the effects of cold temperatures, whilst increased maximum temperatures were associated with heavier nestlings and higher rates of fledging success. However, model predictions suggested a critical threshold at which point higher maximum temperatures were linked to lower fledging success. Higher rainfall during this period was also associated with lighter nestling body mass and reduced fledging success. Furthermore, there was tentative evidence to suggest that the detrimental effects of adverse weather may be compounded by the urban gradient. My study demonstrates that the impacts of both urbanisation and weather variation are complex and unlikely to be consistent across the breeding season. However, findings did suggest that environmental conditions during the critical brood-rearing phase are likely crucial to nestling growth, development and survival to fledging. As condition of chicks when they leave the nest determines their long-term survival and future reproductive success these findings have wider implications for the future of this and other populations of urban breeding birds, already undergoing increasing environmental stress from the multiple threats of further rapid urbanisation and the increasing intensity and duration of extreme weather associated with climate change.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Licence: All rights reserved
College/Faculty: Colleges (2008 onwards) > College of Life & Environmental Sciences
School or Department: School of Geography, Earth and Environmental Sciences
Funders: None/not applicable
Subjects: Q Science > QH Natural history
Q Science > QH Natural history > QH301 Biology
Q Science > QL Zoology
URI: http://etheses.bham.ac.uk/id/eprint/13673


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