Are cities ecological traps? High-throughput DNA sequencing reveals seasonal changes in the diet and fitness of a common songbird

Dr Davide Dominoni, University of Glasgow
RSE Small Research Grant awardee

Dr Davide Dominoni. Photo: Ian Georgeson Photography

Urban landscapes are one of the fastest-growing ecosystems on Earth. As natural land is converted to built-up infrastructure, changes in food availability, temperature, sound, light, and pollution levels create a novel environment with health implications for the residing animal populations.

Changes in behaviour and physiology are especially evident in birds; however, the impact of urban environments on health, fitness, and diversity is not well understood. The concern is that urban centres are becoming ‘ecological traps’ for breeding songbirds who are attracted by factors such as warmer temperatures and supplementary food resources provided by humans. For researchers, it is crucial to understand what factors influence species’ success or failure in these ubiquitous environments to maintain biodiversity in our rapidly urbanising world.

Dr Davide Dominoni (L) with Research Technician Dr Paul Baker (R). Photo: Ian Georgeson Photography

Dr Davide Dominoni was awarded an RSE Small Research Grant to expand on his previous research initiated in 2014, which investigated the impact of the urban environment on Blue Tits. Like many common songbirds, Blue Tits are abundant in cities, however, Dr Dominoni’s research has shown that their reproduction suffers in urban habitats, where they lay smaller clutches and the health of the offspring is often impaired.

Using advances in DNA analysis, Dr Davide Dominoni and his team at the University of Glasgow worked with colleagues Dr Andreanna Welch and Miss Rachel McConnell at Durham University to sequence adult and offspring Blue Tit faeces to identify their diet during winter and how this impacted their subsequent breeding success.

Blue Tit chicks. Photo: Ian Georgeson Photography

The researchers were looking to see whether human population, light pollution, food availability, and/or temperature drove differences in diet and on the number of chicks that fledged as a result. By quantifying these environmental characteristics around a 50m radius from each nestbox, the team found that the availability of oak and birch trees impacted the number of chicks that fledged, and where more of these trees were present, more chicks successfully fledged. This is due to native trees, such as oak and birch, supporting healthy caterpillar populations; an optimal food source for Blue Tits, crucial to the development of healthy chicks.

Speaking about the RSE-supported project, Dr Dominoni said, “The RSE award enabled us to extend our work over winter. We monitored the Blue Tits at two urban parklands in Glasgow city centre and two oak woodlands located near the Scottish Centre for Ecology and the Natural Environment (SCENE) on the edge of Loch Lomond. We found that while the adult Blue Tit diet was not affected by urbanisation in winter or spring, the offspring in more urbanised areas were fed with considerably fewer caterpillars, which led to slower growth and poorer health. This finding is crucial because it supports the idea of cities likely being ecological traps.”

Dr Dominoni notes that Blue Tit populations are likely to withstand urban environmental pressures, as their abundance sees regular immigration from rural areas. However, for other, less copious species, urban centres might not be an option, which is why biodiversity is usually negatively affected by urbanisation.

“Identifying how urban diet relates to the reproductive outcomes of Blue Tits in Scotland could enable more informed management plans to be developed in cities nationally and further afield. Our research suggests that urban planting regimes should be carefully considered, selecting tree species that are native, or allied to native species, that can support native insect populations. This will not only help to support complete food chains, but also to maximise biodiversity and ecosystem services of urban green spaces.”

Dr Davide Dominoni

Dr Davide Dominoni checks a nesting box. Photo Ian Georgeson Photography

The next step of Dr Dominoni’s work is to develop population models that will test the hypothesis of cities acting as ecological traps by considering all demographic variables—reproduction, survival, and immigration—together. Dr Dominoni and his team believe in the value of long-term ecological monitoring to understand the impact of human activities on wildlife health and biodiversity. They have collected over ten years’ worth of data from the Glasgow Urban Gradient, providing an extensive dataset that can be used to ask questions on urban ecology that would not been otherwise possible to answer.



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