Urbanisation is one of the most pervasive forms of habitat change. More than half of the world’s human population now resides in urban areas, and urban land cover is projected to triple between 2000 and 2030 (1). This poses major threats to single species, biodiversity and ecosystem services (1). Nevertheless, some species may be able to establish in urban areas, where they usually display strong physiological and behavioural changes compared to their counterparts living in natural habitats (2). Ultimately, the future of these urban populations will depend on their ability to adapt to city life (3).
There is increasing recognition that urbanisation can profoundly modify not only the spatial environment, but also the temporal one (4). Particularly critical are artificial light at night and locally elevated sound levels, which can affect the natural rhythmic environment, disrupt organismal clocks, interfere with sensory perception, and ultimately lead to associated changes along the food chain (for example, behaviour of prey) (5). However, such evidence comes mostly from diurnal species, which have been found to expand their activity into the night to extend foraging time and increase mating success, exploiting the presence of light pollution to see and move through the urban night (6, 7). In contrast, there is a surprising lack of data from nocturnal species. Nocturnal species may also be strongly affected by light at night, especially in the case of prey that want to avoid being seen by predators. Moreover, nocturnal predators often hunt using acoustic cues, which makes them susceptible to anthropogenic noise, too (8). On one hand, these acoustic hunters may be forced to forage during quieter periods of the night, for instance by avoiding activity at noisy rush hours. On the other hand, they might switch between sensory cues and rely more on visual hunting in noisy areas, perhaps even exploiting areas polluted by anthropogenic light to find their prey. Distinguishing between these competing, although not fully exclusive hypotheses, will provide novel and exciting insights into how species may adapt to anthropogenic temporal environments.
This project will approach this unique challenge by studying Tawny owls (Strix aluco) (Fig. 1), a nocturnal predator that usually prey by sound. Individual owls will be tracked around-the-clock, using accelerometers to detail behaviour (Fig. 2), GPS to detail space use (Fig. 3), and soundmeters and lightmeters to detail the sensory environments experienced by the birds. Simultaneously, we will quantify the lightscapes and soundscapes in which these raptors move, by around-the-clock, on-animal recordings using dedicated sensors. We will further collect data from nests about provisioning rates, delivered food items, and breeding success. Specifically, this project has three fundamental objectives:
• Objective 1: Timing of activities in city- and forest-dwelling owls: To quantify the plasticity in timing of Tawny owls using accelerometry data.
• Objective 2: Moving through urban lightscapes and soundscapes: To examine how sensory pollutants (light and noise) shape foraging behaviour and foraging efficiency. To this end we will use on-bird measures of light and high-resolution GPS data, and from ground measurements of noise. Using these data, we will build movement models to identify spatio-temporal responses of owls to time-structured, anthropogenic changes to their habitats.
• Objective 3: Links to diet and reproductive success: To identify how the modified use of time and space in urban areas impacts on diet and reproductive success. Decreased parental foraging efficiency, delivery of fewer or lower quality food items, and disrupted rest phases could all impact nestlings’ body condition and fledging success.