Dusk

Abstract: It is well established that artificial night lighting can influence animal orientation, but there is less information about its effects on other behaviors. Previous work suggested that light pollution can affect both seasonal and daily patterns of behavior. The aim of our study was to investigate the effects of artificial night lighting and daytime traffic noise on the timing of dawn and dusk singing in 6 common songbirds. We recorded singing behavior in 11 nonurban plots: 2 plots with light, but no noise, 3 with light and noise pollution, 3 with noise, but no light, and 3 undisturbed forests. Our results show that artificial night lighting, but not noise, leads to an earlier start of dawn singing in 5 out of 6 species, ranging on average from 10 min for the song thrush to 20 min for the robin and the great tit. This effect was strongest at higher light intensities. W e further show that dusk song is also affected: 3 species continued dusk singing for longer in lighted areas, but the effect was smaller than that observed for dawn song (from about 8 min for the blackbird to 14 min for the great tit). For all species, onset and cessation of singing changed relative to sunrise and sunset with the progress of the s eason. Rain delayed the onset of singing at dawn and advanced the cessation at dusk. We discuss the implications of our findings in the context of sexual selection.

Abstract: Artificial night lighting is expanding globally, but its ecological consequences remain little understood. Animals often use changes in day length as a cue to time seasonal behaviour. Artificial night lighting may influence the perception of day length, and may thus affect both circadian and circannual rhythms. Over a 3.5 month period, from winter to breeding, we recorded daily singing activity of six common songbird species in 12 woodland sites, half of which were affected by street lighting. We previously reported on analyses suggesting that artificial night lighting affects the daily timing of singing in five species. The main aim of this study was to investigate whether the presence of artificial night lighting is also associated with the seasonal occurrence of dawn and dusk singing. We found that in four species dawn and dusk singing developed earlier in the year at sites exposed to light pollution. We also examined the effects of weather conditions and found that rain and low temperatures negatively affected the occurrence of dawn and dusk singing. Our results support the hypothesis that artificial night lighting alters natural seasonal rhythms, independently of other effects of urbanization. The fitness consequences of the observed changes in seasonal timing of behaviour remain unknown.

Abstract: Long-term tracking using global positioning systems (GPS) is widely used to study vertebrate movement ecology, including fine-scale habitat selection as well as large-scale migrations. These data have the potential to provide much more information about the behavior and ecology of wild vertebrates: here we explore the potential of using GPS datasets to assess timing of activity in a chronobiological context. We compared two different populations of deer (Cervus elaphus), one in the Netherlands (red deer), the other in Canada (elk). GPS tracking data were used to calculate the speed of the animals as a measure for activity to deduce unbiased daily activity rhythms over prolonged periods of time. Speed proved a valid measure for activity, this being validated by comparing GPS based activity data with head movements recorded by activity sensors, and the use of GPS locations was effective for generating long term chronobiological data. Deer showed crepuscular activity rhythms with activity peaks at sunrise (the Netherlands) or after sunrise (Canada) and at the end of civil twilight at dusk. The deer in Canada were mostly diurnal while the deer in the Netherlands were mostly nocturnal. On an annual scale, Canadian deer were more active during the summer months while deer in the Netherlands were more active during winter. We suggest that these differences were mainly driven by human disturbance (on a daily scale) and local weather (on an annual scale). In both populations, the crepuscular activity peaks in the morning and evening showed a stable timing relative to dawn and dusk twilight throughout the year, but marked periods of daily a-rhythmicity occurred in the individual records. We suggest that this might indicate that (changes in) light levels around twilight elicit a direct behavioral response while the contribution of an internal circadian timing mechanism might be weak or even absent.