Understanding the occurrence of animals in cities

Early urban ecology studies have compared places outside the city with places in the city to identify what species can life in the city. These studies have found that in the city centre, where most of the surface is sealed, very few animal species can live (such as the Marienplatz in Munich), while in other places within the city, many species occur. A study carried out during the PhD-thesis of Fabio Sweet in our group found that across 30 cities in Germany, 80% of species found in a radius of 50km outside the city are also found within one of the cities¹. However, many of these species only occur in a few places in the urban environment. In our research we aim to understand why a species occurs in one place of the city, but not in another. Understanding the conditions that allow species to live in the urban environment will help to design the city in a way that the species can live there. 

We investigated biodiversity in 100 urban squares, to understand how human design affects the occurrence of animals in cities. We focus on public squares (open spaces in a city without housing that are publicly accessible) as a core element of cities that serve as important public spaces where city dwellers have gathered since ancient times. The 103 squares are a representative sample of all squares in Munich and span gradients in size, distance to the city centre, and greenness on and in the surrounding of the squares. We monitored the abundance and diversity of various animal groups to investigate the effects of square properties on urban biodiversity. We found positive effects of an increasing greenness (proportion of grassy surface area, number of trees, shrub volume) on the abundance and diversity of various taxa². Importantly, we found that the most important variables also differed for different guilds within the same taxon, e.g. tree density on squares increased the abundance of tree- and ground-foraging birds, but had little effect on understorey-foraging birds³. Such birds benefit from the presence of shrubs. The greenness in a circle of 1km radius around the focal square increased pollinator abundance and small mammal activity, emphasising that several spatial scales can be important for biodiversity in an urban site. We are currently extending this study in the framework of Research Training Group in Urban Green Infrastructure, extending our study to more than 500 points in the city and studying not only birds, but also insects. 

We also combine bird recordings with measurements of tree structure in the project CitySoundscape, aiming to further increase how urban structure affects the occurrence of species. 

Another important limitation for animals in the city is ecological connectivity. In two PhD-theses we investigate how connectivity for animals can be measured and modelled in the city, and how such connectivity modelling can be included into urban planning. In the Ph.D.-thesis of Lisa Merkens, a new model for animal connectivity is developed and applied that uses new ways to integrate different types of species data for model parametrization. In the Ph.D.-thesis of Meret Pundsack, practical ways in which the ecological connectivity model can be integrated with models of other urban disciplines, such as traffic or microclimate planning, are sought, using multidisciplinary scenario creation and modelling (see CoCoNet-project).

Finally, we investigate human-animal interactions in “The Happy Pigeon Project”. Animals experience stressful lives needing to procure sufficient resources to survive and reproduce, while navigating predation threats and competition in the landscape. However, urbanisation introduces plenty of novel feeding opportunities for wildlife capable of exploiting them. Examples range from recreational bird feeding to food waste and litter. What happens then, when the pressure from food scarcity is relieved? Using urban feral pigeons as model organisms, the Happy Pigeon Project examines how food availability affects chronic stress in birds, using physiology (hormonal and morphological) and behaviour as wellbeing indicators. We conduct fieldwork in three German cities non-lethally managing pigeon populations via the Augsburg model, in which pigeons are provided food and nest sites (and their eggs destroyed to control breeding), thereby functioning as semi-natural food supplementary experiments. We also study captive feral populations, to understand how pigeons experience security - of resources, and from predators - when this comes at a cost of physical freedom. 

 Making cities more biodiversity-friendly also requires to activate architecture for the support of biodiversity. This is because constructions cover large parts of the urban footprint and designing these is the domain of architecture. In the project ECOLOPES, an EU-funded FET-Open project (2021-2025) we investigated how architecture, computational design and ecology can be integrated to create ecologically sound buildings⁵. ECOLOPES proposes a radical change for city development: instead of minimizing the negative impact of urbanisation on nature, we aim at urbanisation to be planned and designed such that nature –including humans– can co-evolve within the city. We envisage a radically new integrated ecosystem approach to architecture that focuses equally on humans, plants, animals, and associated organisms such as microbiota. ECOLOPES has provided core approaches, models and technology that will help to achieve this vision. More information can be found on the ECOLOPES homepage.