The consequences of urbanisation and artificial light at night on wildlife health and physiology: insights from avian systems

Reid, Rachel Rose (2025) The consequences of urbanisation and artificial light at night on wildlife health and physiology: insights from avian systems. PhD thesis, University of Glasgow.

Abstract

Urbanisation is accelerating at an unprecedented rate globally, exposing urban wildlife to a suite of novel anthropogenic stressors that can significantly impact health and fitness. One of the most pervasive of these stressors is Artificial light at night (ALAN) which can impact species at multiple levels of the ecosystem through the disruption of natural light-dark cycles that are essential for the regulation of many biological and ecological processes. Despite growing awareness of these threats, our understanding of how urbanisation and specific urban stressors like ALAN affect wildlife health remains limited, as does our knowledge of the mechanisms driving these relationships. A deeper understanding is vital for developing effective mitigation strategies that balance human needs with the conservation of vulnerable species in the face of urban expansion. As urbanisation continues to intensify, assessing its effects on wildlife health and fitness becomes increasingly urgent. This requires the use of reliable health biomarkers to generate consistent and biologically meaningful evidence in ecological studies. This thesis integrates experimental, and meta-analytical approaches to provide a comprehensive assessment of how urbanisation influences physiology and health in avian study systems. It also addresses the methodological challenges of measuring health in ecological contexts, with a focus on high intraindividual variation in physiological biomarkers, which can obscure meaningful patterns.

To address these knowledge gaps, I first conducted a phylogenetically controlled global meta-analysis to evaluate the relationship between urbanisation and avian health, identifying the biological and methodological factors that influence this relationship. While some studies suggest urbanisation negatively impacts avian health, findings have been inconsistent, and this is likely due to variability in study locations, focal species, and biomarker types. By collating data across a variety of studies, I was able to identify key drivers of variation and reveal hidden patterns. Notably, urbanisation was found to negatively impact avian health only when it was measured as a continuous variable (urban score), rather than as a binary categorical variable (urban vs non-urban classification). This finding emphasises the importance of quantifying urbanisation in a way that captures its heterogeneity for the detection of subtle relationships. The results also highlight that the impacts of urbanisation on avian health are context dependent, influenced by factors such as life stage and biomarker type.

I then narrowed the focus to investigate the effects of ALAN exposure on multiple health biomarkers in birds, using both field and captive study designs. In the field, I exposed great tit (Parus major) nestlings to ALAN from hatching to fledging using artificial nest boxes, targeting the sensitive developmental period where exposure to stressors is likely to have stronger consequences. Additionally, in a captive experiment, I exposed adult zebra finches (Taeniopygia guttata) to ALAN over four months to assess its long-term physiological effects using a longitudinal design. To explore potential mitigation strategies, I also tested a partial light at night treatment in the captive experiment in which lights were turned off for half of the night, comparing its effects to those of the full night ALAN exposure.

In both experiments, I adopted a multi-biomarker approach to capture different dimensions of health, addressing its multivariate nature. In the field, ALAN exposure did not show any consistent negative effect on oxidative stress or corticosterone levels in nestlings, but it was shown to significantly reduce body condition. In the captive study, ALAN increased telomere loss and disrupted glucose circadian rhythms, although it had no detectable effects on the oxidative stress markers assessed. Importantly, these negative effects were absent in the partial light at night treatment group, suggesting that this mitigation strategy may provide a viable means of reducing the impact of ALAN on wildlife health. These findings highlight the complex and variable nature of the effects of ALAN on health and show the potential for mitigation through the use of altered light exposure regimes.

I then explored the methodological challenges involved in measuring health by focusing on oxidative stress biomarkers, which are commonly used to assess fitness and physiological condition, particularly in research focusing on ageing and ageing related diseases. Through a comprehensive meta-analysis, I demonstrated that oxidative stress markers exhibit generally low within-individual repeatability, regardless of taxa, sex, environment, biomarker type, or study design. Using a simulation study, I further showed that this low repeatability can obscure associations with other traits, including telomere length. While increasing samples sizes and the number of repeated measures per individual can help mitigate this issue, further work is needed to develop robust approaches that address these detection limitations. These findings highlight the importance of careful experimental design and cautious interpretation when using highly variable physiological biomarkers in ecological studies.

The findings of this thesis contribute to the growing body of literature looking into the effects of urbanisation and anthropogenic stressors on wildlife health and well-being. By examining these issues and considering species traits, life stages, environmental factors, and employing a multi-biomarker approach, this work advances our understanding how urban environments shape wildlife health. Furthermore, insights into the use and limitations of oxidative stress markers will inform future studies and support the development of reliable assessment of health and physiology in wild populations. This research enhances our understanding of the complex interactions between urbanisation, anthropogenic stressors, and wildlife health, providing a foundation for developing evidence-based mitigation strategies to reduce the negative effects of urban stressors such as ALAN. This research also lays the groundwork for future research on key areas, including the mechanistic pathways underlying these relationships, the cumulative long-term effects of urbanisation, and the development of realistic, scalable interventions to reduce negative impacts of urbanisation on biodiversity.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Supported by funding from the Wild Animal Initiative.
• Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences; Q Science > QP Physiology
• Colleges/Schools: College of Medical Veterinary and Life Sciences > Institute of Biodiversity Animal Health and Comparative Medicine
• Funder's Name: Wild Animal Initiative
• Supervisor's Name: Dominoni, Dr. Davide and Boonekamp, Dr. Jelle
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85347
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 15 Jul 2025 10:48
• Last Modified: 15 Jul 2025 10:48
• URI: https://theses.gla.ac.uk/id/eprint/85347

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