A Multidimensional Framework for Assessing the Direct and Indirect Effects of Urbanization on Avian Breeding Fitness: Integrating Environmental Factors, Food Resources, and Citizen Science for Species Conservation in Urban Landscapes

Chen, Sihao (2025) A Multidimensional Framework for Assessing the Direct and Indirect Effects of Urbanization on Avian Breeding Fitness: Integrating Environmental Factors, Food Resources, and Citizen Science for Species Conservation in Urban Landscapes PhD thesis, University of Liverpool.

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Abstract

Urbanization is one of the defining issues of the Anthropocene, leading to dramatic transformation of land-cover patterns all around the Earth. This transformation has detrimental effects on global biodiversity and threatens the carrying capacity of our ecosystems. Three key environmental issues are associated with urbanization. First, urbanization affects ecosystem functioning and, particularly where it becomes more intense, it often results in reduced species richness and abundance. Second, the urban heat-island effect (UHI) and sensory pollutants such as noise pollution and artificial light at night (ALAN) cause detrimental effects on wildlife by advancing breeding dates, impairing communication and reducing breeding fitness. Third, urbanization can also imply a reduction in available food resources that is commonly perceived as the main constraint to breeding fitness for urban organisms — usually referred to as the food limitation hypothesis. The overall aims of this study were therefore to investigate how these different factors directly and indirectly interact, and their relative importance in shaping the fitness of wild organisms. The Barn Swallow Hirundo rustica is a perfect model species to study these questions. This human commensal is one of the few species that has coexisted with humans for thousands of years, and in China it is regarded as a symbol of good luck. It is also an aerial insectivore that benefits farmlands and croplands and controls urban pest populations, and its diet overlaps with many other insectivores, making the results applicable to a wide range of urban species. Moreover, Barn Swallow populations and other aerial insectivores are experiencing steep declines all around the world. Investigating the current status of Barn Swallow rural and urban populations, its interactions with humans, and deepening our understanding on the consequences of increased urbanization, are thus top research priorities. Here, I first developed a multidimensional framework to act as a theoretical foundation for understanding how different facets of the urban ecosystem interact to affect bird breeding fitness. In my first field project, I collected Barn Swallow breeding data regarding laying dates, clutch size, number of hatchling and fledgling, hatching and fledging success, and insect biomass at the colony level, quantifying environmental variables and dietary composition for active nests (N=53) at the nest and colony level. The results showed that urbanization and laying behavior were directly related to insect abundance, phenological mismatch and diet of Barn Swallows while UHI was indirectly related to phenological mismatch and diet. Finally, direct negative effects of insect diets (e.g., flies) on fledging success of Barn Swallows, and indirect positive effects on fledging success of later laying date were recorded. In the second field project, I used Barn Swallow nesting locations from a nationwide citizen science as well as associated environmental variables at the site and landscape levels. This study revealed that UHI effects at the site scale, and ALAN and road simplicity at the landscape scale were positively associated with Barn Swallow nest abundance while building year had a negative impact on Barn Swallow nests. Overall, results suggest Barn Swallow can respond to these mixed effects at multiple spatial scales and efficiently adapt to various environmental conditions across the urbanized landscape. The studies presented in this thesis demonstrated that adopting a multidimensional framework in urban ecology can lead to a comprehensive understanding of both direct and indirect, as well as positive and negative effects of urbanization and environmental factors on species’ habitat selection and breeding parameters. Utilizing a multidimensional framework also enables us to plan and design urban environments in order to minimize the adverse impacts of urbanization for both biodiversity and people.

Item Type:	Thesis (PhD)
Uncontrolled Keywords:	urbanization, environmental filter, urban heat island (UHI), noise pollution, artificial light at night (ALAN), food resources, diet, trophic interaction, life-history traits, breeding fitness, Phenological mismatch, urban planning, land use zoning, road, building, Barn Swallow Hirundo rustica
Divisions:	Faculty of Science & Engineering Faculty of Science & Engineering > School of Environmental Sciences
Depositing User:	Symplectic Admin
Date Deposited:	18 Aug 2025 09:10
Last Modified:	18 Aug 2025 09:10
DOI:	10.17638/03192656
Supervisors:	Goodale, Eben Patrick, Samantha Nunez, Emilio Pagan
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3192656
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