Abstract: To keep pace with progressing urbanization organisms must cope with extensive habitat change. Anthropogenic light and noise have modified differences between day and night, and may thereby interfere with circadian clocks. Urbanized species, such as birds, are known to advance their activity to early morning and night hours. We hypothesized that such modified activity patterns are reflected by properties of the endogenous circadian clock. Using automatic radio-telemetry, we tested this idea by comparing activity patterns of free-living forest and city European blackbirds (Turdus merula). We then recaptured the same individuals and recorded their activity under constant conditions. City birds started their activity earlier and had faster but less robust circadian oscillation of locomotor activity than forest conspecifics. Circadian period length predicted start of activity in the field, and this relationship was mainly explained by fast-paced and early-rising city birds. Although based on only two populations, our findings point to links between city life, chronotype and circadian phenotype in songbirds, and potentially in other organisms that colonize urban habitats, and highlight that urban environments can significantly modify biologically important rhythms in wild organisms.

Abstract: With urban areas growing worldwide, so does artificial light at night (ALAN) which negatively affects many nocturnal animals, including bats. The response of bats to ALAN ranges from some opportunistic species taking advantage of insect aggregations around street lamps, particularly those emitting ultraviolet (UV) light, to others avoiding lit areas at all. Tree cover has been suggested to mitigate the negative effects of ALAN on bats by shielding areas against light scatter. Here, we investigated the effect of tree cover on the relationship between ALAN and bats in Berlin, Germany. In particular, we asked if this interaction varies with the UV light spectrum of street lamps and also across urban bat species. We expected trees next to street lamps to block ALAN, making the adjacent habitat more suitable for all species, irrespective of the wavelength spectrum of the light source. Additionally, we expected UV emitting lights next to trees to attract insects and thus, opportunistic bats. In summer 2017, we recorded bat activity at 22 green open spaces in Berlin using automated ultrasonic detectors. We analyzed bat activity patterns and landscape variables (number of street lamps with and without UV light emission, an estimate of light pollution, and tree cover density around each recording site within different spatial scales) using generalized linear mixed-effects models with a negative binomial distribution. We found a species-specific response of bats to street lamps with and without UV light, providing a more detailed picture of ALAN impacts than simply total light radiance. Moreover, we found that dense tree cover dampened the negative effect of street lamps without UV for open-space foraging bats of the genera Nyctalus, Eptesicus, and Vespertilio, yet it amplified the already existing negative or positive effect of street lamps with or without UV on Pipistrellus pipistrellus, P. pygmaeus, and Myotis spp. Our study underpins the importance of minimizing artificial light at night close to vegetation, particularly for bats adapted to spatial complexity in the environment (i.e., clutter-adapted species), and to increase dense vegetation in urban landscape to provide, besides roosting opportunities, protection against ALAN for open-space foraging bats in city landscapes.