No abstract

Artificial light at night (LAN) has become a stressor of global extent. Previous work has highlighted the high potential of LAN to interfere with annual and diel rhythms of seasonal organisms as well as to affect interactions at the community level. However, our understanding how LAN induced alterations of activity and breeding cycles affect the reproductive outcome and fitness of the birds is still limited. Here, we focus on the effects of night time illumination on the breeding biology of urban European blackbirds Turdus merula. Our results indicate that blackbirds prefer illuminated nest sites and advance their date of clutch initiation by 6 d per 1 lux of night time illumination. Furthermore, daily nest survival rates increased with increasing LAN although this effect was most pronounced for the transition from dark to slightly illuminated sites. We suggest that blackbirds breeding under low artificial night light conditions benefit from the LAN-avoidance of their major predators (nocturnal) whereas predominant predators of blackbirds nesting in the city centre are diurnal and are, thus, not affected by LAN. Hence, it seems likely that both direct effects of LAN on the timing of reproduction as well as indirect effects on interspecific interactions might contribute to the observed changes in the breeding biology of European blackbirds. This study emphasizes the diverse ecological effects of the night time illumination which are -in its complexity -still poorly understood.

In order to maximize their fitness, organisms in seasonal environments rely on external cues to optimally time their life‐history stages. One of the most important zeitgeber to time reproduction is the photoperiod, but further environmental cues are assessed to fine‐tune reproduction due to year‐to‐year variation in environmental conditions. However, in urbanized environments, the pervasive artificial light at night has altered the natural signal of light and darkness. Accordingly, artificial light at night was repeatedly shown to affect avian reproductive physiology and to advance seasonal reproduction in birds. However, these experiments were mainly conducted in the absence of further environmental cues to facilitate the investigation of the mechanisms which are still poorly understood. Here, we investigate whether the endocrine system of free‐ranging European blackbirds (Turdus merula) correlates with the amount of artificial light at night along a rural to urban gradient while the birds still encounter complementary environmental cues including seasonal variation in day length and temperature. Testosterone and estrone were assessed as metabolites in fecal samples and corticosterone in blood from mist‐netted blackbirds. We demonstrate that seasonal fluctuations in abiotic factors, individual conditions, but also light at night affect the reproductive and stress physiology of wild European blackbirds. Elevated artificial night light intensities were significantly positively correlated with corticosterone and negatively with female estrone levels. No effects of artificial light were found for testosterone levels. Our results suggest that female blackbirds in particular perceive even low levels of artificial light at night as a weak but chronic stressor that interacts with the hypothalamic‐pituitary‐gonadal axis and leads to a reduced secretion of reproductive hormones. These findings point out that the impacts of light pollution are diverse and we only slowly disentangle its multiple effects on physiology, ecology, and biodiversity.

Monitoring studies at the landscape level are complex, expensive and difficult to conduct. Many aspects have to be considered to avoid confounding effects which is probably the reason why they are not regularly performed in the context of risk assessments of plant protection products to pollinating insects. However, if conducted appropriately their contribution is most valuable. In this paper we identify the requirements of a large-scale monitoring study for the assessment of side-effects of clothianidin seed-treated winter oilseed rape on three species of pollinating insects (Apis mellifera, Bombus terrestris and Osmia bicornis) and present how these requirements were implemented. Two circular study sites were delineated next to each other in northeast Germany and comprised almost 65 km2 each. At the reference site, study fields were drilled with clothianidin-free OSR seeds while at the test site the oilseed rape seeds contained a coating with 10 g clothianidin and 2 g beta-cyfluthrin per kg seeds (Elado®). The comparison of environmental conditions at the study sites indicated that they are as similar as possible in terms of climate, soil, land use, history and current practice of agriculture as well as in availability of oilseed rape and non-crop bee forage. Accordingly, local environmental conditions were considered not to have had any confounding effect on the results of the monitoring of the bee species. Furthermore, the study area was found to be representative for other oilseed rape cultivation regions in Europe.